Of Expression and Interpretation

Summary

A Proposition is a sentence which either affirms or denies, as, All men are mortal, No creature is independent.

A Proposition has necessarily two terms, as men, mortal; the former of which, or the one spoken of, is called the subject; the latter, or that which is affirmed or denied of the subject, the predicate. These are connected together by the copula is, or is not, or by some other modification of the substantive verb.

The substantive verb is the only verb recognised in Logic ; all others are resolvable by means of the verb to be and a participle or adjective, e.g. “ The Romans conquered”; the word conquered is both copula and predicate, being equivalent to “were (copula) victorious” (predicate).

A Proposition must either be affirmative or negative, and must be also either universal or particular. Thus we reckon in all, four kinds of pure categorical Propositions.

1st. Universal-affirmative, usually represented by A,

Ex. All Xs are Ys.

2nd. Universal-negative, usually represented by E,

Ex. No Xs are Ys.

3rd. Particular-affirmative, usually represented by I,

Ex. Some Xs are Ys.

4th. Particular-negative, usually represented by O,

Ex. Some Xs are not Ys.