The parts of the proposition that refer to classes are called the terms of the proposition, and there are two terms: the subject and the predicate, symbolized by S and P. Subjects and predicates are not always single words.

In addition to the subject and predicate, there is a second component of categorical propositions, indicated by the words "is" or "are." This is called the copula because it links subject and predicate.

In terms of classes, we can make both the affirmative statement that S is included in P and the negative statement that S is excluded from P. The affirmative or negative character of a proposition is called its quality.

The fourth component of a proposition is called its quantity. A proposition with the form "All S are P" is universal, as is the proposition "No S are P." A proposition with the form "Some S are P" is particular. A proposition with the form "Some S are not P" is also particular.