A form used in
logical argument. A
categorical syllogism consists of two
premises which contain a
common idea, one being
universal. From these, a
conclusion can be drawn.
One premise relates the major term (P) with the middle term (M). The other relates the minor term (S) and the middle term. The conclusion relates the minor and major terms. The syllogism may take any of the following forms:
Major term: M--P P--M M--P P--M
Minor term: S--M S--M M--S M--S
Conclusion: S--P S--P S--P S--P
Note that the
conclusion cannot contain the middle term. In addition, the middle term must be a
universal at least once, and the major and minor terms may not be used as universals in the conclusion if they were
particulars in the premises. At least one premise must be
affirmative; if one is
negative, the conclusion must be negative, and if both are affirmative the conclusion must be as well. In addition, at least one must be universal; the conclusion may be universal only if both premises are. If any of these rules are violates, a
logical fallacy results.