49. The Syllogism. Terminology. -- Reasoning, then, consists in comparing the subject and predicate of a not evident judgment, which is to be the conclusion, with a middle term to see whether, objectively, the one implies the other or excludes it. Its complete and typical expression is the syllogism. "The syllogism", says Aristotle, "is a discourse in which, certain things being laid down, another thing follows necessarily, simply because those things are laid down."^{1}

When the reasoning faculty declares that the predicate agrees objectively with the subject, the conclusion is affirmative; when it sees that one of the two terms agrees with the middle term while the other does not, the conclusion is negative.

The two terms of the conclusion are called extreme terms or extremes, in opposition to the middle term (medius terminus) with which they are both compared.

The predicate is called the great extreme; the subject, the small extreme.

The two propositions from which the conclusion is drawn are called premises (praemittuntur conclusioni); together they form the antecedent. The premises are those things which, according to Aristotle, once laid down or supposed, draw the conclusion after them.

The consequent is the conclusion. The proposition first in order to be enunciated is often called the major; the second, the minor. But more exactly, the proposition in which the great extreme is put with the middle term is called the major (Major, propositio); that in which the small extreme is compared with the middle term, the minor (Minor, assumpta).

The premises and the conclusion, the antecedent and the consequent, constitute the matter of the syllogism. The form lies in the bond between the antecedent and the consequent; it is condensed in the particle therefore, which expresses the consequence (consequentia, consecutio) of the syllogism.

To study the nature of reasoning is to investigate what causes that "certain things being laid down, another thing must necessarily follow simply because those things are laid down."

{1} Prior Anal., 1, 1.