/met'euh fiz"iks/, n. (used with a sing. v.)
1. the branch of philosophy that treats of first principles, includes ontology and cosmology, and is intimately connected with epistemology.
2. philosophy, esp. in its more abstruse branches.
3. the underlying theoretical principles of a subject or field of inquiry.
4. (cap., italics) a treatise (4th century B.C.) by Aristotle, dealing with first principles, the relation of universals to particulars, and the teleological doctrine of causation.
[1560-70; < ML metaphysica < MGk () metaphysiká (neut. pl.), Gk tà metà tà physiká the (works) after the Physics; with reference to the arrangement of Aristotle's writings]

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Branch of philosophy that studies the ultimate structure and constitution of reality

e., of that which is real, insofar as it is real. The term, which means literally "what comes after physics," was used to refer to the treatise by Aristotle on what he himself called "first philosophy." In the history of Western philosophy, metaphysics has been understood in various ways: as an inquiry into what basic categories of things there are (e.g., the mental and the physical); as the study of reality, as opposed to appearance; as the study of the world as a whole; and as a theory of first principles. Some basic problems in the history of metaphysics are the problem of universals
i.e., the problem of the nature of universals and their relation to so-called particulars; the existence of God; the mind-body problem; and the problem of the nature of material, or external, objects. Major types of metaphysical theory include Platonism, Aristotelianism, Thomism, Cartesianism (See also dualism), idealism, realism, and materialism.

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      the philosophical study whose object is to determine the real nature of things—to determine the meaning, structure, and principles of whatever is insofar as it is. Although this study is popularly conceived as referring to anything excessively subtle and highly theoretical and although it has been subjected to many criticisms, it is presented by metaphysicians as the most fundamental and most comprehensive of inquiries, inasmuch as it is concerned with reality as a whole.

Nature and scope of metaphysics

Origin of the term
 Etymologically the term metaphysics is unenlightening. It means “what comes after physics”; it was the phrase used by early students of Aristotle to refer to the contents of Aristotle's treatise on what he himself called “first philosophy,” and was used as the title of this treatise by Andronicus of Rhodes, one of the first of Aristotle's editors. Aristotle had distinguished two tasks for the philosopher: first, to investigate the nature and properties of what exists in the natural, or sensible, world, and second, to explore the characteristics of “Being as such” and to inquire into the character of “the substance that is free from movement,” or the most real of all things, the intelligible reality on which everything in the world of nature was thought to be causally dependent. The first constituted “second philosophy” and was carried out primarily in the Aristotelian treatise now known as the Physica; the second, which Aristotle had also referred to as “theology” (because God was the unmoved mover in his system), is roughly the subject matter of his Metaphysica. Modern readers of Aristotle are inclined to take both the Physica and the Metaphysica as philosophical treatises; the distinction their titles suggest between an empirical and a conceptual inquiry has little foundation. Aristotle was not indifferent to factual material either in natural or in metaphysical philosophy, but equally he was not concerned in either case to frame theories for empirical testing. It seems clear, nevertheless, that if the two works had to be distinguished, the Physica would have to be described as the more empirical, just because it deals with things that are objects of the senses, what Aristotle himself called “sensible substance”; the subject matter of the Metaphysica, “that which is eternal, free of movement, and separately existent,” is on any account more remote. It is also evident that the connection marked in the original titles is a genuine one: the inquiries about nature carried out in the Physica lead on naturally to the more fundamental inquiries about Being as such that are taken up in the Metaphysica and indeed go along with the latter to make up a single philosophical discipline.

 The background to Aristotle's divisions is to be found in the thought of Plato, with whom Aristotle had many disagreements but whose basic ideas provided a framework within which much of his own thinking was conducted. Plato, following the early Greek philosopher Parmenides, who is known as the father of metaphysics, had sought to distinguish opinion, or belief, from knowledge and to assign distinct objects to each. Opinion, for Plato, was a form of apprehension that was shifting and unclear, similar to seeing things in a dream or only through their shadows; its objects were correspondingly unstable. Knowledge, by contrast, was wholly lucid; it carried its own guarantee against error, and the objects with which it was concerned were eternally what they were, and so were exempt from change and the deceptive power to appear to be what they were not. Plato called the objects of opinion phenomena (phenomenon), or appearances; he referred to the objects of knowledge as noumena (noumenon) (objects of the intelligence) or quite simply as realities. Much of the burden of his philosophical message was to call men's attentions to these contrasts and to impress them with the necessity to turn away from concern with mere phenomena to the investigation of true reality. The education of the Platonic philosopher consisted precisely in effecting this transition: he was taught to recognize the contradictions involved in appearances and to fix his gaze on the realities that lay behind them, the realities that Plato himself called Forms, or Ideas. Philosophy for Plato was thus a call to recognize the existence and overwhelming importance of a set of higher realities that ordinary men—even those, like the Sophists of the time, who professed to be enlightened—entirely ignored. That there were such realities, or at least that there was a serious case for thinking that there were, was a fundamental tenet in the discipline that later became known as metaphysics. Conversely, much of the subsequent controversy about the very possibility of metaphysics has turned on the acceptability of this tenet and on whether, if it is rejected, some alternative foundation can be discovered on which the metaphysician can stand.

Characterizations of metaphysics
      Before considering any such question, however, it is necessary to examine, without particular historical references, some ways in which actual metaphysicians have attempted to characterize their enterprise, noticing in each case the problems they have in drawing a clear line between their aims and those of the practitioners of the exact and empirical sciences. Four views will be briefly considered; they present metaphysics as: (1) an inquiry into what exists, or what really exists; (2) the science of reality, as opposed to appearance; (3) the study of the world as a whole; (4) a theory of first principles. Reflection on what is said under the different heads will quickly establish that they are not sharply separate from one another, and, indeed, individual metaphysical writers sometimes invoke more than one of these phrases when asked to say what metaphysics is—as, for example, the British Idealist F.H. Bradley does in the opening pages of his work Appearance and Reality (1893).

An inquiry into what exists
      A common set of claims on behalf of metaphysics is that it is an inquiry into what exists; its business is to subject common opinion on this matter to critical scrutiny and in so doing to determine what is truly real.

      It can be asserted with some confidence that common opinion is certainly an unreliable guide about what exists, if indeed it can be induced to pronounce on this matter at all. Are dream objects real, in the way in which palpable realities such as chairs and trees are? Are numbers real, or should they be described as no more than abstractions? Is the height of a man a reality in the same sense in which he is a reality, or is it just an aspect of something more concrete, a mere quality that has derivative rather than substantial being and could not exist except as attributed to something else? It is easy enough to confuse the common man with questions like these and to show that any answers he gives to them tend to be ill thought-out. It is equally difficult, however, for the metaphysician to come up with more satisfactory answers of his own. Many metaphysicians have relied, in this connection, on the internally related notions of substance, quality, and relation; they have argued that only what is substantial truly exists, although every substance has qualities and stands in relation to other substances. Thus, this tree is tall and deciduous and is precisely 50 yards north of that fence. Difficulties begin, however, as soon as examples like these are taken seriously. Assume for the moment that an individual tree—what might be called a concrete existent—qualifies for the title of substance; it is just the sort of thing that has qualities and stands in relations. Unless there were substances in this sense, no qualities could be real: the tallness of the tree would not exist unless the tree existed. The question can now be raised what the tree would be if it were deprived of all its qualities and stood in no relations. The notion of a substance in this type of metaphysics is that of a thing that exists by itself, apart from any attributes it may happen to possess; the difficulty with this notion is to know how to apply it. Any concrete thing one selects to exemplify the notion of substance turns out in practice to answer a certain description; this means in effect that it cannot be spoken of apart from its attributes. It thus emerges that substances are no more primary beings than are qualities and relations; without the former one could not have the latter, but equally without the latter one could not have the former.

 There are other difficulties about substance that cannot be explored here—e.g., whether a fence is a substance or simply wood and metal shaped in a certain way. Enough has already been said, however, to indicate the problems involved in defining the tasks of metaphysics along these lines. There is, nevertheless, an alternative way of understanding the notion of substance: not as that which is the ultimate subject of predicates but as what persists through change. The question “What is ultimately real?” is, thus, a question about the ultimate stuff of which the universe is made up. Although this second conception of substance is both clearer and more readily applicable than its predecessor, the difficulty about it from the metaphysician's point of view is that it sets him in direct rivalry with the scientist. When the early Greek philosopher Thales (Thales of Miletus) inquired as to what is ultimately real and came up with the surprising news that all is water, he might be taken as advancing a scientific rather than a philosophical hypothesis. Although it is true that later writers, such as Gottfried Wilhelm Leibniz (Leibniz, Gottfried Wilhelm), a German Rationalist philosopher and mathematician, were fully aware of the force of scientific claims in this area and, nevertheless, rejected them as metaphysically unacceptable, the fact remains that the nonphilosopher finds it difficult to understand the basis on which a Leibniz rests his case. When Leibniz said that it is monads (monad) (i.e., elementary, unextended, indivisible, spiritual substances that enter into composites) that are the true atoms of nature and not, for example, material particles, the objection can be raised as to what right he has to advance this opinion. Has he done any scientific work to justify him in setting scientific results aside with such confidence? And if he has not, why should he be taken seriously at all?

The science of ultimate reality
      To answer these questions, another description of metaphysics has been proposed: that it is the science that seeks to define what is ultimately real as opposed to what is merely apparent.

      The contrast between appearance and reality, however, is by no means peculiar to metaphysics. In everyday life people distinguish between the real size of the Sun and its apparent size, or again between the real colour of an object (when seen in standard conditions) and its apparent colour (nonstandard conditions). A cloud appears to consist of some white, fleecy substance, although in reality it is a concentration of drops of water. In general, men are often (though not invariably) inclined to allow that the scientist knows the real constitution of things as opposed to the surface aspects with which ordinary men are familiar. It will not suffice to define metaphysics as knowledge of reality as opposed to appearance; scientists, too, claim to know reality as opposed to appearance, and there is a general tendency to concede their claim.

      It seems that there are at least three components in the metaphysical conception of reality. One characteristic, which has already been illustrated by Plato, is that reality is genuine as opposed to deceptive. The ultimate realities that the metaphysician seeks to know are precisely things as they are—simple and not variegated, exempt from change and therefore stable objects of knowledge. Plato's own assumption of this position perhaps reflects certain confusions about the knowability of things that change; one should not, however, on that ground exclude this aspect of the concept of reality from metaphysical thought in general. Ultimate reality, whatever else it is, is genuine as opposed to sham. Second, reality is original in contrast to derivative, self-dependent rather than dependent on the existence of something else. When Aristotle sought to inquire into the most real of all things, or when medieval philosophers attempted to establish the characteristics of what they called the ens realissimum (“the most real being”), or the original and perfect being, they were looking for something that, in contrast to the everyday things of this world, was truly self-contained and could accordingly be looked upon as self-caused. Likewise, the 17th-century Rationalists (Rationalism) defined substance as that which can be explained through itself alone. Writers like René Descartes and Benedict de Spinoza were convinced that it was the task of the metaphysician to seek for and characterize substance understood in this sense; the more mundane substances with which physical scientists were concerned were, in their opinion, only marginally relevant in this inquiry. Third, and perhaps most important, reality for the metaphysician is intelligible as opposed to opaque. Appearances are not only deceptive and derivative, they also make no sense when taken at their own level. To arrive at what is ultimately real is to produce an account of the facts that does them full justice. The assumption is, of course, that one cannot explain things satisfactorily if one remains within the world of common sense, or even if one advances from that world to embrace the concepts of science. One or the other of these levels of explanation may suffice to produce a sort of local sense that is enough for practical purposes or that forms an adequate basis on which to make predictions. Practical reliability of this kind, however, is very different from theoretical satisfaction; the task of the metaphysician is to challenge all assumptions and finally arrive at an account of the nature of things that is fully coherent and fully thought-out.

      It should be obvious that, to establish his right to pronounce on what is ultimately real in the sense analyzed, the metaphysician has a tremendous amount to do. He must begin by giving colour to his claim that everyday ways of thinking will not suffice for a full and coherent description of what falls within experience, thus arguing that appearances are unreal—although not therefore nonexistent—because they are unstable and unintelligible. This involves a challenge to the final acceptability of such well-worn ideas as time and space, thing and attribute, change and process—a challenge that metaphysicians have not hesitated to make, even though it has been treated with skepticism both by ordinary men and by some of their fellow philosophers (e.g., G.E. Moore, a 20th-century British thinker who has greatly influenced modern Analytic philosophy). Second, granted that there are contradictions or incoherences in the thought of common sense, the metaphysician must go on to maintain that they cannot be resolved by deserting common sense for science. He will not deny that the concepts of science are in many respects different from those of everyday thought; to take one aspect only, they are altogether more precise and sharply defined. They permit the scientist to introduce into his descriptions a theoretical content that is lacking at the everyday level and in so doing to unify and render intelligible aspects of the world that seem opaque when considered singly. The metaphysician will argue, however, that this desirable result is purchased at a certain price: by ignoring certain appearances altogether. The scientist, in this way of thinking, does not offer a truer description of the phenomena of which ordinary thought could make no sense but merely gives a connected description of a selected set of phenomena. The world of the scientist, restricted as it is to what can be dealt with in quantitative terms, is a poor thing in comparison with the rich if untidy world of everyday life. Alternatively, the metaphysician must try to show that scientific concepts are like the concepts of common sense in being ultimately incoherent. The premises or presuppositions that the scientist accepts contain unclarities that cannot be resolved, although they are not so serious as to prevent his achieving results that are practically dependable. Many ingenious arguments on these lines have been produced by philosophers, by no means all of whom could be said to be incapable of a true understanding of the theories they were criticizing. (Leibniz, for example, was a physicist of distinction as well as a mathematician of genius; G.W.F. Hegel, a 19th-century German Idealist, had an unusual knowledge of contemporary scientific work; and Alfred North Whitehead, a pioneer of 20th-century metaphysics in the Anglo-Saxon world, was a professor of applied mathematics, and his system developed from physics and contained a wealth of biological ideas.) The fact remains, nevertheless, that few if any practicing scientists have been seriously troubled by such arguments.

      Even if the metaphysician were thus able to make good the negative side of his case, he would still face the formidable difficulty of establishing that there is something answering to his conception of what is ultimately real and of identifying it. The notion of an original being, totally self-contained and totally self-intelligible, may not itself be coherent, as the 18th-century British philosopher David Hume and others have argued; alternatively, there may be special difficulties in saying to what it applies. The fact that different metaphysicians have given widely different accounts of what is ultimately real is certainly suspicious. Some have wanted to say that there is a plurality of ultimately real things, others that there is only one; some have argued that what is truly real must be utterly transcendent of the things of this world and occupy a supersensible realm accessible only to the pure intellect, while others have thought of ultimate reality as immanent in experience (the Hegelian Absolute, for example, is not a special sort of existent, but the world as a whole understood in a certain way). That metaphysical inquiry should issue in definitive doctrine, as so many of those who engaged in it said that it would, is in these circumstances altogether too much to hope for.

The science of the world as a whole
      Another way in which metaphysicians have sought to define their discipline is by saying that it has to do with the world as a whole.

      The implications of this phrase are not immediately obvious. Clearly, a contrast is intended in the first place with the various departmental sciences, each of which selects a portion or aspect of reality for study and confines itself to that. No geologist or mathematician would claim that his study is absolutely comprehensive; each would concede that there are many aspects of the world that he leaves out, even though he covers everything that is relevant to his special point of view. By contrast, it might be supposed that the metaphysician is merely to coordinate the results of the special sciences. There is clearly a need for the coordination of scientific results because scientific research has become increasingly specialized and departmentalized; individual scientific workers need to be made aware of what is going on in other fields, sometimes because these fields impinge on their own, sometimes because results obtained there have wider implications of which they need to take account. One can scarcely see metaphysicians, however, or indeed philosophers generally, performing this function of intellectual contact man in a satisfactory fashion. It might then be supposed that their concern with the world as a whole is to be interpreted as a summing up and synthesizing of the results of the particular sciences. Plato spoke of the philosopher as taking a synoptic view, and there is often talk about the need to see things in the round and avoid the narrowness of the average specialist, who, it is said, knows more and more about less and less. If, however, it is a question of looking at scientific results from a wider point of view and so of producing what might be called a scientific picture of the world, the person best qualified for the job is not any philosopher but rather a scientist of large mind and wide interests. Metaphysics cannot be satisfactorily understood as an account of the world as a whole if that description suggests that the metaphysician is a sort of superscientist, unlimited in his curiosity and gifted with a capacity for putting together other people's findings with a skill and imagination that none of them individually commands. Only a scientist could hope to become such a superscientist.

      More hope for the metaphysician can be found, perhaps, along the following lines. People want to know not only what the scientist makes of the world but also what significance to assign to his account. People experience the world at different levels and in different capacities: they are not only investigators but also agents; they have a moral and a legal, an aesthetic and a religious life in addition to their scientific life. Man is a many-sided being; he needs to understand the universe in the light of his different activities and experiences. There are philosophers who appear to find no problem here; they argue that there can be no possibility of, say, a moral or a religious vision of the world that rivals the scientific vision. In this view, morals and religion are matters of practice, not of theory; they do not rival science but only complement it. This neutralist attitude, however, finds little general favour; for most thinking people find it necessary to choose whether to go all the way with science, at the cost of abandoning religion and even morals, or to stick to a religious or moral world outlook even if it means treating scientific claims with some reserve. The practice of the moral life is often believed to proceed on assumptions that can hardly be accepted if science is taken to have the last word about what is true. Accordingly, it becomes necessary to produce some rational assessment of the truth claims of the different forms of experience, to try to think out a scheme in which justice is done to them all. Many familiar systems of metaphysics profess to do just that; among others there are Materialism, which favours the claims of science; Idealism, which sees deeper truth in religion and the moral life; and the peculiar dualism of the 18th-century German philosopher Immanuel Kant (Kant, Immanuel), which holds that science gives the truth about phenomena, while reserving a noumenal (noumenon), or supersensible, sphere for moral agency.

      This conception of metaphysics as offering an account of the world or, as is more often said, of experience as a whole, accords more obviously with the position of those who see ultimate reality as immanent, or inherent in what is immediately known, than of those who take it to be transcendent, or beyond the limits of ordinary experience. It is possible, in fact, to subscribe to the legitimacy of metaphysics as so understood without postulating the existence of any special entities known only to the metaphysician—a claim that plain men have often taken to connect metaphysics with the occult. This is not to say, of course, that metaphysical problems admit of easy solutions when understood along these lines. There is a variety of widely different ways of taking the world as a whole: depending on which aspect or aspects of experience the individual metaphysician finds especially significant; each claims to be comprehensive and to confute the claims of its rivals, yet none has succeeded in establishing itself as the obviously correct account. Even systems that are widely condemned as impossible, such as Materialism, turn out in practice to command constantly renewed support as new discoveries in the sciences suggest new ways of dealing with old difficulties. A cynic might take such facts as meaning that people subscribe to theories of this sort more as a matter of emotional than of rational conviction; metaphysics, as Bradley (Bradley, F H) remarked with surprising frankness, consists in the finding of bad reasons for what one believes upon instinct.

The science of first principles
      Another phrase used by Bradley in his preliminary discussion of metaphysics is “the study of first principles,” or ultimate, irrefutable truths.

      Metaphysics could be said to provide a theory of first principles if it furnished men with a set of concepts in the light of which they could arrive at the connected account of experience as a whole just spoken of, and the two descriptions of the subject would thus be two sides of a single coin. The idea that metaphysics has to do with first principles, however, has wider implications.

      The term “first principles” is a translation of the Greek word archai. An arche is something from which an argument proceeds—it can be either a primary premise or an ultimate presupposition. Plato, in a famous passage in Politeia (The Republic), contrasted two different attitudes to archai: namely that of the mathematician (mathematics, philosophy of), who lays down or hypothesizes certain things as being true and then proceeds to deduce their consequences without further examining their validity; and that of the dialectician (dialectic), who proceeds backward, not forward, from his primary premises and then seeks to ground them in an arche that is not hypothesized at all. Unfortunately, no concrete details exist of the way in which Plato himself thought this program could be carried out; instead he spoke of it only in the most general terms. The suggestion, nevertheless, that metaphysics is superior to any other intellectual discipline in having a fully critical attitude toward its first principles is one that still continues to be made, and it needs some examination.

 As regards mathematics, for example, it might be said that mathematicians could be uncritical about the first principles of their science in the following ways: (1) They might take as self-evidently true or universally applicable some axiom or primary premise that turned out later not to possess this property. (2) They might assume among their first principles certain propositions about existence—to the effect that only certain kinds of things could be proper objects of mathematical inquiry (rational as opposed to irrational numbers, for example)—and time might indeed reveal that the assumption was inappropriate. The remedy for both sorts of error, however, is to be found within the realm of mathematics itself; the development of the discipline has consisted precisely in eliminating mistakes of this kind. It is not clear even that the discovery and removal of antinomies in the foundations of mathematics is work for the metaphysician, although philosophically minded persons like Gottlob Frege (Frege, Gottlob), a German mathematician and logician, and Bertrand Russell (Russell, Bertrand), perhaps the best known English philosopher of the 20th century, have been much concerned with them. The situation is not fundamentally different when the empirical sciences are considered. Admittedly, the exponents of these sciences give more hostages to fortune insofar as they have to assume from the first the general correctness of the results of other disciplines; there can be no question of their checking on these for themselves. Mathematicians, too, begin by assuming the validity of common argument forms without making any serious attempt to validate them, and there is nothing seriously wrong with their proceeding in this manner. If confidence in bad logic has sometimes been responsible for holding up mathematical advance, bolder mathematicians have always known in practice that the right thing to do is to let the argument take them wherever it will on strictly mathematical lines, leaving it to logicians to recognize the fact and adjust their theory at their convenience.

      It thus seems that the assertion that a special science like mathematics is uncritical about its archai is false; there is a sense in which mathematicians are constantly strengthening their basic premises. As regards the corresponding claim about metaphysics, it has at one time or another been widely believed (1) that it is the business of metaphysics to justify the ultimate assumptions of the sciences, and (2) that in metaphysics alone there are no unjustified assumptions. Concerning (1), the question that needs to be asked is how the justification is supposed to take place. It has been argued that the metaphysician might, on one interpretation of his function, be said to offer some defense of science generally by placing it in relation to other forms of experience. To do this, however, is not to justify any particular scientific assumptions. In point of fact, particular scientific assumptions get their justification, if anywhere, when a move is made from a narrower to a more comprehensive science; what is assumed in geology, for example, may be proved in physics. But this, of course, has nothing to do with metaphysics. The difficulty with (2) is that of knowing how any intellectual activity, however carefully conducted, could be free of basic assumptions. Some metaphysicians (such as Bradley and his Scottish predecessor J.F. Ferrier (Ferrier, James Frederick)) have claimed that there is a difference between their discipline and others insofar as metaphysical propositions alone are self-reinstating. For example, the Cartesian proposition cogito (cogito, ergo sum), ergo sum (“I think, therefore I am”) is self-reinstating: deny that you think, and in so doing you think; deny that you exist, and the very fact gives proof of your existence. Even if it could be made out that propositions of this kind are peculiar to metaphysics, however, it would not follow that everything in metaphysics has this character. The truth is, rather, that no paradox is involved in denying most fundamental metaphysical claims, such as the assertion of the Materialist that there is nothing that cannot be satisfactorily explained in material terms or the corresponding principle of Aristotle that there is nothing that does not serve some purpose.

      The view that metaphysics, or indeed philosophy generally, is uniquely self-critical is among the myths of modern thought. Philosophers rely on the results of other disciplines just as other people do; they do not pause to demonstrate the legitimacy of the principles of simple arithmetic before entering on calculations in the course of their work, nor do they refrain from employing the reductio ad absurdum type of refutation (i.e., showing an absurdity to which a proposition leads when carried to its logical conclusion) until they have assured themselves that this is a valid way of confuting an opponent. Even in their own field they tend, like painters, to work within traditions set by great masters rather than to think everything out from scratch for themselves. That philosophy in practice is not the fully self-critical activity its exponents claim it to be is shown nowhere more clearly than in the reception that philosophers give to theories that are unfashionable; they more often subject them to conventional abuse than to patient critical examination. It is, nevertheless, from the conviction that philosophy, and especially metaphysical philosophy, operates without unjustified assumptions that current claims about the superiority of this branch of thinking derive their force. This conviction connects with the views already mentioned, that metaphysics is the science of first principles and that the principles in question are ineluctable in the sense that they are operative in their own denial.

Metaphysics and other branches of philosophy
      It may be useful at this point to consider the relations of metaphysics to other parts of philosophy. A strong tradition, derided by Kant, asserted that metaphysics was the queen of the sciences, including the philosophical sciences. The idea presumably was that those who worked within fields such as logic and ethics, as well as physicists and biologists, proceeded on assumptions that in the last resort had to be approved or corrected by the metaphysician. Logic could be conceived as a special study complete in itself only if the logician were allowed to postulate a correspondence between the neat and tidy world of propositions, which was the immediate object of his study, and the world existing in fact; metaphysics might and sometimes did challenge the propriety of this postulate. Similarly, ethics, like law, could get nowhere without the assumption that the individual agent is a self-contained unit answerable in general terms for what he does; metaphysics had the duty of subjecting this assumption to critical examination. As a result of such claims it was widely believed that any results obtained by logicians or ethicists must at best be treated as provisional; followers of Hegel (Hegelianism), who advanced these claims with passionate conviction, were inclined in consequence to regard logic and ethics alike as minor branches of philosophy. It has been a feature of 20th-century philosophical thought, especially in Britain and the United States, to dispute these Hegelian contentions and argue for the autonomy of ethics and logic; that is, for their independence of metaphysics. Thus, formal logicians of the school of Frege and Russell were apt to claim that the principles of logic applied unequivocally to all thinking whatsoever; there could be no question of their having to await confirmation, still less correction, from the metaphysician. If metaphysical arguments suggested that fundamental laws of logic such as the principle of noncontradiction—that a statement and its contradictory cannot both be true—might not be in order, the only conclusion to draw was that such arguments must be confused: without observation of the laws of logic there could be no coherent thinking of any sort.

 Similarly, G.E. Moore (Moore, G E), in a celebrated section of his Principia Ethica (1903), tried to show that statements like “This is good” are sui generis and cannot be reduced to statements of either natural or metaphysical fact; the Idealist belief that ethics ultimately depends on metaphysics rested on a delusion. Moore perhaps failed to see the force of the Idealist challenge to the individualist assumptions on which much ethical thinking proceeds, and he did not note that, in one respect at least, ethical results can be dependent on those of metaphysics: if metaphysics shows that the world is other than it is initially taken to be, conclusions about what to do must be altered accordingly. Again, the reaction among logicians to Hegelian attempts to merge logic into metaphysics certainly went too far. There is a genuine philosophical problem about the relation between the world of logic and the world of fact, and it cannot be solved by simply repeating that logic is an autonomous discipline whose principles deserve respect in themselves. None of this, however, shows that metaphysics is the fundamental philosophical discipline, the branch of philosophy that has the last word about what goes on in all other parts of the subject.

Metaphysics and analysis (analytic philosophy)
      Modern British and American philosophers commonly describe themselves as engaged in philosophical analysis, as opposed to metaphysics. The interests of a metaphysician, according to this view, are predominantly speculative; he wants to reveal hitherto unknown facts about the world and on that basis to construct a theory about the world as a whole. In so doing he is necessarily engaged in activities that rival those of the scientist, with the important difference that scientific theories can be brought to the test of experience, whereas metaphysical theories cannot. Eschewing this conception of philosophy as impossible, the critic of metaphysics believes that philosophy should confine itself to the analysis of concepts (concept), which is a strictly second-order activity independent of science and which need involve no metaphysical commitment.

      The notion of analysis in philosophy is far from clear. Analysis on any account is meant to result in clarification, but it is not evident how this result is to be achieved. For some, analysis involves the substitution for the concept under examination of some other concept that is recognizably like it (as Gilbert Ryle (Ryle, Gilbert), an English Analyst, elucidated the concept of mind by replacing it with the notion of “a person behaving”); for others, analysis involves the substitution of synonym for synonym. If the latter understanding of analysis is required, as in Moore's classic example of the analysis of brother as male sibling, not much enlightenment is likely to ensue. If, however, the philosopher is permitted to engage in what is sometimes pejoratively described as “reductive analysis,” he will produce interest at the cost of reintroducing speculation. Ryle's Concept of Mind (1949) is a challenging book just because it advances a thesis of real metaphysical importance—that one can say everything one needs to say about minds without postulating mental substance.

      A further aspect of the situation that deserves mention is this. If it is the case, as is often claimed, that analysis can be practiced properly only when the analyst has no metaphysical presuppositions, by what means does he select concepts for analysis? Would it not be appropriate for him, in these circumstances, to take any concept of reasonable generality as a suitable subject on which to practice his art? It turns out, in fact, however, that the range of concepts commonly recognized as philosophical is more limited than that, and that those concepts to which Analytic philosophers give their attention are chosen because of their wider philosophical bearings. Thus, recent philosophers have paid particular attention to the concept of knowledge not just because it is a notion whose analysis has long proved difficult but also because on one account at least it involves an immediately experienced mental act—something that many Analysts would like to proscribe as mythical. Similarly, the celebrated analysis of the idea of causality (causation) put forward by David Hume (Hume, David) was not undertaken out of idle curiosity but with a wider purpose in mind: to undermine both the Aristotelian and the Cartesian views of the world and to substitute for them an atomism of immediate appearances in which all objects were “loose and separate”—that is, logically independent one of another. The insight into the constitution of nature promised in different ways by Aristotle and Descartes (Descartes, René) was an illusion, the truth being that scientific advance serves only to “stave off our ignorance a little.” What Hume said about causation connects internally with his views about what exists. Despite his polemic against books of “divinity and school metaphysics,” he had a metaphysics of his own to recommend.

      The truth is that metaphysics and analysis are not separate in the way modern Analytic philosophers pretend. The speculative philosophers of the past were certainly not averse to analysis: witness the splendid discussion of the concept of knowledge in Plato's Theaetetus, or, for a more recent example, Bradley's account of the meanings of “self.” The legend that a metaphysical philosopher has his eye so firmly set on higher things that he is entirely careless of the conceptual structure he seeks to recommend is absolutely without foundation. A metaphysical philosopher is a philosopher after all: argument and the passion for clarification are in his blood. Although some contemporary philosophers profess to undertake analysis entirely for its own sake and without explicit metaphysical motivation, it may be doubted if their claim is capable of being sustained. The “logical analysis” practiced by Russell in the early part of the 20th century was not metaphysically neutral, nor was the analysis of the Logical Positivists, who recommended a strongly scientific view of the world. Some current analytic work is motivated less by the desire to forward an overall theory than by a wish to destroy a prevailing or previously held theory that is considered objectionable. To seek to overthrow a metaphysical theory, however, is itself to engage in metaphysics—not very interesting metaphysics, perhaps, but metaphysics all the same.

      It may be added, as a historical note, that the Rationalist (Rationalism) philosophers of the 17th and 18th centuries, who emphasized the predominant role of reason in the construction of a system of knowledge, believed that the philosopher's task fell into two parts. He must first break down complex concepts into their simple parts; this was a matter of analysis. Then he must proceed to show how knowledge of these simples would serve to explain the detailed constitution of things; this would involve synthesis. That there are deep obscurities in this program—e.g., whether it is a matter of analyzing concepts or getting down to the simplest elements of things—is less important in the present context than that analysis and synthesis were thus taken to be complementary. The classical statement of this point of view is to be found in Descartes's Discours de la méthode (1637; Discourse on Method), with the corresponding passages in the Regulae ad Directionem Ingenii (published posthumously 1701; Rules for the Direction of the Mind). That the idea persisted well into the 18th century is evidenced by the remarks made by Kant in his essay Untersuchung über die Deutlichkeit der Grundsätze der natürlichen Theologie und der Moral (1764; Inquiry into the Distinctness of the Principles of Natural Theology and Morals), in which he said that metaphysics was not yet in a position to pass beyond the stage of analysis to that of synthesis. He did not mean that for the time being philosophy must remain entirely nonmetaphysical, in the way some moderns suppose it can, but rather that it needs to go on elaborating a conceptual scheme, which, however, cannot be used constructively until it is complete. Actually, Kant belied his own professions at the time insofar as he thought himself in possession of a definitive proof of God's existence, which he explained in his essay Der einzig mögliche Beweisgrund zu einer Demonstration des Daseyns Gottes (1763; “The Only Possible Ground for a Demonstration of the Existence of God”). This, however, only illustrates the not very surprising fact that philosophers are often less clear about the nature of their own activities than they think.

Problems in metaphysics
      To give a comprehensive account of the main problems of metaphysics in the space of a few pages is clearly quite impossible. What follows is necessarily highly selective and to that extent misleading; it, nevertheless, attempts to offer an introduction to metaphysical thinking itself rather than reflection on the nature of metaphysics.

The existence of forms, categories, and particulars
Forms (form)
      The early Greek philosophers asked the question ti to on, “What is existent?” or “What is really there?” They originally interpreted this as a question about the stuff out of which things were ultimately made, but a new twist was given to the inquiry when Pythagoras, in the late 6th century BC, arrived at the answer that what was really there was number. Pythagoras conceived what is there in terms not of matter but of intelligible structure; it was the latter that gave each type of thing its distinctive character and made it what it was. The idea that structure could be understood in numerical terms was probably suggested to Pythagoras by his discovery that there are exact correlations between the lengths of the strings of a lyre and the notes they produce. By a bold extrapolation he seems to have surmised that what held in this case must hold in all cases.

      The Pythagorean theory that what is really there is number is the direct ancestor of the Platonic theory that what is really there is Forms, or Ideas (eidē, or ideai). Plato's Forms were also intelligible structures and not material elements, but they differed from Pythagorean numbers by being conceived of as separately existent. There was, as Plato put it, a “place accessible to the intelligence,” which was the place, or realm, of Forms. Each Form was a genuine existent, in the sense of being precisely what it pretended to be; the Form of Beauty, for example, was beautiful through and through. By contrast, the many particular things that partook of or resembled what was truly beautiful were one and all defective. However beautiful any one of them might be, it was also in another respect lacking in beauty. It turned out to possess contradictory characteristics, and as such could never be identified with true reality.

      Plato had taken over from his predecessor Heracleitus, who flourished at about the beginning of the 5th century BC, the doctrine that the world of sensible things is a world of things in constant flux; as he put it in the Theaetetus, nothing is in this world because everything is in a state of becoming something else. Forms were needed to provide stable objects for knowledge as well as to answer the question of what is ultimately real. Although Plato played down the reality of sensible things, making them mere objects of opinion and describing them as falling between what is and what is not, he did not deny their existence. It was not his thesis that Forms alone exist. On the contrary, he appears to have held that God (who was certainly not a Form) had somehow fashioned the physical world on the model of the Forms, using space as his material. This is the description that is given in the Timaeus, in a passage that Plato perhaps meant his readers not to take quite literally but that stated his view as plainly as he thought it could be stated. In this passage God appears in the guise of the “ Demiurge,” although he is referred to freely in other Platonic dialogues. Souls were also distinct from Forms in Plato's thought.

 In the discussions that developed around the theory of Forms, many difficulties were revealed, most of them familiar to Plato himself. The question of how the one Form was supposed to relate to the many particulars that participated in or resembled it was nowhere satisfactorily answered. The difficulty turned on how the Form was to be thought of at once as an existent and as a structure. Plato seemed on occasion to think of it as a structure hypostatized, or given real existence. This thesis led to the antinomies exposed in the “third man” argument. According to this theory, particular men were alleged to be human because of their relationship to “Man himself”; i.e., the Form of man. But whence did the latter derive its nature? Must there not be a second Form to explain what the first Form and its particulars have in common, and will not this generate an infinite regress? Again, the problem of the precise population of the world of Forms never got a definitive solution, perhaps because the theory of Forms was put to more than one purpose. Sometimes it was said that there is a Form corresponding to every general word, but elsewhere the theory was that what is merely negative (e.g., lifeless) has no need of a special Form, nor does what is manufactured. There is even a question as to whether trivial everyday things such as mud and hair and dirt have Forms, though it is agreed that there is a Form of man.

      The problems just referred to were stated trenchantly in Plato's dialogue the Parmenides; the discussion there ends with the statement that the Forms must be retained if an account of intelligible discourse is to be given, but no indication is offered as to how the theory is to be refurbished. Some Platonic scholars have inferred that Plato virtually gave it up, but such evidence as there is suggests that he only transformed it into a theory of Form-numbers, more openly Pythagorean than the earlier version. There are many references in Aristotle to this theory of Form-numbers, but no writing of Plato's own on the subject has survived, and it is virtually impossible at this late stage to say what this theory really comprised.

      One further feature of the theory of Forms must be mentioned here: the view that there is a supremely important Form, the Form of goodness, or of the Good, which somehow determines the contents of the world of Forms and brings order into it. In a celebrated but brief and tantalizing passage in Politeia, the Form of the Good is spoken of as being to the intelligible realm what the sun is to the visible realm; just as the sun makes living things grow and renders them visible, so the Good is responsible for the existence and intelligibility of Forms, though it is itself “on the other side of Being.” This passage had a tremendous historical influence on the Neoplatonists (Neoplatonism), who saw it as anticipating the ultimate ineffable reality—the One, from which everything describable was in some way an emanation—in which they came to believe. It seems possible, however, that Plato had no such mystical thoughts in mind but simply wanted to say that the world of Forms is ordered through and through, everything in it being there for a purpose. The Form of Good is, in fact, the counterpart of the nous (Mind) of Anaxagoras, another of Plato's predecessors, which was supposed to arrange everything for the best.

Categories (category) and universals (universal)
 The most famous critic of Plato's theory of Forms was Aristotle, who devised his doctrine of categories largely to counter it. According to this doctrine, “being is spoken of in many ways”: one can say that there are such things as individual horses, but one can also say that there is such a thing as being a horse, or as being upside down. Expressions can be classified under various heads: predicates signify substances (e.g., “man” or “horse”), qualities (e.g., “white”), relations (e.g., “greater”), quantities (e.g., “three yards long”), time (e.g., “last year”), and so on—sometimes Aristotle listed ten categories, sometimes only eight. The kind of being that any predicate possesses, however, is derivative in comparison with the being of an individual substance, a particular man or a particular horse. It is such things that exist in the primary sense, and it is upon their existence that the existence of other types of being depends. Or, to put the point in not quite Aristotelian terms, primary substances are the only concrete existents; Socrates, the bearer of a proper name, exists in a way in which humanity or whiteness or being greater do not. The latter are really no more than abstractions, and nothing but confusion can arise from neglecting that fact.

      Mention has already been made of the difficulties into which this doctrine led when it came to describing primary substances; it appeared that these entities could not be characterized but only named or pointed to, a conclusion accepted much later by Ludwig Wittgenstein (Wittgenstein, Ludwig), a 20th-century philosopher, in his Tractatus Logico-Philosophicus and by Russell in his lectures on logical atomism. These difficulties, however, were not seen at the time the theory was promulgated, and it is more important here to emphasize the fact that it undermined any doctrine of the Platonic type. To argue that Forms, or numbers, alone are real is to argue for the reality of abstractions; to put the point succinctly, beauty exists only so long as something is beautiful, and that something must be a concrete individual. Or if this is not quite true (for, after all, it could be said that there is such a thing as having a million sides even if nothing in fact has a million sides), concrete existence must precede abstract existence in some cases at least: the “x” in “x is red” must sometimes be replaceable by an actual rather than a merely possible entity.

      A prominent subject of philosophical discussion in the Middle Ages was what came to be known as the problem of universals, which concerned the ontological status, or type of existence, to be assigned to the referents of general words. One of Plato's critics had said, “I see particular horses, but not horseness”; and Plato had answered, “That is because you have eyes but no intelligence.” There can be no doubt that Plato thought that horseness, the Form of horse, or Horse itself, to use his own expression, was something that existed separately; it could be discerned not by the bodily eyes but by the eye of the soul. The view that besides individual horses there also exists the Form of horse was known in the Middle Ages as realism. Aristotle was also alleged to be a Realist, because he too thought that Forms were really there, although only as embodied in particular instances. More skeptical philosophers denied the reality of universals altogether, some identifying them with thoughts (conceptualists), others with mere names (nominalists) (nominalism).

      The dispute about universals was in fact very confused. At least two quite separate issues were involved. First of all, there was the question about the status to be assigned to whatever it was that predicates referred to; this question seemed urgent just because, for example, geometricians (geometry) were able to discuss the properties of the triangle or the circle. What and where were the triangle and the circle? In fact, the Aristotelian doctrine of categories had already indicated that the being of any predicate was necessarily different from that of primary substances; the circle did not and could not exist as this man or this horse did. When Aristotle is described as a Realist in the dispute about universals, the description is very misleading. In one sense he did not believe that universals are real at all; in another sense, however, he did, and this is where the second issue arose. Some people who denied the reality of universals wanted to say that all classification is artificial; the descriptions men give of things depend upon their interests as much as upon what is really there. Aristotle, by contrast, believed in a doctrine of natural kinds; he thought that every particular horse, for example, embodied the form or objective essence of horse, which was accordingly a genuine, if abstract, constituent of the world. The question of the extent to which classification is artificial is clearly quite different from that of the status of universals; it remains to be answered even if the latter problem is dismissed, as it is by modern philosophers who say that only proper names and individuating phrases have referents; general words do not. These differences, however, were not clearly seen either in the Middle Ages or during the 17th century, when the whole question was discussed at length by philosophers such as Thomas Hobbes and John Locke.

Basic particulars
      In discussions of the problem of universals, it was frequently claimed, especially by nominalists, that only particulars exist. The notion of a particular is in many respects unclear. Strictly speaking, the terms particular and universal are correlatives; a particular is an instance of universal (for example, this pain, that noise). It would seem from this that particulars and individuals should be the same, but there are writers who distinguish them. Bradley, in his Principles of Logic (1883), treated particulars as mere momentary instantiations of universals and contrasted them with individuals as continuants possessing internal diversity. An individual can be not merely identified but also re-identified; because it lasts through time, it may possess incompatible attributes at different periods of its history. A particular, on the other hand, is nothing but an instantiation of an attribute and as such must possess that attribute if it is to be anything. Similarly, a particular can be met with once, but not again; as time moves on, it passes out of existence and is replaced by another particular that may resemble it but is not literally identical with it.

      If particulars and individuals are thus distinguished, it is by no means clear that only particulars exist, or indeed that they exist at all; it could be that they are no more than abstract aspects of genuinely concrete entities such as persons or material things. But there are arguments on the other side, advanced in a variety of forms by David Hume and Bertrand Russell. Hume believed that the ultimate constituents of the world were either impressions or their fainter copies, ideas; both were species of perceptions (perception). Impressions he defined as “internal and perishing existences”; they were of various kinds, embracing feelings as well as such things as experienced colours and smells, but all were at best extremely short-lived. Impressions arose in human consciousness from unknown causes; their existence could not, however, be denied. By contrast, the existence of continuing and independent material objects and of continuing minds was extremely precarious; analysis showed both to be no more than bundles of perceptions, united by certain relations, and Hume more than once referred to them as “fictions,” although it turned out on examination that they were not fictions in the way ghosts are. Hume's reasons for advancing these views were primarily epistemological; he thought that statements about continuants were all open to doubt, although statements about the contents of immediate experience could not be challenged. When it was a question of what really existed, the only sure answer was items in consciousness—namely, impressions and ideas.

      Russell, who was generally sympathetic to this answer, added another argument derived from logic: proper names, he said, were names of particulars, which must accordingly exist. Ordinary proper names (such as “Socrates”) had other functions than to denote, but logically proper names (“this” was Russell's example) served simply to pick out objects of immediate acquaintance. Russell was apparently unabashed by the consequence that such objects would be both private to the experience of particular persons and of very brief duration; he thought his doctrine of “logical constructions,” which allowed for “inferred entities” on the basis of what is immediately certain, would provide the publicity and continuity necessary to do justice to actual experience. These assumptions, however, have met with serious criticism. P.F. Strawson (Strawson, Sir Peter), a British philosopher whose thought centres on the analysis of the structure of ordinary language, especially in his Individuals: An Essay in Descriptive Metaphysics (1959), not only attacked Russell's account of proper names but argued that experience demands a framework of basic particulars that are not Russell's momentary private objects but continuing public existents—in fact, individuals in the terminology explained above. If experience consisted of nothing but sounds, the minimum prerequisite of intelligibility would be that there should be a continuing master sound, an analogue in this medium of continuing material substance in the material order. Without such basic particulars as continuing material things, identification and reidentification would be impossible. Strawson conceded that persons as well as things were genuine continuants, but maintained all the same that the hypothesis that reality might consist of nothing but minds was quite untenable. Minds are no more than aspects of persons, and persons have bodies as well as minds. Strawson agreed that disembodied existence was logically possible, but added that such existence would make no sense except as a survival of embodied existence in a common public world.

      If this is correct, what exists cannot consist, as Hume supposed, of momentary items but must rather take the form of substances in the Aristotelian sense. These act as basic particulars in the actual intellectual scheme men adopt. Strawson, however, was not content merely to assert this fact; he wanted to argue that things must be like this if reference and description in their familiar form are to be possible at all. His main theory, which plainly owes a debt to Kant as well as to Wittgenstein, was worked out with primary reference to the physical world. It would be interesting to know if an examination of social reality would yield comparable results: whether individual persons or something larger—continuing societies or institutions—should be taken as basic particulars in that sphere. Many philosophers assert dogmatically that a society is nothing but an aggregate of its individual members. Nevertheless, men are members of society in virtue of their performance of a number of social roles, and role itself is a concept that makes sense only if the notion of society is presupposed. In one sense, a society is nothing apart from its members; remove them, and it would disappear. Equally, however, the members themselves are what they are because of their various roles; it is arguable that they would be nothing apart from their social relations. Hence, the force of Bradley's remark is evident, namely, that “the ‘individual' apart from the community is not anything real.”

      It remains to add here that a number of philosophers have tried to argue that the basic items in reality should be described not as substances but in some other terms. Russell (Russell, Bertrand) at one stage in his career spoke of the world as consisting of events (event); his former colleague A.N. Whitehead (Whitehead, Alfred North) made the notion of process (process philosophy) central in his metaphysics. Developments in modern physics undoubtedly lend a certain plausibility to these and similar views. Yet it remains difficult to understand what an event could be in which nothing was concerned, or how there could be a process in which nothing was in process. Event and process, in fact, are expressions that belong to derivative categories in the general Aristotelian scheme; like all other categories, they depend on the category of substance. If the latter is removed, as these metaphysicians propose to remove it, it is hard to know what is left.

The existence of God
 Perhaps the most celebrated issue in classical metaphysics concerned the existence of God. God in this connection is the name of “the perfect Being” or “the most real of all things”; the question is whether it is necessary to recognize the existence of such a being as well as of things that either are or might be objects of everyday experience. A number of famous arguments have been advanced from the time of the Greeks in favour of the thesis that such a recognition is necessary. The neatest and most ingenious was the a priori argument of St. Anselm (Anselm of Canterbury, Saint) in the 11th century, who said that “that than which nothing greater can be conceived” must exist in fact as well as in thought, for if it existed only in thought and not in fact, something greater than it could be conceived, namely the same thing existing in fact. God necessarily exists, because the idea of God is the idea of that than which nothing greater can be conceived. This is the argument later known as the ontological proof. Relatively few philosophical theologians, either in the Middle Ages or later, could bring themselves to accept this bold piece of reasoning (although Descartes, Spinoza, Leibniz, and Hegel (Hegel, Georg Wilhelm Friedrich) all accepted it in principle); most preferred to ground their case for God's existence on premises that claimed to be empirical. Thus, St. Thomas Aquinas (Aquinas, Thomas, Saint), perhaps the most influential Scholastic philosopher, in the 13th century argued that to explain the fact of motion in the world, the existence of a prime mover must be presupposed; that to account for contingent or dependent being the existence of something that is necessary or self-contained must be presumed; that to see why the world is orderly and why the different things in it fit together harmoniously, a situation that might not have obtained, a Creator who fashioned it on these lines must be postulated—adding in each case “and this all men call ‘God'.” These are versions of the first cause argument and the argument from design, which were to figure prominently in the thinking of later theistically inclined metaphysicians.

      The first cause argument should, perhaps, be examined in somewhat greater detail, because it both has an immediate plausibility and lies at the basis of many different kinds of metaphysical systems (that of Hegel, for example, as well as that of Aquinas). The argument begins with the innocent-looking statement that something contingent exists; it may be some particular thing, such as oneself, or it may be the world in general (thus, the description of the proof as being a contingentia mundi, or “from the contingency of the world”). In describing oneself or the world as contingent, one means only that the thing in question does not exist through itself alone; it owes its being to the activity of some other thing, as a person owes his being to his parents. Contingent things are not self-complete; they each demand the existence of something else if they are to be explained. Thus, the move is made from contingent to necessary being; it is felt that contingent things, of whatever order, cannot be endlessly dependent on other contingent things but must presuppose a first cause that is self-complete and so exists necessarily. In Hegel the necessary being is not a separate existent but, as it were, an order of things; the loose facts of everyday life and even of science are said to point to a system that is all-embracing and in which everything is necessarily what it is. The principle of the argument, however, is unchanged despite the change in the conclusion.

      Damaging criticism was brought against all the traditional arguments for God's existence by Hume and Kant in the 18th century. The ontological proof was undermined by the contention that “being is not a real predicate”; existence is not part of the concept of God in the way in which, for example, being all-powerful is. To say that something exists is not to specify a concept further but to claim that it has an instance; it cannot be discovered whether a concept has an instance by merely inspecting it. The first cause argument, it was contended, suffers from two fatal weaknesses. Even if it is correct in its assertion that contingent being presupposes necessary being, it cannot identify the necessary being in question with God (as happened in each of the Thomistic proofs) without resurrecting the ontological argument. If it is true, as supporters of the causal proof suppose, that God alone can answer the description of a necessary being, then whatever exists necessarily is God and whatever is God exists necessarily. Modern supporters of the causal proof have tried to meet this objection by saying that the equivalence is one of concepts, not of concept and existent; the existence of a necessary being is already established in the first part of the argument, and the equivalence in the second part of the argument is between the concept of necessary being and the concept of God. In other words, they distinguish between existence and essence. In the first part of the argument, the existence of a necessary being is proved; in the second part of the argument, the essence of that necessary being is identified with what men call God. Beyond this first contended weakness, however, there are grave difficulties in the move from contingent to necessary existence. Things in the experienced world are causally related, and some account of this relationship can be given in terms of the temporal relations of events; causal relations hold primarily between kinds of events, and a cause is, at least, a regular antecedent of a specific kind of effect. But when an attempt is made to extend the notion of causality from a relationship that holds within experience to one that connects the experienced world as a whole to something that falls wholly outside it, there is no longer anything firm on which to hold. The activities of God cannot precede happenings in the world because God is, by definition, not in time; and how the relationship is to be understood in these circumstances becomes highly problematic. Some metaphysicians, like some recent theologians, seek to evade the difficulty by saying that God is not the cause of the world but its ground, or again by distinguishing causes of becoming, which are temporal, from a cause of being, which is not. It is doubtful whether these moves do more than restate the problem in different terms.

      The argument from design is itself a form of causal argument and accordingly suffers from all the difficulties mentioned above, together with some of its own, as Hume and Kant both point out. Even on its own terms it is wrong to conclude the existence of a Creator rather than an architect. Furthermore, it infers that the being in question has unlimited powers, when all that the evidence seems to warrant is that its powers are very great. The argument lost much of its force by the publication of the English naturalist Charles Darwin's theory of natural selection. The unbroken reign of law throughout natural evolution is impressive, but as a line of reasoning it does not seem to bear close examination.

      The metaphysical problem of God's existence is more of an issue today than the problem of universals; there are still thinkers who hope to restate the old proofs in more convincing ways. The ontological proof, in particular, has won renewed attention from thinkers such as Norman Malcolm, a philosopher strongly influenced by Wittgenstein, and Charles Hartshorne (Hartshorne, Charles), an American Realist whose form of theism is called panentheism (the doctrine of a God who has an unchanging essence but who completes himself in an advancing experience). Increasingly, however, philosophers of religion are preoccupied not with these metaphysical abstractions but with the status and force of actual religious claims. “The most real of all things” is no longer at the centre of their attention: they seek to investigate God as a suitable object for worship.

The soul, mind, and body (human body)
The soul–body relationship
      As well as believing in the reality of Forms, Plato believed in the immortality of the human soul. The soul was, he thought, an entity that was fundamentally distinct (dualism) from the body although it could be and often was affected by its association with the body, being dragged down by what he called in one passage “the leaden weights of becoming.” The soul was simple, not composite, and thus not liable to dissolution as were material things; further, it had the power of self-movement, again in contrast to material things. Ideally the soul should rule and guide the body, and it could ensure that this situation persisted by seeing that the bodily appetites were indulged to the minimum extent necessary for the continuance of life. The true philosopher, as Plato put it in the Phaedo, made his life a practice for death because he knew that after death the soul would be free of bodily ties and would return to its native element. He also thought that the soul was “akin” to the Forms; it was through the intellect, the purest element in the soul, that the Forms were discovered.

      Plato mentioned and attempted to refute alternative accounts of the relationship of soul and body, including a Pythagorean view that described the soul as an “attunement” of the body and thus tried to explicate it as a form or structure rather than an independently existing thing. A theory of this kind was worked out but not taken to its logical conclusion by Aristotle in his treatise De anima (On the Soul). Aristotle defined soul in terms of functions. The soul of a plant was concerned with nutrition and reproduction, that of an animal with these and with sensation and independent movement, that of a man with all these and with rational activity. The soul was, in each case, the form of some body, and the clear implication of this was that it would disappear as the body in question dissolved. To be more accurate, the soul was the principle of life in something material; it needed the material element to exist, although it was not itself either material or immaterial but, to put it crudely, an abstraction. Even though Aristotle wasclearly committed by everything he said in the earlier parts of the De anima to the view that the soul is not anything substantial, he nevertheless distinguished toward the end of this work between what he called the active and the passive intellects and spoke of the former in Platonic terms. The active intellect was, it appears, separate from the rest of the soul; it came “from outside” and was in fact immortal. It was, moreover, essential to the soul considered as rational, for “without this nothing thinks.” Aristotle thus showed the Platonic side of his thought in the very act of trying to emancipate himself from this aspect of Platonism.

The mind–body relationship (mind–body dualism)
 In more recent metaphysics less has been heard of the soul and more of the mind; the old problem of the relationship of soul and body is now that of the relationship of mind and body. Most, if not all, subsequent discussion of this subject has been affected by the thinking of Descartes. In his Meditationes de Prima Philosophia (1641; Meditations on First Philosophy), he argued that there was a total and absolute distinction between mental and material substance. The defining characteristic of matter was to occupy space; the defining characteristic of mind was to be conscious (consciousness) or, in a broad sense of the term, to think. Material substance was, so to speak, all one, although packets of it were more or less persistent; mental substance existed in the form of individual minds, with God as the supreme example. The mental and the material orders were each complete in themselves, under God; it was this fact that made it appropriate for him to use the technical term substance in this context: mental substance and material substance. The logical consequence of this view, drawn by some later Cartesians, was that there can be no interaction between mind and body; all causality is immanent, within one order or the other, and any appearance of mind affecting body or of body affecting mind must be explained as the result of a special intervention by God, who, on the occasion of changes in one substance, brings it about that there are corresponding changes in the other. Descartes himself, however, had no sympathy with this view, which was called occasionalism. On the contrary, he stated explicitly that he was not in his body as a pilot is in a ship but was “more intimately” bound up with it. Mind could affect body and vice versa because mind and body had a specially close relationship, which was particularly evident in the aspects of conscious life that have to do with sensation, imagination, and emotion as opposed to pure thought.

      Descartes's conviction that, despite their intimate union in this life, mind is really distinct from body sprang from his confidence in the cogito argument (cogito, ergo sum). It was possible, he believed, to doubt the existence of his body (what was certain was only that he had the experience of having a body, and this might be illusory) but not the existence of his mind, for the very act of doubting was itself mental. That mind existed was evident from the immediate testimony of consciousness; that body existed was something that needed an elaborate proof, involving his doctrine of clear and distinct ideas and his attempt to establish the existence of a God who is no deceiver. Apart from this, Descartes appealed to arguments of a broadly Platonic type to bring out what was truly distinctive about mind. He admitted that sensation and imagination could be understood only if referred to the mind–body complex but contended that acts of the pure intellect and of will (here his thought was influenced by that of St. Augustine, the great 5th-century Christian thinker) belonged to the mind as it was in itself. Descartes did not claim to have a philosophical proof of the immortality of the soul—that, in his view, required the assurance of revelation—but he did think that his theory prepared the way for that doctrine by establishing the separate existence of mind.

      The Cartesian account of mind and body had many critics even in Descartes's own day. Hobbes (Hobbes, Thomas) argued that nothing existed but matter in motion; there was no such thing as mental substance, only material substance. Materialism of a sort was also supported by Descartes's correspondent Pierre Gassendi (Gassendi, Pierre), a scientist and Epicurean philosopher. A generation later Spinoza (Spinoza, Benedict de) was to refashion the whole Cartesian metaphysics on bold lines. In place of the two distinct substances, each complete in itself yet each liable to external interference should God will it, Spinoza posited a single substance, God or Nature, possessed of infinite attributes, of which the mental and the material alone are known to men. The “modes,” or manifestations, of this substance were what they were as a result of the necessities of its nature; arbitrary will neither did nor could play any part in its activities. Whatever manifested itself under one attribute had its counterpart in all the others. It followed from this that to every mental event there was a precisely corresponding physical event, and vice versa. A man was thus not a mysterious union of two different elements but a part of the one substance that, like all other parts, manifested itself in different ways under different attributes. Spinoza did not explain why it was that physical events could be correlated with mental events in the case of a human being but not in that of, for example, a stone. His theory of psycho-physical parallelism (psychophysical parallelism), however, has persisted independently of his general metaphysics and has found supporters even in modern times.

      One way in which Spinoza threw fresh light on the mind–body problem was in calling attention to the influence of the body on the mind and in taking seriously the suggestion that they be treated as a single unit. In this respect, his work on the subject was far in advance of the Empiricist (Empiricism) philosophers of the next century. Hume notoriously dismissed Cartesian substance as a “chimera” and argued that minds and bodies alike were nothing but “bundles of perceptions,” interaction between which was always possible in principle; in practice, however, he stuck to the old-fashioned view that mind is one thing and body another and did nothing to explore their actual relationships. Empiricist philosophy of mind, both in Hume and in his successors, such as James Mill, was generally crude; it consisted largely in an attempt to explain the entire life of the mind in terms of Hume's ontology of impressions and ideas. Nor did Kant make much, if any, advance in this particular direction, convinced as he was of the necessity of accepting an empirical dualism of mind and body. It was left to Hegel and the Idealists (Idealism) to look at the problem afresh and to bring out the way in which mental life and bodily life are intimately bound together. The accounts of action and cognition given by T.H. Green and Bradley, and more recently by R.G. Collingwood, are altogether more enlightening than those of Empiricist contemporaries just because they rest on a less dogmatic basis and a closer inspection of fact.

      No metaphysical problem is discussed today more vigorously than that of mind and body. Three main positions are held. First, there are still writers (e.g., H.D. Lewis in his work The Elusive Mind [1969]) who think that Descartes was substantially right: mind and body are distinct, and the “I” that thinks is a separate thing from the “I” that weighs 170 pounds. The testimony of consciousness is invoked as the main support of this conclusion; it is alleged that all men know themselves to be what they are, or at least who they are, apart from their bodily lives; it is alleged again that their bodily lives present themselves as experiences—i.e., as something mental. The existence of mind, as Descartes claimed, is certain, that of body dubious and perhaps not strictly provable. Second, there are writers such as Gilbert Ryle (Ryle, Gilbert) who would like to take the Aristotelian theory to its logical conclusion and argue that mind is nothing but the form of the body. Mind is not, as Descartes supposed, something accessible only to its owner; it is rather something that is obvious in whatever a person does. To put it crudely, mind is simply behaviour (behaviourism). Finally, there are many philosophers who, although more generally sympathetic to the second solution than to the first, wish to provide for an “inner life” in a way in which Behaviourism does not; P.F. Strawson (Strawson, Sir Peter) is a typical example. To this end they try to assert that the true unit is neither mind nor body but the person. A person is something that is capable of possessing physical and mental predicates alike. This is, of course, to say that the “I” that knows simple arithmetic and the “I” that has lost weight recently are the same. How they can be the same, however, has not so far been explained by supporters of this view.

      Aside from these main positions, an interesting development is the stress laid by writers—such as Stuart Hampshire, an “ordinary language” philosopher—on self-activity as the distinguishing characteristic of mind. According to this view, a human being is a body among bodies but is, as Plato said, self-moving as material things are not. That this should be so—that human beings are possessed of wills (free will) and can in favourable circumstances act freely—is taken as an ultimate fact neither requiring nor capable of explanation. It is often denied that any scientific discovery could give rational grounds for questioning this fact. It is also stressed that the causality of a human being is fundamentally different from that of a natural subject, intentional action being quite other than mere behaviour determined from without.

      Connected with these topics is the problem, much discussed in recent philosophy as a result of the rise of cybernetics, of what differentiates men from machines (machine). Two answers used to be given: the power to think and consciousness (artificial intelligence). Now, however, there exist machines whose calculating abilities far surpass those of any human being; such machines may not literally think, but they certainly arrive at conclusions. Furthermore, it is not true that their operations are of a purely routine nature: there is a sense in which they can improve their performance in the light of their “experiences.” They even have an analogue of consciousness in the sensitivity they show to external stimuli. These facts suggest that the gap between minds and machines is less wide than it has often been thought to be; they do not, however, destroy it altogether. Human beings possess powers of creative thought unlike anything found in machines; as Noam Chomsky (Chomsky, Noam), an American linguistics scholar, has stressed (and as Descartes urged in his Discours de la méthode), the ability of human beings to handle language in such a way that they comprehend any one of an infinite number of possible expressions is something that cannot be explained in mechanical terms. Again, as J.R. Lucas, a British philosopher, has argued, human beings have the ability to diagnose and correct their own limitations in a way to which there is no parallel in machines. As some older philosophers put it, man is a being with the power of self-transcendence; he can work within a system, but he can also move to another level and so see the shortcomings of the system. A machine can only work within a system; it operates according to rules but cannot change them of its own accord.

      Finally, mention should be made of an extreme Materialist solution to the mind–body problem: this solution holds that states of mind are in fact states of the brain. Supporters of this theory agree that the two are separate in idea but argue that physiology shows that despite this they are contingently identical. What seems to be a state of mind, above all to its possessor, is really a state of the brain, and mind is thus reduced to matter after all. It is not clear, however, why physiologists should be granted the last word on a topic like this, and, even if it were agreed that they should be, the correlations so far established between mental occurrences and states of the brain are at best sketchy and incomplete. Central-state Materialism (identity theory), as this theory is called, professes to have the weight of contemporary science behind it, but it turns out in fact to have drawn to a remarkable degree on what it thinks will be the science of tomorrow.

Nature and the external world
      The problem of the existence of material things, first propounded by Descartes and repeatedly discussed by subsequent philosophers, particularly those working within the Empiricist tradition, belongs to epistemology, or the science of knowledge, rather than metaphysics; it concerns the question of how it can be known whether there is a reality independent of mind. There are, however, problems about nature and the external world that are genuinely metaphysical.

The reality of material things
      There is first of all the question of the status, or standing, of material things, the kind of being they possess. It has been repeatedly suggested by metaphysical philosophers that the external world is in some way defective in reality, that it is a mere phenomenon, something that seems to be what it is not. Plato, as has already been pointed out, held that objects of the senses generally answered this description; they each appeared to possess characteristics that they could not in fact have (water could not be at once hot and cold) and were to that extent delusive rather than real. There was no stability in the world of phenomena and therefore no true reality. In taking this view, Plato drew no contrast between the world of nature and the world of man, although he undoubtedly believed that souls had a superior status. Leibniz (Leibniz, Gottfried Wilhelm), a later philosopher who also followed this general line of thought, began by explicitly opposing souls to material things. To speak precisely, nothing truly existed except monads (monad), and monads were souls, or spiritual beings: all had perceptions, although these varied enormously in degree of clarity (the perceptions of the monads constituting what is commonly called a stone were singularly faint). Although the final description of the world must thus be given in mental terms, it did not follow that nature as normally perceived is a total illusion. Men perceive as well as think, and, although perception is in fact simply a confused form of thought, it is not for that reason to be set aside altogether. The world of nature, the world of things in space and time, is, as Leibniz put it, a “well-founded phenomenon”; it is what all men must judge to be there, given that they are not pure intellects but necessarily remain to some extent prisoners of their senses.

 A theory on somewhat similar lines was worked out by Kant in the Kritik der reinen Vernunft (1781; Critique of Pure Reason), despite Kant's explicit dissent from Leibniz' account of perception as confused thinking. Kant contrasted a realm of things as they are in themselves, or noumena, with a realm of appearances, or phenomena. The former are unknown, and indeed unknowable, though it seems clear that Kant tended to think of them on lines like those of Leibniz; phenomena do not exist independently but are dependent on consciousness, though not on any one person's consciousness. Kant expressed this position by saying that things phenomenal (phenomenon) are empirically real but transcendentally ideal; he meant that they are undoubtedly there for the individual subject, though when examined from the point of view of critical philosophy, they turn out to be conditioned by the mind through the forms of sensibility and understanding imposed upon them. Kant's most striking argument for this conclusion was that space and time are neither, as the English physicist Sir Isaac Newton (Newton, Sir Isaac) supposed, vast containers inside which everything empirical is situated nor, as Leibniz had suggested, relations between things confusedly apprehended but are rather what he mysteriously called “pure intuitions,” (intuition) factors inherent in the sensibilities of observers. Without observers space and time disappear along with their contents; but once the human point of view is assumed, in the form of percipients who are directly aware of the world through their senses, space and time become as real as anything—indeed, more real because of their pervasive character. There is nothing that falls within experience that does not have temporal relations, and all the data of the senses have spatial relations as well.

      Kant's arguments in support of his revolutionary thesis about space and time unfortunately depend to a large extent on his mistaken philosophy of mathematics, and they have accordingly been discounted by later philosophers. In modern philosophy the issues raised in these discussions survive only in the form of an inquiry into the status of nature as investigated by the natural scientist. Descartes already pointed out that material things in fact have properties different from those they seem to have; they appear to possess secondary qualities such as colour or smell but turn out when thought about strictly to be colourless and odourless lumps of matter occupying and moving about in space. Locke (Locke, John) endorsed this distinction between primary qualities (such as extension, motion, figure, and solidity) and secondary qualities; but George Berkeley (Berkeley, George), a major British Empiricist of the early 18th century, criticized it sharply as absurd: to imagine something that has primary but no secondary qualities is psychologically impossible. For Berkeley the world of the scientist was a fiction and perhaps not even a necessary fiction at that. It seems clear, however, that Berkeley's arguments do not undermine the important distinction between primary and secondary qualities, where the former are treated as fundamental and the latter as derivative; they are valid only against Locke's mistaken claim that primary qualities are objective and secondary qualities subjective. Whatever the explanation, the fact remains that the scientist often knows why the phenomena are as they are, in contrast to the plain man; to that extent nature as he understands it is truer, if not more real, than nature as it is taken to be in everyday experience. Why this should be is not satisfactorily explained by philosophers who follow Berkeley's lead on this question. Nor has either party to the controversy noted sufficiently the extent to which nature as commonly thought of is conceived as penetrated by mind, both when it is taken as intelligible and, still more interestingly, when poets ascribe to it moods or treat it as kindly or hostile. There is analytic work to be done here to which critical philosophers have still to address themselves.

The organizing principles of nature
      Connected with the questions just discussed are problems about the organizing principles of nature; i.e., about natural causality. It has been said that the Greeks thought of the world as a vast animal (indeed, the conceptual scheme that Aristotle devised for dealing with nature makes sense only if something like this is presupposed). Nature is the sphere in which different kinds of things are all striving to realize their characteristic form; purpose (teleology), though not perhaps explicit purpose, governs it throughout. Aristotle was not entirely insensitive to what are now known as the physical and chemical aspects of the universe, but he treated them as subordinate to the biological aspect (biology) in a way modern thinkers find surprising. Even the four elements—earth, air, fire, and water—were seen by him as each seeking its natural place in the cosmos. The contrast between this view and that favoured by Descartes could hardly be sharper. According to Descartes nature is not an organism but a mechanism; everything in it, including animal and human bodies, although not including the human mind, must be understood on mechanical principles. In taking this line, Descartes was endorsing a way of thinking that was central in the new physical science developed by Galileo at the beginning of the 17th century and that was to remain central in the thought of Newton. Descartes himself was not a pure mechanist because he believed that mind was governed by principles of its own; his work, however, undoubtedly encouraged the thought, frequently debated at the time of the Enlightenment, that mental life equally with the physical world must be explicable in mechanical terms. This was a position whose validity at the theoretical level Kant reluctantly admitted, only to try to turn its edge by his dichotomy of theory and practice. Everything in nature, including human behaviour, was subject to causal determination. The dignity and uniqueness of man, however, could be preserved because of the fact that in moral action man raised himself above the sphere of nature by thinking of himself as part of a world of free spirits.

      Kant also produced interesting thoughts on the subject of living phenomena (life). Reflection on the concept of an organism had convinced him that a being of this sort could never be accounted for satisfactorily in mechanical terms; it was futile to hope that someday in the future there would appear a Newton of biology capable of explaining mechanically the generation of even so apparently simple a thing as a blade of grass. To judge or speak of organic phenomena demanded a special principle that was teleological (i.e., related to design or purpose) rather than mechanical. Kant, however, refused to allow that this principle had constitutive force. It belonged, he said, only to “reflective judgment” and thus did not rank alongside the principles of understanding that were so important in physical science. Men must have recourse to a principle of purposiveness in order to speak of living things, but they must not imagine that such recourse would enable them to explain their existence and behaviour in any strict sense of the term. They have insight only into what they can produce, and what they can produce are machines, not organisms. Many of Kant's detailed remarks on this subject seem outmoded in the light of subsequent scientific developments; nevertheless, the problem he raised is still the subject of vigorous debate among philosophically minded biologists. His emphasis on the uniqueness of the concept of an organism, which he says is only imperfectly explicated in the language of ends and purposes, is particularly valuable.

      It remains to mention the seemingly eccentric view of nature taken by Hegel, who regarded it as at once the antithesis to and a prefiguration of the world of spirit. Nature had to exist to provide material for spirit to overcome, although it was a gross mistake to think of it as essentially a lifeless mechanism. Instead of reducing the organic to the inorganic, men should see the latter as pointing forward to the former, which in turn offered a foretaste of the rational structure exhibited by the world of mind. Hegel's disdain for scientists of proved ability, such as Newton and John Dalton, and his endorsement against them of amateur scientists such as the German writer Goethe, make it hard to take his philosophy of nature seriously. It contains, even so, some interesting points, not least the demonstration that in finding nature to be throughout subject to law the scientist is presupposing that it is thoroughly penetrated by mind. To understand these views properly, however, it is necessary to understand Hegel's system as a whole.

space and time
      Many metaphysicians have argued that neither time nor space can be ultimately real. Temporal and spatial predicates apply only to appearances; reality, or what is real, does not endure through time, nor is it subject to the conditions of space. The roots of this view are to be found in Plato and beyond him in the thought of the Eleatic philosophers Parmenides and Zeno, the propounder of several paradoxes about motion. Plato conceived his Forms as eternal objects whose true location was nowhere. Similarly, Christian philosophers (Christianity) conceived of God as existing from everlasting to everlasting and as present in all parts of the universe. God was not so much in space and time as the source of space and time. Whatever falls within space and time is thereby limited, for one space excludes another and no two times can be simultaneous. God, however, is by definition an infinite being and so must exist timelessly and apart from space.

      Reference has already been made to the way in which Kant argued for an intimate connection between time and space and human sensibility: that human beings experience things as being temporally and spatially situated is to be connected with the nature of their minds, and particularly with their sensory equipment. Kant was entirely correct to describe space and time as “intuitions,” by which he meant that they are peculiar sorts of particulars; he was right again to insist on the centrality in sensing of the notions of here and now, which can be indicated but not reduced to conceptual terms. It is highly doubtful, however, whether he had sufficient grounds for claiming a priori insight into the nature of space and still more that of time; his case for thinking that space and time are “pure” intuitions was palpably inadequate. The lesson to draw from his careful discussion of this subject might well be not that there must be a form of reality lying beyond space and time but rather that nothing can be real that does not conform to spatial and temporal requirements. Space and time are bound up with particularity, and only what is particular can be real.

      It was only in a weak sense that Kant denied the reality of time and space. Other philosophers have certainly been bolder, though generally on the basis of a less solid grasp than Kant possessed of what it is to experience temporally and spatially. Thus, Bradley argued against the view that space and time are “principles of individuation” by alleging that no specification of spatial or temporal position, whether in terms of here and now or by the use of spatial coordinates or dating systems, could achieve uniqueness. Any descriptions such as “at 12 o'clock precisely on January 4, 1962” or “just 75 yards due north of this spot” might apply to infinitely many times or places in the universe, for there was nothing to prevent there being infinitely many temporal and spatial orders. Bradley forgot that the whole meaning of a spatial or temporal description is not exhausted when attention is given to the connotations of the terms used; what has to be considered is the words as used in their context, which is that of a person who can indicate his position in space and time because of the fact that he is himself situated in space and time. One cannot express uniqueness in words as such, but he can use words to express uniqueness. Bradley's (Bradley, F H) suggestion that it is possible to conceive of many temporal and spatial orders is by no means free from controversy. In general, men think of all events as happening before, simultaneously with, or after the moment that is called “now,” all spatial positions as relating in some way or other to the point that is called “here.” In circumstances where this cannot be done, as with events or places in a dream, men dismiss them as quite unreal. That there might be events or places with no relation to their own now and here is something they often refuse to take seriously, though there are theories in modern science that suggest that they are wrong to do so.

      It was pointed out earlier that to say that something is unreal in a metaphysical context is often to say that it is unintelligible, and it is not surprising to find that arguments about the unreality of space and time have often turned on conceptual considerations. Thus, it is alleged that there is an incoherency in the notion of space because it claims to be a whole that is logically prior to its parts, and nevertheless turns out in practice to be merely an indefinitely extensible aggregate. Everything that occupies space falls within a wider spatial context; the thought of space as such is, as Kant saw, involved in any spatial description. Yet space as such is something that constantly eludes man's grasp; space, as man knows it, is just one spatial situation after another.

 The difficulties found in the notion of time turn on the combination in it of the idea that time is continuous and the idea that it is made up of discrete parts. Henri Bergson (Bergson, Henri), a French philosopher who was concerned with the notions of duration and movement, said that time was experienced as continuous; it was only the “spatialized” time measured by clocks that was taken to have separable parts (minutes, hours, weeks, and so on), and this “public” time was merely conventional. This, however, seems altogether too easy a solution of the problem, for privately experienced time also goes by (one stretch of it follows another), and the thesis that public time is merely conventional is at best highly controversial. It must be allowed that time is commonly thought of as at once flowing and, as it were, subject to arrest. Whether this is, in fact, openly inconsistent may be doubted, but it is on points like this that the metaphysical case in question rests.

      Few British or American philosophers discuss these questions now, largely because they have been persuaded by Moore that any attack on such central notions in men's thought as these must be mistaken in principle. As a result, little attention is given to a question that deserves investigation; namely, what is to take the place of space and time in metaphysical thought. Idealist writers (Idealism) constantly said that space and time qualified appearances, and that nothing that did so could fail to be taken up in the higher experience that was experience of reality. But how is this supposed to be done? Time is perhaps cancelled and yet preserved in the idea of eternity, space in the thought of something that is at once omnipresent yet not in any particular place. But what is there that is positive about these notions? The eternal, it is sometimes said, is not to be identified with what lasts through all time; it is, strictly, outside time altogether. But what does it mean to say this? When it is said, for example, that numbers or truths are eternal, the proper inference is that they have nothing to do with time; to inquire when they came into or will go out of existence is to ask a question that is ill posed. When God, however, is said to be eternal, the impression is often given that he has temporal characteristics, although in some higher form. What this higher form is deserves careful consideration, the result of which might be that it is not the conception of time that is incoherent but the conception of God.

The conception of spirit (spiritualism)
      As well as arguing for the separate existence of mental substance, metaphysicians have claimed that mind is, as it were, the key to the understanding of the universe. What exists is spirit, or at least is penetrated by spirit. This is the thesis of Idealism, a type of philosophy that is often derided but that, like its rival Materialism, has a constantly fresh appeal. This view is worth examining in more detail than has so far been possible.

      It is best to begin by distinguishing the thesis of Idealism proper from some others with which it is readily confused. Leibniz (Leibniz, Gottfried Wilhelm) said that the true atoms of nature were monads or souls; at bottom nothing existed except minds. Berkeley claimed that sensible things have no existence without the mind; there are spirits that experience, including an infinite spirit, and there are the contents of their experiences, but there is no independently existing world of matter. For the philosophers who followed Hegel, both Leibniz and Berkeley were “subjective” Idealists (subjective idealism): they conceived of reality in terms of the experiences of individual minds. Hegel's view, by contrast, was that what exists is not so much pure mind as mind writ large; i.e., the universe is penetrated by mind and exists for the sake of mind, and it cannot be understood unless this fact is grasped. Hegel was thus not committed to denying that there is an independent world of nature but, on the contrary, openly proclaimed it. Nature was there for mind to master it and in so doing to discover itself.

 The field in which Hegel first worked out this theory was that of human affairs. The human world may be said to be mind made objective because it consists of a series of structures—examples would be a language, a set of moral or political procedures, a science, a practical art such as medicine—that constitute mental achievements. The mind involved in structures of this kind, however, is collective rather than personal. An art such as medicine or a science such as mathematics is not the invention of any particular individual; and although individuals have contributed and are contributing to the advancement of each structure, they do so not in their personal capacity but as embodying impersonal intelligence.

      Because the human world thus embodies mind, or spirit, it needs to be understood in a special way—in terms of what Hegel called “concrete universals.” (concrete) Concepts of this kind are in order when it is a question of grasping a particular sort of subject matter—one in which there are intimate connections between the data under consideration. Connections in nature are, on the surface at any rate, of a purely external character; striking a match, for example, has nothing internally to do with producing a flame. When, however, a historian considers the different stages of some movement or process, or when an anthropologist studies the various aspects of the life of a society, the material they confront is internally related just because it represents the work of mind—not, of course, of mind working in a vacuum but of mind facing and reacting with greater or less intelligence to particular situations. It is not surprising in these circumstances to find that the conceptual structure employed by the student of human affairs is, in important respects, profoundly different from that employed by the student of nature. In the latter, what are in question are constant conjunctions, observed but not understood; in the former, men have insight into what happens or obtains because they can reenact in their own minds the thought behind the material they study.

      All this is, or should be, comparatively uncontroversial; it represents the truth behind the claim of Wilhelm Dilthey (Dilthey, Wilhelm), a German philosopher and historian of ideas, that human affairs can be understood, as it were, from within, by means of what he called Verstehen (“understanding”). But of course it is one thing to say this and another altogether to argue that the universe at large should be construed as if it were mind writ large. What makes Hegelianism intriguing to some and totally implausible to others is precisely that it makes this extravagant claim. As has already been mentioned, the world of nature for Hegel is in one way independent of mind: its being is certainly not its being perceived. It is, nevertheless, relevant to mind in all sorts of important ways: in providing a setting in which mind can act, in constituting an obstacle that mind can overcome, in presenting mind with something seemingly alien in which it can nevertheless find itself insofar as it discovers nature to be intelligible. If Hegel were asked why there was a world of nature at all, his answer would be “for the sake of mind.” Just as man's social environment affords opportunities to the individual to come to full knowledge of himself by realizing his differences from and dependence upon others, so the world of nature affords similar opportunities. By transforming the natural scene, men make it their own. In so doing they come to know what they can do, and thus what they are.

      There is, perhaps, more to this doctrine than appears at first sight. It is, however, easier to assent to it in general terms than to follow Hegel over it in detail. According to the Idealist account, there is in the end only one true description of the universe, namely that which is couched in terms of the concrete universal. Reality is a single self-differentiating system, all the parts of which are intimately connected; it is spirit that expresses itself in the natural and human worlds and comes to consciousness of itself in so doing. Any other account of the matter—for example, that given by the scientist in terms of experienced uniformities—must be dismissed as inadequate. To Hume's (Hume, David) objection that there is an absolute logical difference between propositions expressing matters of fact and existence and propositions expressing relations of ideas, Hegel replies brusquely that the distinction is untenable. At a certain level, perhaps, facts are taken as “brute.” Even the scientist, however, never abandons his aspiration to understand them—it is only provisionally that he talks in terms of “ultimate inexplicabilities”—and the philosopher knows that the demand to incorporate all knowledge in a single system is not to be denied. It is a demand that, as Hegelians are willing to admit, can in practice never be met but that, nonetheless, ceaselessly makes itself felt. That such is the case is shown by the extraordinary fascination exercised by this strange but remarkable type of philosophy.

      To try to understand the universe in terms of spirit is characteristic of philosophers whose main extra-philosophical interests are in the humanities, particularly in historical studies. Relatively few scientifically minded thinkers have followed this line of thought, and many Idealists of repute, including Bradley and Benedetto Croce (Croce, Benedetto) (an Italian philosopher and literary critic whose major philosophical work was published in four volumes between 1902 and 1917 under the general title La filosofia dello spirito (“The Philosophy of the Spirit”), have been least convincing when writing about science. Hegel himself, perhaps, had less sympathy with scientific than with historical aspirations; this is not to say, however, that he was ill-informed about contemporary science. He knew what was going on, but he saw it all from his own point of view, the point of view of one who was entirely convinced that science could not produce any ultimate answers. He valued science but rejected the scientific view of the world.

Types of metaphysical theory
      To complement and, in a way, to correct this brief survey of the problems of metaphysics it will be useful at this point to insert a short summary of a number of overall metaphysical positions. Metaphysics, as already noted, professes to deal with “the world as a whole”; the thoughts of a metaphysician, if they are to make any impact at all, must be connected in a system. The object in what follows will be to present in outline metaphysical systems that have exercised and, indeed, continue to exercise a strong intellectual appeal. In all cases but one, these systems were given classical shape by particular philosophers of genius. Relatively little attention, however, will be paid to this fact here because the present concern is with types of view rather than with views actually held. Thus, reference will be made to Platonism instead of to the philosophy of Plato, and so on in other cases.

      The essence of Platonism lies in a distinction between two worlds, the familiar world of everyday life, which is the object of the senses, and an unseen world of true realities, which can be the object of the intellect. The ordinary man recognizes the existence of the former and ignores that of the latter; he fails to appreciate the extent to which his beliefs both about fact and about values are arbitrarily assumed and involve internal contradictions. The philosopher is in a position to show him how insubstantial is the foundation on which he takes his stand. The philosopher can demonstrate how little thought there is in popular conceptions of good and evil, and he can show that the very concept of sense knowledge involves difficulties because knowledge presupposes a stable object, and the objects of sense are constantly changing. The claim, however, is that he can do more than this. Because of the presence in him of something like a divine spark, he can, after suitable preparation, fix his intellectual gaze on the realities of the unseen world and, in the light of them, know both what is true and how to behave. He will not attain this result easily—to get to it will involve not only immense intellectual effort, including the repeated challenging of assumptions, but also turning his back on everything in life that is merely sensual or animal. Yet, despite this, the end is attainable in principle, and the man who arrives at it will exercise the most important part of himself in the best way that is open to him.

      That this type of view has an immediate appeal to persons of a certain kind goes without saying. There is ample evidence in poetry and elsewhere of the frequently experienced sense of the unreality of familiar things and the presence behind them of another order altogether. Platonism may be said to build on “intuitions” of this kind; as a metaphysics, its job is to give them intellectual expression, to transfer them from the level of sentiment to that of theory. It is important, however, to notice that Platonism is not just the intellectualizing of a mood; it is an attempt to solve specific problems in a specific way. In Plato's own case, the problems were set by loss of confidence in traditional morality and the emergence of the doctrine that “man is the measure of all things.” Plato thought he could counter this doctrine by appeal to another contemporary fact, the rise of science as shown in the development of mathematical knowledge (mathematics, philosophy of). Mathematics, as he saw it, offered certain truth, although not about the familiar world; the triangle whose properties were investigated by the geometrician was not any particular triangle but the prototype that all particular triangles presuppose. The triangle and the circle belonged not to the world of the senses but to the world of the intelligence; they were Forms. If this could be said of the objects of mathematical discourse, the same should also be true of the objects of morality. True justice and true goodness were not to be found in popular opinions or human institutions but should be seen as unchanging Forms, eternally existing in a world apart.

      Modern philosophers have found much to criticize in this system: as indicated already, they have objected that Forms are not so much existents as abstractions, and they have found the argument from science to morality quite inconclusive because of what they allege to be an absolute dichotomy between fact and value. It may be that nobody today can subscribe to Platonism in precisely the form given it by Plato himself. The general idea, however, has certainly not lost its hold, nor have the moral perplexities to which Plato hoped to find an answer been dissipated by further thought.

      For many people, Plato is the type of an other-worldly, Aristotle of a this-worldly philosopher. Plato found reality to lie in things wholly remote from sense; Aristotle took form to be typically embodied in matter and thought it his job as a philosopher to make sense of the here and now. The contrast is to some extent overdrawn for Aristotle, too, believed in pure form (God and the astral intelligences—the intelligent movers of the planets—were supposed to satisfy this description), and Plato was sufficiently concerned with the here and now to want to change human society radically. It remains true, nevertheless, that Aristotelianism is in essentials a form of immanent metaphysics, a theory that instructs men on how to take the world they know rather than one that gives them news of an altogether different world.

      The key concepts in Aristotelianism are substance, form and matter (form), potentiality and actuality, and cause. Whatever happens involves some substance or substances; unless there were substances, in the sense of concrete existents, nothing could be real whatsoever. Substances, however, are not, as the name might suggest, mere parcels of matter; they are intelligible structures, or forms, embodied in matter. That a thing is of a certain kind means that it has a certain form or structure. But the structure as conceived in Aristotelianism is not merely static. Every substance, in this view, not only has a form but is, as it were, striving to attain its natural form; it is seeking to be in actuality what it is potentially, which is in effect to be a proper specimen of its kind. Because this is so, explanation in this system must be given in teleological rather than mechanical terms. For Aristotle, form is the determining element in the universe, but it operates by drawing things on, so that they become what they have it in themselves to be rather than by acting as a constant efficient cause (i.e., the agent that initiates the process of change). The notion of an efficient cause has a role in Aristotelianism—as Aristotle put it, it takes a man, a developed specimen of his kind, to beget a man; it is, however, a subordinate role and yields pride of place to a different idea, namely, form considered as purpose.

      For reasons connected with his astronomy, Aristotle postulated a God. His God, however, had nothing to do with the universe; it was not his creation, and he was, of necessity, indifferent to its vicissitudes (he could not otherwise have been an unmoved mover). It is a mistake to imagine that everything in the Aristotelian universe is trying to fulfill a purpose that God has ordained for it. On the contrary, the teleology of which use is here made is unconscious; although things all tend to an end, they do not in general consciously seek that end. They are like organs in a living body that fulfill a function and yet seemingly have not been put there for that purpose.

      As this last remark will suggest, an important source of Aristotelian thought is reflection on natural growth and decay. Aristotle, who was the son of a doctor, was himself a pioneer in natural history, and it is not surprising that he thought in biological terms. What is surprising, and gives his system a continuing interest, is the extent to which he succeeded in applying ideas in fields that are remote from their origin. He was without doubt more successful in some fields than in others: in dealing with the phenomena of social life, for instance, as opposed to those of physical reality. His results overall, however, were impressive enough for his system not only to dominate men's minds for many centuries but to constitute a challenge even today. Men still, on occasions, think like Aristotle, and, as long as that is so, Aristotelianism will remain a live metaphysical option.

 The advent of Christianity had important effects in philosophy as in other aspects of human life. Initially Christians were opposed to philosophical claims of any kind; they saw philosophy as an essentially pagan phenomenon and refused to allow the propriety of subjecting Christian dogma to philosophical scrutiny. Christian truth rested on revelation and did not need any certificate of authenticity from mere reason. Later, however, attempts were made to produce a specifically Christian metaphysics, to think out a view of the universe and of man's place in it that did justice to the Christian revelation and nevertheless rested on arguments that might be expected to convince Christians and non-Christians alike. St. Thomas Aquinas was only one of a number of important thinkers in medieval times who produced Christian philosophies; others—such as the philosophers John Duns Scotus in the late 13th century and William of Ockham in the first half of the 14th century—took significantly different views. In selecting the system of Aquinas for summary here, the factor that has weighed most has been its persistent influence, particularly in postmedieval times. Aquinas was not the only medieval philosopher of distinction, but Thomism is alive as other medieval systems are not.

      The central claim of Thomism is that reflection on everyday things and the everyday world reveals it as pointing beyond itself to God as its sustaining cause. Ordinary existents, such as human beings, are in process of constant change. The change, however, is not normally the result of their own efforts, and even when it is, it does not depend on them exclusively. No object in the familiar world can fully account for its own esse (i.e., its own act of existing), nor is it wholly self-sufficient; all are affected from without, or at least operate in an environment that is not of their own making. To say this is to say that they are one and all finite. Although finite things can be, and commonly are, stimulated to activity or kept in activity by other finite things, it does not follow that there might be finite things and nothing else. On the contrary, the finite necessarily points beyond itself to the infinite; the system of limited beings, each dependent for its activity on something else of the same kind, demands for its completion the existence of an unlimited being, one that is the source of change in other things but is not subject to change itself. Such a being would be not a cause like any other but a first or ultimate cause; it would be the unconditioned condition of the existence of all other things. Aquinas believed that human reason can produce definitive proofs of the existence of an infinite or perfect being, and he had no hesitation in identifying that being with the Christian God. Because, however, the movement of his thought was from finite to infinite, he claimed to possess only so much philosophical knowledge of the Creator as could be arrived at from study of his creation. Positive knowledge of the divine nature was not available; apart from revelation, man could only say what God is not, or conceive of his attributes by the imperfect method of analogy.

      Aquinas worked out his ideas at a time when the philosophy of Aristotle was again becoming familiar in western Europe after a period of being largely forgotten, and many of his detailed theories show Aristotelian influence. He assumed the general truth of the Aristotelian picture of the natural world and the general correctness of Aristotle's way of interpreting natural phenomena. He also took over many of Aristotle's ideas in the fields of ethics and politics. He gave the latter, however, a distinctively different twist by making the final end of man not philosophical contemplation but the attainment of the beatific vision of God; it was Christian rather than Greek ideas that finally shaped his view of the summum bonum (“greatest good”). Similarly, his celebrated proofs of God's existence proceeded against a background that is obviously Aristotelian but that need not be presupposed for their central thought to have validity. Thomism can certainly be seen, and historically must be seen, as the system of Aristotle adapted to Christian purposes. It is important, however, to stress that the adaptation resulted in something new, a distinctive way of looking at the world that still has its adherents and still commands the respect of philosophers.

      René Descartes worked out his metaphysics at a time of rapid advance in human understanding of the physical world. He adopted from Galileo the view that physical things are not what they are commonly taken to be on the strength of sense experience—namely, possessors of “secondary” properties such as colour, smell, and feel—but are rather objects characterized only by the “primary” qualities of shape, size, mass, and mobility. To understand why a constituent of the physical world behaves as it does, what should be asked is where it is, how large it is, in what direction it is moving, and at what speed; once these questions are answered, its further properties will become intelligible. Descartes held further that all change and movement in the physical world is to be explained in purely mechanical terms. God was needed to give initial impetus to the physical system as a whole, but once it had got going it proceeded of its own accord. To pretend, as the Aristotelians had, to discern purposes in nature was to make the impious claim to insight into God's mind. Descartes applied this theory to the movements of animals as much as to those of inanimate bodies; he thought of both as mere automatons, pushed and pulled about by forces over which they had no control.

      Although Descartes thus acquiesced in, indeed emphasized, the mechanistic tendencies of contemporary science, he was far from being a Materialist. Besides material substance there was also thinking substance (mind), and this was in fact wholly different from matter both in kind and in operation. Bodies had as their essence to occupy space; minds were not in space at all. Bodies, again, were determined in their movements; minds were in some sense free, because they possessed will as well as intelligence. Descartes was less explicit on this point than he might have been; the principles on which mental substance is supposed to operate are not made clear, with the result that critics have said that Descartes thought of mental activities in para-mechanical terms. Whether this is true or not, however, there was no reason for Descartes to be in any special difficulty over this point. All he needed to urge was that minds act in the strict sense of the term, which is to say that they take cognizance of their situation and respond more or less intelligently to it. That they can do this differentiates them fundamentally from material things, which are caused to do what they do and are entirely unaffected by rational considerations.

      The main crux in Descartes's metaphysics was the difficulty of bringing together the two orders of being, once they were separated. Mention has already been made of the expedient to which later Cartesians were driven in trying to solve this difficulty: in effect, they made the unity of the universe a continuing miracle, dependent upon the grace of God. It is worth mentioning here another move in the same area that many have found instructive. Kant, who was in some respects both a latterday Cartesian and a latter-day Platonist, argued that human activities could be looked at from two points of view. From the theoretical standpoint they were simply a set of happenings, brought about by antecedent events in precisely the same way as occurrences in the natural world. From the standpoint of the agent, however, they must be conceived as the product of rational decision, as acts proper for which the agent could be held responsible. The moment he began to act, a man transferred himself in thought from the phenomenal world of science to an intelligible world of pure spirit; he necessarily acted as if he were not determined by natural forces. The transference, however, was a transference in thought only (to claim any knowledge of the intelligible world was quite unjustified), and because of this the problem of the unity of the universe was dissolved. There was no contradiction in a man's thinking of himself both as a subject for science and as a free originator of action. Contradiction would appear only if he were present in both respects in an identical capacity. But appeal to the doctrine of the two standpoints was thought by Kant to rule this out.

      It is only with some hesitation that one can speak of Kant as having put forward a metaphysics. He was in general highly suspicious of claims to metaphysical knowledge, and a principal aim of his philosophy was to expose the confusions into which professing metaphysicians had fallen. Nevertheless, it is clear that Kant had metaphysical convictions, for all his denial of the possibility of metaphysical knowledge; he was committed to the view that men can conceive a non-natural as well as a natural order and must necessarily take the former to be real when they act. The language he used—particularly his talk about man as phenomenon and man as noumenon—is not to the taste of present-day philosophers, but the thought behind it certainly survives. It is in this form, indeed, that Cartesianism may still be said to present a serious intellectual challenge.

      Descartes and Kant were both adherents of metaphysical dualism, though they worked out their dualisms in interestingly different ways. Many thinkers, however, find dualism unsatisfactory in itself; they look for a single principle by which to compass whatever exists. There are two broad steps that are open to the person who confronts a dualism of mind and matter and finds it unsatisfactory: he can either try to show that matter is in some sense reducible to mind, or conversely seek to reduce mind to matter. The first is the solution of Idealism, the second that of Materialism. Idealism has already been treated at length, and it will not be necessary to go into it again here. Only one point about it needs emphasis. As was pointed out, there are various forms of Idealism. In one version, this philosophy maintains that there literally is no such thing as matter; what the common man takes to be material things are, upon closer consideration, nothing but experiences in minds. Nothing exists but minds and their contents; an independently existing material world is strictly no more than an illusion. This was the view taken by Berkeley. In the more sophisticated Idealism of Hegel, however, it is not maintained that mind alone exists; material things are, in one way, taken to be as real as minds. The thesis advanced is rather that the universe must be seen as penetrated by mind, indeed as constituted by it. Spirit, to use Hegel's own word, is the fundamental reality, and everything that exists must accordingly be understood by reference to it, either as being directly explicable in spiritual terms or as prefiguring or pointing forward to spirit. Whatever the merits of this thesis, it is clear that it differs radically from that maintained by Berkeley. Idealism in the form espoused by Berkeley (Berkeley, George) relies largely on arguments drawn from epistemology, though formally its conclusions are ontological, because they take the form of assertions or denials of existence. Hegel, however, had little or nothing to say about epistemology and was not even concerned to put forward an ontology. What he wanted to urge was a doctrine of first principles, a thesis about the terms in which to understand the world. The Hegelian (Hegel, Georg Wilhelm Friedrich) “reduction” of matter to mind was thus reduction in a somewhat attenuated sense. It is important to get this point clear, if only because it has its parallel in the rival doctrine of Materialism.

      The simplest form of Materialism is found in the claim that only matter exists. Stated thus baldly the claim is absurd, because it is clear that all sorts of things exist that are not of the nature of matter: thoughts and numbers and human institutions would be instances. In the light of these facts, the claim has to be revised to say that matter is the only substantial existent, with appeal being made to distinctions first worked out in Aristotle's doctrine of categories. According to this explanation, many things besides matter exist, but all of them are explicable (or so it is said) as modifications of matter. Thus, human institutions consist in patterns of movement among specific groups of human beings, and human beings in turn are nothing but highly complicated material bodies.

      It is clear from these instances that Materialism is a controversial doctrine; it is also clear that its key word, modification, requires further explanation. When, for example, minds (mind) are said to be modifications of an underlying material substance, what is meant? A first and relatively easy point is that, like qualities and quantities, they could not exist separately. Unless there were material bodies, there could not be minds, because minds are—to put it crudely—states found in some material bodies. Minds are here equated with mentality, and mentality is clearly an abstraction. To say this, however, is not to remove the whole difficulty. When it is said that mentality is a state of some material body or bodies, is that meant literally or metaphorically? Bodies can often be described from the physical point of view as being in a certain state—for example, as being in a state of internal equilibrium. What is meant here is that the different particles of matter concerned stand in a certain relationship and as a consequence develop certain physical properties. But is mentality to be conceived as a physical property? It sounds extravagant to say so. Yet some such doctrine must be defended if Materialism is to be advanced as a form of ontology with a serious claim for attention. It is interesting in this connection to notice the arguments advanced by scholars like J.J.C. Smart, which purport to identify states of mind with states of the brain. If the two are identical—literally the same thing described from two points of view—thoughts may really be modifications of matter, and Materialism may be tenable in a strong form. If, however, the identity cannot be made out—and very few philosophers are in fact ready to accept it—Materialism can be true at most in a modified form.

      This modified form of Materialism is perhaps better described as naturalism. Naturalism holds not that all things consist of matter or its modifications but that whatever exists can be satisfactorily explained in natural terms. To explain something in natural terms is to explain it on scientific lines (science, philosophy of); naturalism is in fact a proclamation of the omnicompetence, or final competence, of science. It is not essential to this type of view to argue that phenomena can be spoken of in one way only; on this point, as on the point about ontological reducibility, the theory can afford to be liberal. It is, however, vital to make out that the scientific account of a set of happenings takes precedence over any other. Thus, the language in which men commonly speak of action and decision, which may be called for short the language of reasons, must be held to be secondary to the language in which scientists might speak of the same facts. Scientific language is basically causal, and the thesis of this form of Materialism is that causal explanations are fundamental. Naturalism is thus the obverse of Hegelianism; it is a theory of first principles, and it draws its principles from science.

      If the question is raised why anyone should take this form of Materialism seriously, the answer lies in a number of significant facts. Physiologists have established correlations between general states of mind and general states of brain activity; their hope is to extend this to the point where particular thoughts and feelings can be shown to have their physiological counterpart. Cyberneticists have produced artifacts that exhibit mindlike behaviour to a remarkable degree; the inference that man is no more than a complicated machine is certainly strengthened by their achievements. Sociologists have shown that, whatever the explicit reasons men give for their beliefs, these are often intelligible in the light of factors of which they themselves take little or no account. The old assumption that human judgments are typically grounded in reason rather than merely caused, is called in question by the results of such investigations, which gain support from findings both in Freudian and in orthodox psychology. None of this evidence is decisive by itself; there are ways in every case of blocking the conclusions that Materialists tend to draw from it. Yet it remains true that, cumulatively, the evidence is impressive. It certainly has enough force to make it necessary to take this type of theory with the greatest seriousness. Metaphysical disputes in the modern world are fundamentally arguments for or against Materialism, and the other types of theory here explored are all seen as alternatives to this compelling, if often unwelcome, view.

Argument, assertion, and method in metaphysics
      Attention is now turned from description of the content of particular metaphysical views to more general treatment of the nature of metaphysical claims. The questions that will arise in this section concern such things as the nature and basis of metaphysical assertions, the character of metaphysical arguments and of what are taken to be metaphysical proofs, and the parts played in metaphysical thinking by insight and argument, respectively. They come together in the inquiry as to whether metaphysics can be said to be a science and, if so, what sort of a science it is.

Metaphysics as a science
Nature of an a priori science
      Sciences are broadly of two kinds, a priori (a priori knowledge) and empirical. In an a priori science such as geometry, a start is made from propositions that are generally taken to be true, and the procedure is to demonstrate with rigorous logic (applied logic) what follows if they are indeed true. It is not necessary that the primary premises of an a priori science should in fact be truths; for the purposes of the system they need only be taken as true, or postulated as such. The main interest is not so much in the premises as in their consequences, which the investigator has to set out in due order. The primary premises must, of course, be consistent one with another, and they may be chosen, as in fact happened with Euclidean geometry, because they are thought to have evident application in the real world. This second condition, however, need not be fulfilled; a science of this kind can be and commonly is entirely hypothetical. Its force consists in the demonstration that commitment to the premises necessitates commitment to the conclusions: the first cannot be true if the second are false.

      This point about the hypothetical character of a priori sciences has not always been appreciated. In many classical discussions of the subject, the assumption was made that a system of this kind will start from as well as terminate in truths and that necessity will attach to premises and conclusions alike. Aristotle and Descartes both spoke as if this must be the case. It is clear, however, that in this they were mistaken. The form of a typical argument in this field is as follows: (1) p is taken as true or given as true; (2) it is seen that if p, then q; (3) q is deduced as true, given the truth of p. There is no need here for p to be a necessary or self-guaranteeing truth; p can be any proposition whatsoever, provided its truth is granted. The only necessity that needs to be present is that which characterizes the argument form, “If p is true, and p implies q, then q is true,” that is [p · (pq)] ⊃ q, in which · symbolizes “and,” and ⊃ means “implies”; and this is a formula that belongs to logic. It is this fact that makes philosophers say, misleadingly, that a priori sciences are one and all analytic (analytic proposition). They are not because their premises need not answer this description. They, nevertheless, draw their lifeblood from analytic principles.

Metaphysics as an a priori science
 It is clear that metaphysical philosophers have sometimes aspired to present their results in the form of a deductive system, to make metaphysics an a priori science. For this purpose they have taken a deductive system to require not just that the premises entail the conclusions but further that they themselves be necessarily true. Spinoza (Spinoza, Benedict de) thus began the first book of his Ethics by laying down eight definitions and seven axioms whose truth he took to be self-evident and then proceeding in the body of the text to deduce, as he thought with strict logic, 36 propositions that follow in order from them. He repeated the procedure in the rest of his work. That philosophical conclusions should thus be capable of being set out “in the geometrical manner” was something that Spinoza took as axiomatic; to be worthy of attention at all, philosophy must issue in knowledge as opposed to mere opinion, and knowledge proper had to be exempt from the possibility of doubt, which meant that it must either be intuitively evident or deducible from what was intuitively evident. Spinoza took this conception of knowledge from Descartes, who had himself toyed with the idea of presenting metaphysical arguments in the geometrical manner. Descartes, however, pointed out that, although there was no difficulty in getting agreement to the first principles of geometry, “nothing in metaphysics causes more trouble than the making the perception of its primary notions clear and distinct”; the whole trouble with this discipline is that its students fail to see that they must start from what are in fact the basic truths. Descartes himself spoke as if the problem were no more than pedagogical; it was a question of making people see as self-evident what is in itself self-evident. His own “analytic” approach in the Meditationes was chosen to overcome these difficulties; it was, he said, “the best and truest method of teaching.” But it may well be that this account is too optimistic. The difficulty with a system such as those of Descartes and Spinoza is that there are persons who cannot be brought to see that the primary propositions of the system are self-evidently true, and this not because they are lacking in attention or insight but because they see the world in a different way. This suggests that in any such system there will necessarily be an element that is arbitrary, or at least noncompulsive. However cogent the links that bind premises to conclusions, the premises themselves will lack a firm foundation. If they do, the interest of the system as a whole must be greatly diminished; it can be admired as an exercise in logic but not valued for more than that.

      To avoid this unpalatable conclusion, two expedients are possible. The first is to say that the first premises of a metaphysical system must be not merely self-evident but also self-guaranteeing; they must be such that any attempt to deny them can only result in their reaffirmation. Descartes believed that he could satisfy this requirement by grounding his system in the cogito, though strictly this was the primary truth only from the point of view of subjective exposition and not according to the objective order of things. Aristotle somewhat similarly had argued that the logical principle of noncontradiction, which he took to express a highly general truth about the world, must be accepted as axiomatic on the ground that its correctness is presupposed in any argument directed against it.

      Even the Idealists Bradley and Bernard Bosanquet (Bosanquet, Bernard) at times spoke as if the first principles of their system were in some way logically compulsive; as Bosanquet put it, one had either to accept them or recognize that one could know nothing. Whatever the position may be about particular metaphysical propositions, however, it seems clear that not all truths that are taken as basic in metaphysics have the characteristic of being self-guaranteeing. A Materialist takes it as fundamental that whatever occurs happens as a result of the operation of natural causes; a theist sees things in the world as finite and thus as pointing beyond themselves to the infinite being who is their ground. No contradiction is involved in denying these positions, though of course for those who accept them the denial necessarily involves commitment to falsehood. It is, however, one thing for a proposition or set of propositions to be false, another altogether for it to be necessarily false. If the first principles of metaphysics were really self-guaranteeing, only one system of metaphysics could be coherent, and it would be true just because it was coherent. The very fact that there is an apparent choice between competing metaphysical systems, which may differ in plausibility but agree in being each internally self-consistent, rules this possibility out.

      The alternative is to argue that fundamental metaphysical propositions, though not self-guaranteeing, are nevertheless not arbitrary; they have or, to be more cautious, can have a firm foundation in fact. Metaphysical speculation is not, as some opponents of metaphysics have suggested, essentially idle—that is, the mere working out of the logical consequences of premises that the metaphysician chooses to take as true. Or, rather, it does not necessarily answer this description because a metaphysician can have insight into the true nature of things and can ground his system on that. This second position in fact involves arguing that metaphysics is not an a priori but an empirical science.

Metaphysics as an empirical science
      If metaphysics is an empirical science, the question of whether or not to accept a metaphysical theory must be answerable, in part at any rate, by reference to experience. It will not depend on experience alone, any more than does the acceptability of a scientific theory, because here, as in the scientific case, thinking comes into the reckoning too. A metaphysician can be mistaken in his deductions, just as a scientist can. But even if these are impeccable, he will not necessarily succeed on this view of his undertaking. It may be that he argues correctly from premises that are unacceptable—unacceptable because they lack the necessary foundation in fact. He will then be like a scientist who puts forward a hypothesis and deduces its consequences without mistake only to find that experience fails to confirm the supposition on which he is working.

      Scientific hypotheses are refuted, or at least called seriously into question, when predictions based on them fail to come true. As Karl Popper (Popper, Sir Karl)—who has emphasized that there is a unity of method in all generalizing or theoretical sciences—has insisted, every scientific hypothesis must be testable, and the way to test it is to look for circumstances in which it does not hold. To content oneself with favourable evidence is not enough; one must be searching all the time for unfavourable evidence. Further, it must be possible, if the hypothesis is genuinely scientific, to specify in advance what would count as unfavourable evidence; the circumstances in which the hypothesis needs to be abandoned, or at least modified, must be indicated precisely. In ideal conditions it is possible to devise a crucial experiment that will test a hypothesis definitively; the Michelson–Morely experiment, which disposed of the theory of the luminiferous ether, was such an experiment.

      It can be asked, however, what parallels there are to this in metaphysics. The difficulty with testing a metaphysical thesis is twofold. First, metaphysical theories tend to be extremely general and as such highly unspecific. They announce, for example, that every event has some cause or other, or that every change is part of a process that serves some purpose. To find counterexamples to theses of such generality is on any account exceedingly difficult: how can one be sure that all the possibilities have been explored? There is, however, another and still more serious difficulty. The scientist, once he has laid down the conditions that would have to obtain for his hypothesis to prove false, makes no bones about their occurrence; it is, typically, a matter of whether or not a certain pointer reading is registered, and this is a simple question of ascertainable fact. Fact for the metaphysician, however, is altogether more slippery. Different metaphysicians see the world each in his separate way; what they take to be the case is coloured by their metaphysical conceptions. There is no neutral body of facts to which appeal can be made to show that a metaphysical theory falls down, and this being so, the attempt to assimilate metaphysics to science must fail.

      That this should be the case is perhaps not surprising. Scientific thinking proceeds within a framework of presuppositions that it is the business of the scientist to use, not to argue for and still less to challenge—presuppositions to the effect, for example, that every change has a natural explanation. No doubt scientists can change their presuppositions, but they seldom do so consciously; their usual practice is to take them for granted. Metaphysicians, however, necessarily take a very different attitude toward presuppositions. It is their business to tell men how to understand the world, and this means that they must, among other things, put forward and argue for a set of interpretative principles. Metaphysicians differ radically in the interpretative principles they accept, and it is this that explains their failure to agree upon what to take as fact. It is naïve to suppose that the points at issue between, for example, a Thomist and a Materialist can be settled by observation or even by experiment; the facts to which one might appeal in support of his theory may be seen in a very different light by the other, or perhaps be dismissed as simple illusion. Reflection on the phenomenon of religious experience will illustrate what is meant here. That men undergoing this experience are affected mentally and physically in certain specific ways is perhaps common to both Thomist and Materialist. But the further description of their state is entirely controversial and owes its controversial character to the varying preconceptions that the disputants bring to their task.

Initial metaphysical insights
      If metaphysics is far from being a simple empirical discipline, however, it does not follow that it is wholly without foundation in fact. The true situation can perhaps be put as follows. Every metaphysic consists in an imaginative view of the world elaborated into a conceptual system. Metaphysics, like poetry, begins by being a matter of vision; a metaphysician sees the scheme of all things in a certain light; for example, as nothing more than a vast mechanism or as God's creation. As a metaphysician, however, he cannot be content to rest in a vision of this sort, as for example the Romantic poet William Wordsworth does in his “Intimations of Immortality.” He needs to think out terms in which whatever exists can be described so as to accord with his primary insight; he needs to produce and apply a conceptual system and to argue against possible alternatives. Whatever its origins, metaphysics is strictly intellectual in its development. When the question is raised of the source from which metaphysicians gain their initial insights, the answer that occurs most readily is that they are derived from reflection on certain evident facts. Thus, the source of the Materialist view of the world is undoubtedly the practice of science; the Materialist proposes to give unrestricted validity to ways of thinking that scientists have found effective in a certain restricted sphere. The source of Idealist thought is to be found in the practice of history, or more generally in the interpersonal relations of beings who are at once rational and sensitive; the Idealist philosopher takes concepts that are appropriate in these limited areas to apply to the whole of reality. Every system of metaphysics is grounded in some real experience and owes its initial appeal to that fact. This is not to say, however, that the metaphysician builds on experience as does his scientific colleague. To think that is to take altogether too simple a view of the whole question.

Tests of validity
      A question of immense importance is whether there are any means of comparing the validity of initial metaphysical insights. If it has to be answered negatively—if it has to be allowed that, as it were, all candidates in this field start and finish on an equal footing—the argument that each of them has a foundation in fact will be entirely discounted. Whatever respectability their concepts possess in their original homes will be lost once they fall into the hands of the metaphysician, because the procedure of the latter in taking them up and extending them is essentially arbitrary. For example, that one sees the sum of things as a vast machine may be suggested by what goes on in science, but this view can neither claim scientific warrant itself nor draw on scientific prestige, because it seems to spring from nothing better than mere whim. There are, however, two reasons for thinking that initial metaphysical insights are based not on mere whim but on valid grounds.

      First, the number of what may be called viable metaphysical insights is in practice limited: there are varying ways of taking the world as a whole, but not an infinite variety. In the outline account of metaphysical theories given above, six different kinds of view were distinguished, each of which may be said to be grounded in one or more areas of experience. It would be possible to extend the list, but probably not very far; further candidates might well turn out to be no more than variations on themes already considered. Thus, Leibniz might be seen as a latter-day Platonist, and Spinoza as offering a different version of the dualism of Descartes, one that is more sympathetic to Materialism than was Descartes (Descartes, René) himself. If these claims are true, they are certainly important; for the facts here adduced suggest that the experiences or visions on which different metaphysicians build are not peculiar to individual minds but occur commonly and regularly. They are not the product of passing moods, seized on and exploited for no good reason, but connect with thoughts that recur repeatedly in sensitive and intelligent reflection.

      Second, there is a sense in which, despite everything said above, metaphysical theories are subject to the test of experience. That metaphysics aspires to give an account of the world as a whole means that each metaphysician claims that his fundamental insight illuminates every department of life. It may be that there are no neutral facts to which a metaphysician can appeal to show the shortcomings of his opponents; metaphysicians pronounce on what is to count as fact, and this puts them in the happy position of being judges in their own case. It remains true, however, that everyone who engages in that type of philosophy has the formal task of accounting for all the facts that he recognizes, and this is something that can be done more or less well. The value of different metaphysical insights is sometimes shown in the success with which they are applied. Furthermore, it is not quite true that the metaphysician need consult no opinion but his own when it comes to working out his views. What might be called public opinion has a part to play as well, though it has no absolute right to a hearing. A metaphysician who chooses to dismiss areas of experience or ways of thinking that are commonly accepted as being in order does so at his peril; he reduces the initial plausibility of his own theories the oftener he finds himself in this position. He could, of course, be right and common opinion wrong; no genuine metaphysician is put off by the thought of such a conflict. Though he is not put off, however, he has to be wary all the same. He may be able to say what in the end is to count as fact, but if this involves him in dismissing as illusory what instructed opinion generally takes to be real, his triumph may be hollow. Whether he likes it or not, he has to frame a theory that will carry conviction with experts in the different fields concerned, or, if that is going too far, one that will strike them as not wholly implausible. A metaphysician who exercises his veto past that point is simply failing to do his job.

      It must be admitted that the tests one can apply to determine the value of a metaphysical theory are at best unsatisfactory. Often one is driven back onto the expedient of asking if the theory is internally self-consistent; a surprisingly large number of philosophical theories are not. To confute a philosopher out of his own mouth is, perhaps, the most effective form of confutation. If this expedient will not apply, however, the questioner is not quite helpless. Whatever the explanation, it is a well-known fact that a philosopher can purchase consistency at the expense of plausibility; he can put forward theories that evade difficulties by simply declaring them nonexistent. In so doing, he turns his back on what instructed opinion generally takes to be fact. His hope is, of course, to persuade others to see the situation as he does, and there is always the possibility that he will succeed. If, however, after a suitable interval he has not, that must surely count against him. It is by this test that one decides, for example, that the metaphysics of Hobbes is not worth prolonged study, despite the enormous ingenuity of its author; there is too much in this system that seems to be sheerly arbitrary. The same comment could be made of certain forms of Idealism, which are so intent on the omnipresence of spirit that they neglect the materiality of the material order. Admittedly, the test is harder to apply when attention is transferred to the major theories in their most persuasive form, because here the question concerns views that have stood the test of time. It is not, however, entirely inapplicable even there. An individual, at least, may feel that this or that view will not do precisely because it achieves comprehensiveness by turning its back on fact; and, though it is unsatisfactory to fall back on personal judgment in this way, there is perhaps no other alternative in this difficult area.

Role of personal or social factors
      Some writers on the philosophy of philosophy, such as Dilthey, have suggested that the persistence of a plurality of metaphysical systems is to be explained in terms of personal or social factors. Certain kinds of metaphysical outlook appeal to certain types of human being, or gain currency in social circumstances of this kind or that; to understand why they are accepted, recourse must be had to psychology or sociology or both. In the above account, stress has been laid on the historical background against which a number of famous metaphysical theories got their classical formulations; it is idle to deny that each was originally designed to solve a problem deemed to be urgent at the time. Nevertheless, the problem was, of course, an intellectual problem, and the solution offered claimed to be true, not simply comforting. No doubt wishful thinking is as rife in the field of metaphysics as anywhere; it is all too easy here to confuse what men ought to believe with what they want to believe. Philosophies reveal something about their authors and even about their historical age, as works of literature do; they constitute historical evidence as books on mathematics, perhaps, do not. Yet all this can be admitted without agreeing that metaphysics is merely of psychological or historical importance. Science does not cease to be true because it is shown to be useful. Nor is it true that metaphysical theories always in fact give comfort; there are cases in which men find themselves returning over and over again to possibilities that they would very much like to believe were not realized. A philosopher can commit himself to a view of the world that is not at all to his taste, simply because it seems to him on due consideration that this is how things are. That philosophers are godlike beings able to rise entirely above the limitations of their age seems unlikely. It is equally unlikely, however, that their opinions are determined throughout by nonrational factors, and thus that their thinking can lay no claim to truth.

Metaphysical arguments
Logical character of metaphysical statements
      Metaphysical statements fall into two main classes: statements about what exists and prescriptions about how to take or understand what exists. It might seem obvious that the first is the more important; the metaphysician first lays down what he takes to exist, and then tells how to interpret it. This would be correct if metaphysics were a departmental inquiry like, for example, botany; but, of course, it is not. Metaphysicians possess no special resources for the detection of unfamiliar entities, and in consequence the realities they accept must all be argued for. The fundamental items that fill the metaphysical world are one and all theoretical; they are not so much palpable realities as artificial constructs. That being so, there is less of a gulf between the two types of metaphysical pronouncement than might at first appear. It could indeed be argued that the two go closely together to constitute what may be called a metaphysical point of view, a standpoint whose primary purpose is to provide understanding. In a metaphysical context, to say what exists is itself a step on the way to understanding; it is not something that antedates theory, but part of a theory itself.

      It may be asked whether metaphysical pronouncements are empirical or a priori and, if the latter, whether they are analytic or synthetic. They are certainly not straightforwardly empirical, for reasons just set out, and cannot be merely analytic (i.e., true in virtue of the definitions of their terms and of the laws of logic) if metaphysics is to retain any significance. The conclusion that they must be synthetic a priori (i.e., such that, unlike analytic propositions, they convey new knowledge and yet claim complete universality and necessity) seems to follow, and it is just what the opponent of metaphysics wants the metaphysician to adopt. Metaphysics, as he sees it, is a wholly unwarranted attempt to say what the world must be like on the strength of pure thinking, an attempt that is doomed to failure from the start. Before this condemnation is accepted, however, the function that the metaphysician assigns to his principles should be considered. When this is done, it becomes plain that the charge that he claims factual knowledge of a nonempirical sort is false; in one way he recognizes exactly the same facts as anyone else. Where he claims superiority is in knowing how to take facts, and the burden of his message consists in the advocacy of principles that, he alleges, will provide overall understanding. One can describe these principles as synthetic a priori if one chooses. It is probably best, however, to avoid this misleading term and simply say that they are thought of by the metaphysician as applying unequivocally to whatever falls within experience. These metaphysical principles are instructive at least in the sense of having alternatives, and they are certainly treated as being necessary. It is not true, however, that they take the form of statements of fact, even highly general statements of fact; nor is their necessity the same as that which characterizes logical truths. The principles are prescriptions rather than statements, and their necessity arises from the role they play in the constitution of experiential knowledge. It is a necessity that is in one way absolute: nothing that can claim to be real can escape their jurisdiction, because they tell how to take whatever occurs. Nevertheless, in another way the necessity of the principles is merely conditional, for other ways of interpreting the same data can be conceived, and it is admitted that there are circumstances, however hard to specify exactly, in which it would have to be agreed that they do not apply.

Logical form of metaphysical arguments
      There is also the question whether metaphysical arguments are inductive (induction) or deductive (deduction) or whether they have some logical form peculiar to themselves. It is obvious that much metaphysical reasoning is, or purports to be, reasoning in the strict sense, which is to say that its form is deductive. Arguments like the first cause argument for God's existence claim to be demonstrations; their exponents believe that anyone who commits himself to the truth of the premises stands logically committed to the truth of the conclusions. This claim can stand, even if it turns out that the project to set out metaphysical results in the geometrical manner is a mistake. It may be impossible to model metaphysics on mathematics, but that does not make particular metaphysical arguments any less deductive.

      As regards inductive arguments, it would be odd to find a metaphysician contending, as, for example, historians regularly do, that p is true and q is true and therefore it is reasonable to conclude that r is true. To assess probabilities in the light of established facts is too cautious for the average metaphysical mind. Yet it would be wrong to deny that metaphysicians are preoccupied with facts. Their objective is to give a reasoned account of what exists or obtains, and for this purpose attention to fact is of course indispensable. It figures in metaphysical thinking at two stages. First, at the beginning, when the metaphysician is concerned to formulate his main thesis; here there is a move from what holds in a restricted sphere (the sphere of physics, for example) to what is supposed to hold generally, a move that is possible only if the theorist concerned has an interest in the sphere in question. To arrive at his own position the metaphysician must extrapolate from what goes on outside metaphysics, and this means that he must be sensitive to significant developments in at least some of the main fields of learning and areas of practical activity. But he needs this extra-philosophical knowledge for a second purpose too: in estimating the success of his own theories. In principle he must show that his interpretation of experience covers the facts in an adequate way, and for this purpose what experts in the different spheres take to be established is of crucial importance. Metaphysics is not an empirical science—the element of speculation it includes is too strong for that—but the metaphysician can no more ride roughshod over facts than the scientist can. At the least he must explain away phenomena that seem to count against his thesis, or indicate how they might be explained away. Whether he explains or explains away, he needs to know what the main phenomena are.

      Finally, it is sometimes said that metaphysics can make use of a form of argument that is neither deductive nor inductive but transcendental; a transcendental argument is supposed to proceed from a fact to its sole possible condition. A transcendental argument is simply a form of deduction, with the typical pattern: only if p then q; q is true; therefore, p is true. As this form of argument appears in philosophy, the interest, and the difficulty, reside not in the movement from premises to conclusions, which is absolutely routine, but in the setting up of the major premises—in the kinds of things that are taken as starting points. In Kant's case, it was such things as the possibility of pure mathematical knowledge, the possibility of making objectively true statements, the fact that there is a unitary system of time. Kant purported to prove a number of surprising propositions by the use of transcendental arguments; he tried to commend major premises such as his arguments about causality and substance by showing what would result if the protasis (i.e., p) did not hold. What he had to say under this head has attracted particular interest in recent years. It seems clear, however, that from the logical (applied logic) point of view no special significance attaches to this form of argument. Although Kant had been successful in demonstrating that a sufficient is also a necessary condition, he did not make clear why it should be taken as the sole such condition. There is an important gap in his reasoning here, as there is in that of other metaphysical writers.

Criticisms of metaphysics
      Metaphysics has many detractors. The man who aspires “to know reality as against mere appearance,” to use Bradley's description, is commonly taken to be a dreamer, a dupe, or a charlatan. Reality in this context is, by the metaphysician's own admission, something that is inaccessible to sense; as Plato explained, it can be discovered only by the pure intelligence, and only if the latter can shake itself free of bodily encumbrances. The inference that the metaphysical world is secret and mysterious is natural enough. Metaphysics in this view unlocks the mysteries and lets the ordinary man into the secrets. It is, not to put too fine a point on it, a study of the occult.

Metaphysics as knowledge of the supersensible
      That there are aspects of metaphysics that lend colour to this caricature can scarcely be denied. The language of Plato, in particular, suggests an absolute distinction between the deceitful world of appearances, which can never be an object of knowledge, and the unseen world of Forms, each of which is precisely what it appears to be. Plato urged his readers not to take seriously the things of sense; he told them that everything having to do with the senses, including the natural appetites and the life of the body, is unreal and unimportant. The philosopher, in his view, needs to live an ascetic life, the chief object of which is to cultivate his soul. Only if he does this, and follows a rigorous intellectual training, has he any hope of getting the eye of his soul fixed on true reality and so of understanding why things are what they are.

      Yet even this program admits of an innocuous, or relatively innocuous, interpretation. The “dialectician,” as Plato called his metaphysical philosopher, is said in one place to be concerned to “give an account,” and the only things of which he can give an account are phenomena. Plato's interest, despite first appearances, was not in the unseen for its own sake; he proposed to go behind things visible in order to explain them. He was not so much disdainful of facts as critical of accepted opinions; his attack on the acquiescence in “appearances” was an attack on conventional wisdom. That this was so comes out nowhere more clearly than in the fact that his targets included not just beliefs about what there is but also beliefs about what is good. It is the opinions of the many that need correction and that can happen only if men penetrate behind appearances and lay hold on reality.

      Plato is often presented as an enemy of science on the ground that he was bitterly opposed to Empiricism and because he said that, if there was ever to be progress in astronomy, the actual appearances of the starry heavens must be disregarded. He understood by Empiricism, however, the uncritical acceptance of apparent facts, with the attempt to trace regularities in them; it is an attitude that, in his view, is marked by the absence of thought. As for the starry heavens, it is certainly difficult to take Plato quite literally when he compares their function in astronomy to that of a well-drawn diagram in geometry. Yet he was not wrong to suggest that no progress could be made in astronomical inquiries until appearances were seen to be what they were and not taken for absolute realities. The subsequent progress of astronomy has shown this view to be entirely correct.

      There are respects in which Plato's attitude to phenomena was precisely the same as that of the modern scientist. The fact remains, nevertheless, that he believed in a realm of unseen realities, and he is of course far from being the only metaphysician to do so. Many, if not quite all, metaphysicians are committed to claiming knowledge of the supersensible, in some degree at least; even Materialists are alleged to make this claim when they say that behind the familiar world of everyday experience there lies material substance that is not accessible to the senses. It has been a commonplace among critics of metaphysics since the early 18th century that no such claims can be justified; the supersensible cannot be known about, or even known of, whether directly or by inference.

Specific criticisms
 An early but powerful statement of these criticisms is to be found in the writings of David Hume, A Treatise of Human Nature (1739–40) and An Enquiry Concerning Human Understanding (1748). Hume argued first that every simple idea was derived from some simple impression and that every complex idea was made up of simple ideas; innate ideas, supposed to be native to the mind, were nonexistent. There were eccentricities in Hume's conception of idea (and for that matter in his conception of impression), but these did not destroy the force of his argument that the senses provide the materials from which basic concepts are abstracted. A being that lacked sense experience could not have concepts in the normal sense of the term. Next, Hume proceeded to make a sharp distinction between two types of proposition, one knowable by the pure intellect, the other dependent on the occurrence of sense experiences. Propositions concerning matters of fact and existence answer the latter description; they either record what is immediately experienced through the senses or state what is taken to be the case on the basis of such immediate experiences. Such statements about matters of fact and existence are one and all contingent; their contradictories might have been true, though, as a matter of fact, they are not. By contrast, propositions of Hume's other type, which concern relations of ideas, are one and all necessary; reflection on the concepts they contain is enough to show that they must, in logic, be true. Though, in a sense, knowledge of these propositions is arrived at by the exercise of pure reason, no real significance attaches to this fact. It is not the case of some special insight into the nature of things; the truth is rather that these propositions simply make explicit what is implicit in the definitions of the terms they contain. They are thus what Kant was to call analytic propositions, and it is an important part of Hume's case that the only truths to which pure reason can attain are truths of this nature.

      Finally, Hume sought to block the argument that, even if the supersensible could not be known directly, or through pure intellectual concepts, its characteristics could, nevertheless, be inferred. His analysis of causality had this as one of its aims. According to Hume, the only means by which men can go beyond the impressions of the memory and the senses and know what lies outside their immediate experience is by employing causal reasoning. Examination of the causal relation, however, shows that it is, among other things, always a relation of types of events in time, one of which invariably precedes the other. Causality is not, as Descartes and others supposed, an intelligible relation involving an internal tie between cause and effect; it is a matter of purely factual connection and reduces on its objective side to nothing more than regular precedence and succession. The importance of this for the present inquiry lies in the consequence that causal relations can hold only between items, or possible items, of experience. According to Hume, if the temporal element is removed from causality, nothing concrete is left; if it is kept, it becomes impossible to argue that one can proceed by causal reasoning from the sensible to the supersensible. Yet it was precisely this that Aristotle, Thomas Aquinas, and Locke had all attempted.

      Hume's own explicit pronouncements about metaphysics are ambivalent. There is a famous passage in which he urged men to consign volumes of divinity and “school metaphysics” to the flames, “as containing nothing but sophistry and illusion,” but in at least one other place he spoke of the need to “cultivate true metaphysics with some care, in order to destroy the false and adulterate.” “True metaphysics,” in this connection, meant critical philosophical reflection.

      Hume's successor Kant made a sharper distinction between metaphysics and critical philosophy. Much of Kant's philosophical effort was devoted to arguing that metaphysics, understood as knowledge of things supersensible, is an impossibility. Yet metaphysics, as a study of the presuppositions of experience, could be put on “the sure path of science”; it was also possible, and indeed necessary, to hold certain beliefs about God, freedom, and immortality. But however well founded these beliefs might be, they in no sense amounted to knowledge: to know about the intelligible world was entirely beyond human capacity. Kant employed substantially the same arguments as had Hume in seeking to demonstrate this conclusion but introduced interesting variations of his own. One point in his case that is especially important is his distinction between sensibility as a faculty of intuitions and understanding as a faculty of concepts. According to Kant, knowledge demanded both that there be acquaintance with particulars and that these be brought under general descriptions. Acquaintance with particulars was always a matter of the exercise of the senses; only the senses could supply intuitions. Intuitions without concepts, nevertheless, were blind; one could make nothing of particulars unless one could say what they were, and this involved the exercise of a very different faculty, the understanding. Equally, however, the concepts of the understanding were empty when considered in themselves; they were mere forms waiting to be brought to bear on particulars. Kant emphasized that this result held even for what he called “pure” concepts such as cause and substance; the fact that these had a different role in the search for knowledge from the concepts discovered in experience did not give them any intuitive content. In their case, as in that of all other concepts, there could be no valid inference from universal to particulars; to know what particulars there were in the world, it was necessary to do something other than think. Thus is revealed the futility of trying to say what there is on the basis of pure reason alone.

      Kant's distinction between analytic and synthetic propositions has peculiarities of its own, but for present purposes it may be treated as substantially identical with Hume's distinction set out above. Similarly, the important differences between Kant and Hume about causality may be ignored, seeing that they agreed on the central point that the concept can be properly applied only within possible experience. If it is asked whether there are substantial differences between the two as critics of metaphysics, the answer must be that there are but that these turn more on temperament and attitude than on explicit doctrine. Hume was more of a genuine iconoclast; he was ready to set aside old beliefs without regret. For Kant, however, the siren song of metaphysics had not lost its charm, despite the harsh words he sometimes permitted himself on the subject. Kant approached philosophy as a strong believer in the powers of reason; he never abandoned his conviction that some of man's concepts are a priori, and he argued at length that the idea of the unconditioned, though lacking constitutive force, had an all-important part to play in regulating the operations of the understanding. His distinction between phenomena and noumena, objects of the senses and objects of the intelligence, is in theory a matter of conceptual possibilities only; he said that, just as one comes to think of things sensible as phenomena, so one can form the idea of a world that is not the object of any kind of sense experience. It seems clear, however, that he went beyond this in his private thinking; the noumenal realm, so far from being a bare possibility invoked as a contrast with the realm that is actually known, was there thought of as a genuine reality that had its effects in the sense world, in the shape of moral scruples and feelings. A comparison of what was said in Kant's early essay Träume eines Geistersehers erläutert durch Träume der Metaphysik (1766; Dreams of a Spirit-Seer), with the arguments developed in the last part of his Grundlegung zur Metaphysik der Sitten (1785; Fundamental Principles of the Metaphysic of Morals), would seem to put this judgment beyond serious doubt.

      Though Kant remained convinced of the existence of things supersensible, he, nonetheless, maintained throughout his critical writings that there can be no knowledge of them. There can be no science of metaphysics because, to be true to fact, thinking must be grounded in acquaintance with particulars, and the only particulars with which human beings are acquainted are those given in sense. Nor was this all. Attempts to construct metaphysical systems were constantly being made; philosophers repeatedly offered arguments to show that there must be a first cause, that the world must consist of simple parts, that it must have a limit in space, and so on. Kant thought that all such attempts could be ruled out of court once and for all by the simple expedient of showing that for every such proof there was an equally plausible counterproof; each metaphysical thesis, at least in the sphere of cosmology—i.e., the branch of metaphysics that deals with the universe as an orderly system—could be matched with a precise antithesis whose grounds seemed just as secure, thus giving rise to a condition that he called “the antinomy of pure reason.” Kant said of this antinomy that “nature itself seems to have arranged it to make reason stop short in its bold pretensions and to compel it to self-examination.” Admittedly, the self-examination led to more than one result: it showed on the one hand that there could be no knowledge of the unconditioned and demonstrated on the other that the familiar world of things in space and time is a mere phenomenon, thus—to Kant—clearing the way to a doctrine of moral belief. Though this doctrine could not be expunged from Kant's philosophy without destroying it altogether, it is quite wrong to present it, as some modern German writers do, as amounting to the advocacy of an alternative metaphysics. What Kant was concerned with here is what must be thought, not what can be known.

Logical Positivists
 Despite what has just been said, it must be admitted that Kant's constant talk about the supersensible makes many critics of metaphysics regard him as a dubious ally. This was certainly true in the case of the Logical Positivists, the philosophical school that has attacked metaphysical speculation most sharply in the 20th century. The Positivists derived their name from the “positive” philosophy of Auguste Comte, a 19th-century Frenchman who had represented metaphysical thought as a necessary but now superseded stage in the progression of the human mind from primitive superstition to modern science. Like Comte, the Logical Positivists thought of themselves as advocates of the cause of science; unlike Comte, they took up an attitude toward metaphysics that was uniformly hostile. The external reason for this was to be found in the philosophical atmosphere in the German-speaking world in the years following World War I, an atmosphere that seemed to a group of thinkers known as the Vienna Circle to favour obscurantism and impede rational thought. But there were, of course, internal reasons as well.

      According to the Positivists, meaningful statements can be divided into two kinds, those that are analytically true or false and those that express or purport to express matters of material fact. The propositions of logic and mathematics exemplify the first class, those of history and the natural and social sciences the second. To decide whether a sentence that purports to state a fact is meaningful, one must ask what would count for or against its truth; if the answer is “nothing,” it cannot have meaning, or at least not in that way. Thus, they adopted the slogan that the meaning of a (nonanalytic) statement is the method of its verification. It was this verification principle that the Positivists used as their main weapon in their attacks on metaphysics. Taking as their examples statements from actual metaphysical texts—statements such as “The Absolute has no history” and “God exists”—they asked first if they were supposed to be analytically or synthetically true, and then, after dismissing the first alternative, asked what could be adduced as evidence in their favour or against them. Many metaphysicians, of course, claimed that there was empirical support for their speculative conclusions; thus, as even Hume said, “the order of the universe proves an omnipotent mind.” The very same writers, however, proved strangely reluctant to withdraw their claims in the face of unfavourable evidence; they behaved as if no fact of any kind could count against their contentions. It followed, said the Positivists, that the theses in which they were interested were compatible with any facts whatsoever and thus were entirely lacking in significance. An analytic proposition, such as “It either will or will not rain tomorrow,” tells nothing, though there may be a point in giving voice to it. A metaphysical proposition claims to be very different; it purports to reveal an all-important truth about the world. But it is no more informative than a bare tautology, and, if there is a point in putting it forward, it has to do with the emotions rather than the understanding.

      In point of fact, the Positivists experienced great difficulty in devising a satisfactory formulation of their verification principle, to say nothing of a satisfactory account of the principle's own status. In the early days of the movement the demand for verifiability was interpreted strictly: only what could be conclusively verified could be significant. This had the effect of showing that statements about the past and propositions of unrestricted generality, to take only two instances, must be without meaning. Later a move was made toward understanding verifiability in a weak sense: a statement was meaningful if any observations bore on its truth. According to A.J. Ayer, an English disciple of the Vienna Circle, writing in 1936,

It is the mark of a genuine factual proposition, not that it should be equivalent to an experiential proposition, or any finite number of experiential propositions, but simply that some experiential propositions can be deduced from it in conjunction with certain other premises without being deducible from those other premises alone.

      As Ayer admitted in his second edition, however, this formulation lets in too much, including the propositions of metaphysics. From “The Absolute has no history” and “If the Absolute has no history, this is red,” it follows that “This is red,” which is certainly an experiential proposition. Nor were subsequent attempts, by Ayer and others, to tighten up the formulation generally accepted as successful, for in every case it was possible to produce objections of a more or less persuasive kind.

      This result may seem paradoxical, for at first glance the Positivist case is extremely impressive. It certainly sounds odd to say that metaphysical sentences are literally without meaning, seeing that, for example, they can be replaced by equivalent sentences in the same or another language. But if the term meaning is taken here in a broad sense and understood to cover significance generally, the contention is by no means implausible. What is now being said is that metaphysical systems have internal meaning only; the terms of which they consist may be interdefinable but perhaps do not relate to anything outside the system. If that were so, metaphysics would in a way make sense but for all that would be essentially idle; it would be a game that might amuse but could hardly instruct. The Positivists confront the metaphysician with the task of showing that this criticism is not correct. Whatever difficulties are involved in formulating a principle of verifiability, the challenge can hardly be ignored.

Moore and Wittgenstein
      The Positivists were not the only modern critics of metaphysics. G.E. Moore never argued against metaphysics as such, but nevertheless he produced criticisms of particular metaphysical theses that, if accepted, would make metaphysical speculation difficult, if not impossible. It was characteristic of a certain type of philosopher, according to Moore, to advance claims of a highly paradoxical nature—to say, for instance, that “Time is not real” or that “There are no such things as physical objects.” Moore's case for rejecting such claims was that they go against the most central convictions of common sense, convictions that people accept unhesitatingly when they are not doing philosophy. Men constantly say that they did this before that, that things are better or worse than they were; from time to time they put off things until later or remark that tomorrow will be another day. Moore took these facts as definitive proof of the reality of time and definitive disproof of any metaphysical theory that denied it. Supporters of Bradley, the philosopher here criticized, replied that Moore had missed the point. Bradley never denied the truth of temporal propositions as used in the description of appearances; what he questioned was the coherence and ultimate tenability of the whole temporal way of thinking. As Rudolf Carnap, a Logical Positivist, was to put it, he raised an external question and was given an internal answer by Moore. It was an answer, however, that carried considerable conviction. The simple denial of what seem to be obvious facts had always been part of the stock-in-trade of metaphysicians; they make much of the distinction between appearance and reality. Moore may not have demonstrated the impropriety of this insistence, but at least he made it necessary for the metaphysician to be more circumspect, to explain explicitly what he was denying and what he was ready to accept, and so to make his own case sharper and thus easier to confirm or reject.

 Moore's implied criticisms of metaphysics lead on naturally to those of Wittgenstein. Moore took his stand on common sense, whereas Wittgenstein based his on living language. Arguing that men are each involved in a multitude of language games or autonomous linguistic activities, insofar as they are scientific investigators, moral agents, litigants, religious worshipers, and so on, Wittgenstein asked in what language game the claims and questionings of philosophers arose. He replied that there was no genuine linguistic context to which they belonged; philosophical puzzlement was essentially idle. Philosophers were preoccupied with highly general questions; they aspired to solve the problem of meaning or the problem of reality. Against that Wittgenstein argued that words and sentences have meaning as used in particular contexts; there is no single set of conditions that has to be fulfilled if they are to be thought meaningful. Equally, there is no single set of criteria that has to be satisfied by everything one takes to be real. Sticks and stones and men are taken as real in everyday discourse, but so are numbers in the discourse of mathematicians, and so is God in the discourse of religious men. There is simply no warrant for preferring one of these above the others—for saying, for example, with persons of an Empiricist turn of mind, that nothing can be real that does not have existence in space and time.

      Wittgenstein's antipathy to metaphysical philosophy was in part based on self-criticism; in his early work the Tractatus Logico-Philosophicus, published in 1922, he had himself tried to give a general account of meaning. At least one doctrine of that enigmatic book survived in his later thought: the distinction between saying and showing. Wittgenstein in the Tractatus sought to pronounce on “what can be said” and came to the conclusion that only “propositions of natural science” can be. Though at this stage he spoke as if metaphysical statements were senseless, his motives for doing so were very different from those of the Positivists. The latter saw metaphysics as an enemy of science; in their view there was only one way to understand the world, and that was in scientific terms. But Wittgenstein, though agreeing that science alone can be clear, held that scientific thought has its limitations. There are things that cannot be said but can, nonetheless, be shown; the sphere of the mystical is perhaps a case in point. Unlike his Viennese contemporaries, Wittgenstein had no wish to rule out of court the thought that there are more things in heaven and earth than can be compassed in the language of science; writers whom he admired—such as Blaise Pascal, a 17th-century French scientist and writer on religious subjects, and Søren Kierkegaard, a Danish philosopher and theologian who is regarded as the founder of modern Existentialism—had discoursed of such matters in a way that was highly illuminating. They had made clear, however, that, just as one here went beyond the province of science, so also one went beyond that of philosophy. For them the idea that the metaphysician is privy to the most important of all things is absurd. There may be a sense in which men transcend everyday experience in moments of religious feeling or artistic insight, but there is no justification for thinking that when they do they arrive at the metaphysician's Absolute. As Kierkegaard said, the man who looks for speculative proofs in the sphere of religion shows that he does not understand that sphere at all.

Religious philosophers
      It is important, in considering current criticisms of metaphysics, to appreciate that this discipline is now under double attack. In the first place, it must face the assault of those who regard it as a rival to science; it is against this assault that sympathizers like R.G. Collingwood, a British philosopher, historian, and archaeologist, seek to defend it. But metaphysics is also in disfavour among many religious philosophers. In earlier days, partisans of religion, and more generally believers in a spiritual order, looked to metaphysics to vindicate their claims against skeptical attack; now they are altogether more reluctant to do so. The continuing controversy about metaphysics has no doubt influenced this development; it scarcely seems sensible to take refuge in a fortress whose walls are so frequently breached. There is, however, another motive that operates here: the feeling that metaphysics is not only dubious but, worse, unnecessary. In an age whose tendencies are antiphilosophical rather than philosophical, there is widespread acceptance of the view that religion and morals, and for that matter science and history, are their own justification; none of them stands in need of a certificate of respectability from philosophy, and any pretense by metaphysicians to supply or refuse such a certificate must be without foundation. Though this view is widespread, it is even so not unchallenged; there are persons who find the fragmentation it involves—belief in God on Sundays, belief in science for the rest of the week—intolerable. For such persons, at least, the search for metaphysical truth and metaphysical answers must retain its fascination.

William Henry Walsh

Tendencies in contemporary metaphysics

Tendencies in the United States
      Kant's efforts to limit metaphysics opened new lines for its development. He had thought that reason is established by being limited and that some truths are certain independent of anything that can happen in experience because experience is structured by the interpretive categories reflected in these truths. Thus, it is possible to be certain of the world in its general structure but only insofar as it is an experienced, or phenomenal, world—that is, a world known by man, not a world as it is in itself. Hegel (Hegel, Georg Wilhelm Friedrich), however, argued persistently that knowledge of a thing unknowable in itself is a contradiction and that reason can know all that is real if the mind first accepts the given thing as “always already within experience as other.” The mutual implication of knowing mind and reality known is accepted, and a science of self-consciousness that relates all categories and all reality to the knowing subject is envisaged. Thus, Kant's mutual implication of knowing subject and phenomenal thing was given ultimate metaphysical validity by Hegel, and Kant's reformulations of traditional dualisms—e.g., subject–object, appearance–reality, perceptual–categorial, immanent–transcendent, regulative–constitutive—became momentous for metaphysics.

John Dewey (Dewey, John)
 In this milieu, John Dewey, an American educational reformer and pragmatic philosopher, published his “Kant and Philosophic Method” in 1884 in the journal of a group known as the St. Louis Hegelians. Although Dewey later rejected the full-scale Hegelianism expressed in the article, he did so only after gathering up in a partial synthesis the thought of both Kant and Hegel. In this he sounded the thematic notes of much contemporary American and continental metaphysics. Whether or not this metaphysics is explicitly termed transcendental (that is, concerned with experience as determined by the mind's conceptual and categorial makeup), it does two things: (1) it affirms Kant's insight that physical particulars cannot first be identified and later interrelated by means of the categories, but, to be identified at all, they must be assumed to be already categorized, and reasoning must proceed to expose those categorial structures that make the actuality of knowledge possible; (2) it agrees with Hegel's critique at least to the extent that Kant's idea that the source of sensations is external to the mind in a noumenon is regarded as a transgression of Kant's own doctrine that the categories, particularly that of causation, can be applied only within phenomenal experience. Dewey thought that Kant confused the empirical and transcendental standpoints by mixing analysis of the organism as sensationally responsive with analysis of mind. Kant (Kant, Immanuel) forgot that it is only because the knowing subject already grasps the world through its categories that it can self-deceivingly regard its sensations as subjective and as caused by something not known. Thus, for Dewey, “The relation between subject and object is not an external one; it is one in a higher unity that is itself constituted by this relation.”

      In Dewey's extended later thought, metaphysics became the study of “the generic traits of existence.” Concern with God and immortality slips nearly from view, and this is typical of much contemporary philosophy. Even so, Dewey's rethinking of the subject–object relation engenders a concept of a democratic and scientific community of persons, bound to each other through common ideals, which has religious overtones. Vague and ambivalent as this concept may be, it helps undermine the whole contrast between immanent and transcendent and leads metaphysics on new paths.

William James (James, William)
      The work of William James, a leader of the Pragmatic movement, was typical of many contemporary tendencies, one of which was the attempt to locate the role of science in knowledge and culture. Trained in medicine, James hoped to protect the autonomy of psychology as a science by adopting a dualistic view of mind and matter. He “supposes two elements, mind knowing and thing known, and treats them as irreducible. Neither gets out of itself or into the other, neither in any way is the other.” He presumed that mental states could be identified independent of a commitment to the metaphysical status of the things known by them and that they could then be correlated to the brain. Ironically, his attempts to identify mental states involved him in commitments to the nature of the world as presented to mind. The only meaning that can be given things is in terms of the anticipated consequences of one's actions upon these things in the world; this anticipation also supplies the meaningfulness of thoughts. This is the basis of the “instrumental” view of thoughts—i.e., reflecting upon thoughts as “tools,” or as “plans of action,” tells one something about the things known by them, the “tooled”; the converse also occurs.

      Each realm of the world is experienced in terms of temporal standards of thought natural to that realm; e.g., standards of mathematics are peculiar because of their ideal, changeless objects. These criteria are not derived from mind alone or from things alone but from their relationship in what is termed experience. This is a “double-barreled” term—that is, an experiencing of experienced things. The mind cannot be specified independent of things that appear to the mind, and things cannot be specified independent of their modes of appearing to the mind. Phenomena regarded abstractly as singular, or “pure,” are neutral between mind and matter, which are different contexts of the very same pure experiences—contexts that comprise a single world.

      James would not claim that his method is transcendental. Yet the fact remains that for him subject and object cannot be specified independent of each other, and James undercuts dualism and moves toward a transcendental explanation of the conditions of knowledge.

      James tried to avoid what can be called logicism, physicalism, and psychologism. The last claimed that, because knowing is a psychical act, all that is known about must be subject to psychological laws. James replied that the known-about, the experienced, has its own autonomy, either as pure experience, a “specific nature” studied by philosophy, as a physical context studied by physics, or, finally, as a psychical context, a human history, studied by psychology. The latter two are both dependent, at least for their ultimate meaningfulness, upon the first. Physicalism attempts to infer the nature of the psychical directly from the physical, thus reducing it to the physical. Most logicisms claimed that pure reason can grasp the real in itself. James agreed that reason entertains ideal objects, the relations between which are fixed independent of the sequence of sensory experience, but he asserted that this experience must decide which necessary truths apply to the world. Although some always do apply, the ascertainment of what is categorial for the world is always incomplete. Just when the world “plays into the hands of logic” is decided in that endless interaction of “worlds” or “orders of experience”—such as the perceptual, the imaginary, the mathematical—occasioned by a thing experienced sifting through the orders trying to find one that can contain it without contradiction; Pegasus, for example, is a mythical creature just because it cannot find a place in the world of real horses. The world of perceptual things, experienced as experienceable by all and as existing simultaneously, serves as a paradigm of reality even though other orders of experience are not reducible to it. Existence is an unusual predicate for James; it means that practical relationship of doing and concern within which things must be able to stand to men if they are to be counted as fundamentally real. James was not giving a subjectivistic account of reality, however, because he included in the fundamentally real all that can be related spatially and temporally to what can stand over against men's bodily selves. This was commonly forgotten by critics of James's popularized theory of truth, Pragmatism, which was thus systematically misunderstood.

      James's contemporaries Charles Sanders Peirce (Peirce, Charles Sanders) and Josiah Royce (Royce, Josiah) stood in close dialectical exchange with him on these themes. Differences between them concerned the scope and conditions to be assigned experience. In general, Peirce argued that experience is to be construed more narrowly, in terms of mathematical logic and physics, whereas Royce argued that the understanding of truth, error, and meaning requires the assumption of an absolute knower or experiencer. Peirce was a seminal thinker whose thoughts were often beginnings in the more systematically developed philosophies of the other Americans.

Tendencies in continental Europe
Edmund Husserl (Husserl, Edmund) and Phenomenology
 Edmund Husserl, the German philosopher, used the term Phenomenology to name a whole philosophy. In order to rid his transcendental investigation of empirical prejudgments and to discover connections of meaning that are necessary truths underlying both physical and psychological sciences, Husserl bracketed and suspended all judgments of existence and empirical causation. He did not deny them; rather, he no longer simply asserted them. He reflected upon their intended meaning. In reflection he claimed to see that things have meaning in terms of how they appear to men in their pre-reflective life and that awareness is in terms of this “how.” In pre-reflective life, however, men are not aware of the “how” as such. By exposing this basic meaning through which men refer to things, he can free their eyes of the “cataracts” of the stereotyped and the obvious and can summon them “back to the things themselves.”

      Husserl took traditional metaphysics to be infested with precritical commitments to existence, either physicalistic, psychologistic, or logistic. He used the term ontology, however, to apply to his study of objects of consciousness and even appropriated the Aristotelian term first philosophy. The world appears within the reflective bracket as existentially neutral (that is, as regards whether things have existence in themselves or exist for men) but ontologically ordered because, if various orders of beings exist, then what they are can be nothing but what they are intended to be. And what they are cannot be known until all they are intended to be is known.

      Husserl distinguished two types of ontologies: formal ontologies, which are the domain of meanings, or essences, such as “one,” “many,” “whole,” or “part,” that are articulated by formal logic and which Husserl referred to as empty; and material ontologies, which discover and map the meaning and structure of sensory experience through transcendental investigation. In material ontology, for example, the essence of any physical thing is discovered by varying in the imagination the object that is given within its strictly correlative mode of perceptual consciousness; the essence is that identical something that continuously maintains itself during the process of variation. It is intuited that the perceived thing cannot vary in the imagination beyond the point of something given perspectively and incompletely to any given perceiving glance; hence, this is the essence of any physical thing. This is a truth of eidetic necessity and comprises a first principle in Husserl's projected philosophical science; e.g., numbers are what they are because of the ways in which they are not like things.

The Existentialists (Existentialism)
      Husserl had early distinguished the primary task of description of “morphological essences” (those with “floating” spheres of application in the sensory life) from description of essences like those in geometry, which described closed, or definite, manifolds; but the question of the theoretical status of the ordinary perceptual world, or lived world (life-world) (Lebenswelt), became increasingly disputed among Existentialists. They asked whether there can be a philosophical science that has made all its presuppositions transparent to itself. If transcendental elucidation of the Lebenswelt, with its historically established sediments of meaning, is really essential to show how theoretical sciences are grounded, then one may reasonably ask how Phenomenology can be sure it has accomplished the elucidation completely because it is itself a theory. The question gained urgency by Husserl's nearly imperceptible slide into what appeared to be an Idealist position regarding the source of all meaning, a commitment to an absolute ego. If this ego is regarded as individual in any way, the problem arises of how any other individual can be as other because it is constituted in this primal ego.

      Husserl's theory of the ego was rejected by French Existentialists such as Jean-Paul Sartre and Maurice Merleau-Ponty (Merleau-Ponty, Maurice). For the latter, the bracketing of meanings can never be completed, for consciousness is not an enclosed individual that could grasp through reflection all its possible motivations to experience and give meaning to a world. Knowers are subjects with bodies, whose perceptual life is articulated only incompletely and discloses the world in progressively surprising ways. More meaning is found in existence than can at any moment be expressed, and even the meaning of existence is not reducible to any definable set of meanings.

 Husserl's approach was not nearly radical enough for Martin Heidegger (Heidegger, Martin), a German thinker sometimes called an Existentialist. In thinking that he could prescind so neatly from facts and retain the essence of facts, Husserl was still involved to some extent in the prejudgments—the psychologistic, physicalistic, and logistic dualisms—that he inveighed against. For Heidegger there is no realm of consciousness that constitutes meaning, and he does not think that some sharp but harmless line could be drawn between essence and fact. The ambiguity in Husserl's thought between “object” as sense of the particular and as the encountered particular in its bodily presence is not harmless. It is unjustifiable to think that consciousness can finally demarcate the essential sense of a thing. Thus, Heidegger discarded the very concept of consciousness and proposed a “fundamental ontology” of human being (Dasein). Man as a subject in the world cannot be made the object of sophisticated theoretical conceptions such as “substance” or “cause”; man, furthermore, finds himself already involved in an ongoing world that cannot as a whole be made the object of such conceptions; yet the structure of this involvement is the transcendental condition of any science of objects. For example, a man can band with other men in philosophical groups and can think about the metaphysical status of other men only because he is already essentially with others. He cannot hope to so purify his own thinking that it becomes that of an impersonal thinker, an absolute ego.

      According to Heidegger, to rethink the problem of reality at its roots, it is necessary to rethink the fundamentally temporal, already-given structures of human involvement. Prejudice in the West, which construes reality, or being, on the basis of beings (that is, being as the most general feature of beings), must be overturned, and the problem of the real, the “transcendent,” must be rethought on a ground on which distinctions between immanent and transcendent and between perceptual and categorial have been reconstructed. The being of the world transcends any constitution of the meaning of the world and is a condition of experience. Thus, a sense is required of being not as object but as the underlying condition for the reality of the being of all objects.

      Heidegger wanted to propose a genuine phenomenology, a study that would presuppose nothing of the traditionally formulated distinctions such as subjective–objective or phenomenal–real. The transcendence of the world can be understood only as it appears; i.e., when they are encountered openly, things appear as appearing in part, as both revealing and concealing themselves. If to the uneducated eye the Sun appears to be smaller than it is, the naive inference can be corrected only by educating the person to interpret appearances—to calculate, for example, the speed and direction of light. The real is given in and through its appearances.

The thought of Whitehead
      The thought of Alfred North Whitehead (Whitehead, Alfred North) is a distinctive variation on these contemporary themes. Dualisms (dualism) are undermined by a phenomenology that does not bracket factual assertions. Logical and mathematical deductive schemes must be able to be interpreted in relationships crudely observable in experience, and abstractions of physics and common sense parading as realism (e.g., that things exist separately within their own surfaces) must be revealed for what they are, namely, abstractions. The basic units of reality are organismic unities, “actual occasions,” which are spatial and temporal extensions that cannot be exhaustively expressed in terms of distributions of matter at an instant. Their unity is constituted in a perception-like responsiveness to the universe that, though usually lacking consciousness or apprehension, is an appropriation to and for itself of the whole. This appropriation cannot be exhaustively expressed by point-instant mechanics (mechanics that is worked out in connection with the physics of relativity and thus measures not only the distance but also the time intervals between points) but is minimally a “prehension” (a term proper to Whitehead indicating the point-transcending function of perception and consciousness).

      Each enduring object of ordinary perception—tables, chairs, animals—is, for Whitehead, a “society” of actual occasions inheriting, through a process of appropriation and reenactment in a predictable way, characteristics of its predecessors. Human perception is understood as a special case of prehension, in which qualities of the environment are mediated and projected on the basis of organic and affective experience of the perceiver's body, but in such a way that some of this process can be acknowledged by the percipient upon reflection. Because human consciousness is regarded as only a special case of prehensive relations, and because vacuous realisms and notions of transcendence are regarded as “fallacies of misplaced concreteness and simple location,” mind–body dualisms are rejected.

      Whitehead thought of “the primordial nature of God” as a general ordering of the process (process philosophy) of the world, the ultimate basis of all induction and assertion of law, a “conceptual prehension” that functions in the selection of those “eternal objects,” or repeatable patterns that are enacted in the world. God, however, does not create actual entities. He provides them with initial impetus, in the form of their subjective aim, to self-creation. Even God is the outcome of creativity, the process by which the events of the world are synthesized into new unities. It is the creative, not fully predictable, advance into novelty of a pluralistic process. The freedom of man and the determinism of nature were regarded by Whitehead as another artificial dualism.

      The future of metaphysics is uncertain, not mainly because of 20th-century critics, the Logical Positivists, but because of its own not fully predictable nor controllable dynamisms.

Bruce Withington Wilshire

Additional Reading
These works deal mainly with the nature and possibility of metaphysics.For a discussion of the apparently conflicting views of Plato and Aristotle, see the commentary in Aristotle, Metaphysics, ed. by W.d. Ross, rev. ed., 2 vol. (1924, reissued 1966); and Werner Jaeger, Aristotle: Fundamentals of the History of His Development, 2nd ed. (1948, reprinted 1968; originally published in German, 1923). Modern discussions of the methods of metaphysics are found in René Descartes, The Philosophical Works of Descartes, trans. by Elizabeth S. Haldane and G.R.T. Ross, 2 vol. (1911–12, reprinted with corrections, 1981), and Philosophical Letters, trans. from the French and ed. by Anthony Kenny (1970). On the geometrical form of metaphysics, see the essay by Benedict Spinoza, “Ethica, more geometrico demonstratis,” available in a translation by W. Hale White and rev. by Amelia H. Stirling, Ethic: Demonstrated in Geometrical Order . . . , 4th ed. rev. (1927, reprinted 1930). Christian Wolff combined both the practice and theory of metaphysics in his voluminous metaphysical writings: Vernünfftige [sic] Gedanken von Gott, der Welt und der Seele der Menschen, new enlarged ed. (1751, reprinted 1983), Philosophia Prima Sive Ontologia, 2nd ed. (1736, reprinted 1962), Cosmologia Generalis, rev. ed. (1737, reprinted 1964), Psychologia Rationalis, rev. ed. (1740, reprinted 1972), and Theologia Naturalis, rev. ed., 2 vol. (1739–41, reprinted 2 vol. in 3, 1978–81). Alexander Gottlieb Baumgarten, Metaphysica, 7th ed. (1779, reprinted 1963), was in effect a digest of these last four works. The problem of the origin of ideas was first posed in John Locke, An Essay Concerning Humane [sic] Understanding (1690, reissued 1979), on which G.W. Leibniz wrote a critical commentary, Nouveaux essais sur l'entendement humain (1765), available also in an English translation ed. by Peter Remnant and Jonathan Bennett, New Essays on Human Understanding (1981). George Berkeley criticized Materialism in his Treatise Concerning the Principles of Human Knowledge (1710, reissued 1983), available also in a contemporary edition ed. by Colin M. Turbayne. David Hume applied Empiricist principles with complete generality in A Treatise of Human Nature, 3 vol. (1739–40, reprinted in 1 vol., 1975), and An Enquiry Concerning Human Understanding (1748, reissued 1977).Immanuel Kant first discussed metaphysical method in his essay “Inquiry into the Distinctness of the Principles of Natural Theology and Morals,” available in a translation by Lewis White Beck, Critique of Practical Reason and Other Writings in Moral Philosophy (1949); and Kant examined the whole question of the possibility of metaphysical knowledge in Critique of Pure Reason (1982; originally published in German, 4th ed., 1794), and Prolegomena to Any Future Metaphysics That Will Be Able to Come Forward as Science, trans. by Paul Carus (1902, rev. ed. 1977). For a sustained criticism of Kant's critical point of view, see the writings of G.W.F. Hegel, especially The Phenomenology of Mind, 2nd ed. (1931, reissued 1977; originally published in German, 1807), The Logic of Hegel, trans. from the German by William Wallace (1873, reprinted with the title Hegel's Logic, 1975), Hegel's Philosophy of Nature, 3 vol., ed. and trans. from the German by M.J. Petry (1970), and Hegel's Philosophy of Mind, trans. from the German by William Wallace, enlarged ed. (1971). These last three are translations from various editions of Hegel's Encycklopädie der philosophischen Wissenschaften, first published in 1817.Only a few 19th-century philosophers added to the fundamental criticisms of metaphysics developed by earlier writers. See, for example, Auguste Comte, Cours de philosophie positive, 6 vol. (1830–42), available also in an edition of selections, ed. by Stanislav Andreski, The Essential Comte (1974); and John Stuart Mill, System of Logic, 2 vol. (1843, reissued 1978). Mill was sharply criticized by Thomas Hill Green, Prolegomena to Ethics, 5th ed. (1907, reprinted 1969); and F.H. Bradley, The Principles of Logic, 2nd ed. rev. (1922, reissued 1963).For American metaphysical thought of the same period, see Charles Sanders Peirce, Collected Papers of Charles Sanders Peirce, ed. by Charles Hartshorne, Paul Weiss, and A.W. Burks, 8 vol. (1931–58, reissued in 4 vol., 1974–79); and William James, A Pluralistic Universe (1909, reprinted 1979).There are interesting remarks on the philosophy of philosophy in the works of Wilhelm Dilthey, especially vol. 5 of his Gesammelte Schriften, 5th ed., 12 vol. (1962). Twentieth-century criticisms of metaphysics derive mainly from the work of the Vienna Circle; see Viktor Kraft, The Vienna Circle: The Origin of Neo-Positivism (1953, reissued 1969; originally published in German, 1950). Ludwig Wittgenstein, Tractatus Logico-Philosophicus (1922, reissued 1983), was read as an improved version of Empiricism. Among the authors who influenced the Logical Positivists were Ernst Mach, The Science of Mechanics: A Critical and Historical Accident of Its Development, 6th ed. (1974; originally published in German, 9th ed., 1933); Alfred North Whitehead and Bertrand Russell, Principia Mathematica, 2nd ed., 3 vol. (1925–27, reprinted 1968–73); and Bertrand Russell, Our Knowledge of the External World as a Field for Scientific Method in Philosophy, rev. ed. (1926, reprinted 1972). A.J. Ayer (ed.), Logical Positivism (1959, reprinted 1978), anthologizes in translation some of the most famous papers from the Vienna Circle's periodical Erkenntnis. Ayer's own book, Language, Truth and Logic, 2nd ed. rev. (1946, reprinted 1970), was extremely successful in spreading Positivist ideas in America and Britain, where the work of George Edward Moore, especially “Defence of Common Sense,” in his Philosophical Papers, pp. 32–59 (1959, reprinted 1977), had created an atmosphere in which metaphysical claims were viewed with suspicion. Another influential book along the same lines as Ayer's was Hans Reichenbach, The Rise of Scientific Philosophy (1951, reprinted 1968); see also Morris Lazerowitz, The Structure of Metaphysics (1955, reprinted 1968), which attempts to explain the activities of metaphysicians in terms of psychoanalysis. For criticism of Positivist ideas, see Winston H.F. Barnes, The Philosophical Predicament (1950); D.F. Pears (ed.), The Nature of Metaphysics (1957, reprinted 1970); and Karl R. Popper, Conjectures and Refutations: The Growth of Scientific Knowledge, 4th ed. rev. (1974). R.G. Collingwood, An Essay on Metaphysics (1940, reprinted 1979), purports to answer Ayer but instead contains an unconventional view of metaphysics as historical analysis. A division of metaphysical systems into “descriptive” and “revisionary” is proposed in P.F. Strawson, Individuals: An Essay in Descriptive Metaphysics (1959, reprinted 1964). For further discussions, see W.H. Walsh, Metaphysics (1963, reprinted 1966); A.J. Ayer, Metaphysics and Common Sense (1969, reprinted 1973); Anthony Quinton, The Nature of Things (1973, reprinted 1978); Stephan Körner, Metaphysics, Its Structure and Function (1984); and D.W. Hamlyn, Metaphysics (1984). For a very different approach, compare Martin Heidegger, An Introduction to Metaphysics (1959, reissued 1961; originally published in German, 1953).Recent European thought is summarized in Rüdiger Bubner, Modern German Philosophy (1981), trans. by Eric Matthew from an unpublished manuscript, which provides a critical survey of recent philosophy in Germany and compares it to philosophical work in the English-speaking world; Vincent Descombes, Modern French Philosophy (1980; originally published in French, 1979), a survey of contemporary philosophy in France; and Alan Montefiori (ed.), Philosophy in France Today (1983), a collection of essays by French philosophers describing their own work and interests. André De Muralt, The Idea of Phenomenology: Husserlian Exemplarism (1974; originally published in French, 1958), studies the main themes in phenomenological philosophy. A useful introductory guide with an extensive bibliography is David Steward and Algis Mickunas, Exploring Phenomenology: A Guide to the Field and Its Literature (1974). Herbert Spiegelberg, The Phenomenological Movement: A Historical Introduction, 3rd rev. ed. (1982), discusses central themes in Phenomenology; and in The Context of the Phenomenological Movement (1981), he explains the background to that movement.Karl-Otto Apel, Towards a Transformation of Philosophy (1980; originally published in German, 1972), is an influential study of objectivity, subjectivity, and interpretation. Jürgen Habermas, Knowledge and Human Interests, 2nd ed. (1978; originally published in German, 1968), is a critique of Positivism. Hans-Georg Gadamer, Truth and Method (1975, reissued 1982; originally published in German, 2nd ed., 1965), gives a Heideggerian account of the interpretation of experience. Another influential contribution to recent philosophy is Emmanuel Lévinas, Totality and Infinity: An Essay on Exteriority (1969, reissued 1979; originally published in French, 1961).Works that analyze the thought of specific philosophers include: R.E. Aquila, “Two Problems of Being and Nonbeing in Sartre's Being and Nothingness,” Philosophy and Phenomenological Research, 28(2):167–186 (December 1977); Suzanne Bachelard, A Study of Husserl's “Formal and Transcendental Logic” (1968; originally published in French, 1957); John D. Caputo, The Mystical Elements in Heidegger's Thought (1978); Jacques Derrida, Edmund Husserl's “Origin of Geometry”: An Introduction (1978; originally published in French, 2nd rev. ed., 1974); Joseph P. Fell, Heidegger and Sartre (1979); Wolfgang Walter Fuchs, Phenomenology and the Metaphysics of Presence: An Essay in the Philosophy of Edmund Husserl (1976); Agnes Heller (ed.), Lukács Reappraised (1983; U.K. title, Lukács Revalued); Sang-Ki Kim, The Problem of the Contingency of the World in Husserl's Phenomenology (1977); A.M. Mirvish, “Merleau-Ponty and the Nature of Philosophy,” Philosophy and Phenomenological Research, 43(4):449–476 (June 1983); Marie-Luise Schubert Kalsi, Alexius Meinong on Objects of Higher Order and Husserl's Phenomenology (1978); and Anthony Thiselton, The Two Horizons: New Testament Hermeneutics and Philosophical Description with Special Reference to Heidegger, Bultmann, Gadamer, and Wittgenstein (1980).William Henry Walsh A.C. Grayling

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