Syllogism

Webster's Dictionary

(n.) The regular logical form of every argument, consisting of three propositions, of which the first two are called the premises, and the last, the conclusion. The conclusion necessarily follows from the premises; so that, if these are true, the conclusion must be true, and the argument amounts to demonstration

The Nuttall Encyclopedia

An argument consisting of three propositions, of which two are called premises, major and minor, and the one that necessarily follows from them the conclusion.