syllogism

/sil"euh jiz'euhm/, n.

1. Logic. an argument the conclusion of which is supported by two premises, of which one (major premise) contains the term (major term) that is the predicate of the conclusion, and the other (minor premise) contains the term (minor term) that is the subject of the conclusion; common to both premises is a term (middle term) that is excluded from the conclusion. A typical form is "All A is C; all B is A; therefore all B is C."

2. deductive reasoning.

3. an extremely subtle, sophisticated, or deceptive argument.

[1350-1400; < L syllogismus < Gk syllogismós, equiv. to syllog- (see SYLLOGIZE) + -ismos -ISM; r. ME silogime < OF < L, as above]

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Form of argument that, in its most commonly discussed instances, has two categorical propositions as premises and one categorical proposition as conclusion.

An example of a syllogism is the following argument: Every human is mortal (every M is P); every philosopher is human (every S is M); therefore, every philosopher is mortal (every S is P). Such arguments have exactly three terms (human, philosopher, mortal). Here, the argument is composed of three categorical (as opposed to hypothetical) propositions, it is therefore a categorical syllogism. In a categorical syllogism, the term that occurs in both premises but not in the conclusion (human) is the middle term; the predicate term in the conclusion is called the major term, the subject the minor term. The pattern in which the terms S, M, and P (minor, middle, major) are arranged is called the figure of the syllogism. In this example, the syllogism is in the first figure, since the major term appears as predicate in the first premise and the minor term as subject of the second.

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▪ logic

      in logic, a valid deductive argument having two premises and a conclusion. The traditional type is the categorical syllogism in which both premises and the conclusion are simple declarative statements that are constructed using only three simple terms between them, each term appearing twice (as a subject and as a predicate): “All men are mortal; no gods are mortal; therefore no men are gods.” The argument in such syllogisms is valid by virtue of the fact that it would not be possible to assert the premises and to deny the conclusion without contradicting oneself.

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