§ 181. A proposition may be analysed into two terms and a Copula, which is nothing more than the sign of agreement or disagreement between them.
§ 182. The two terms are called the Subject and the Predicate (§ 58).
§ 183. The Subject is that of which something is stated.
§ 184. The Predicate is that which is stated of the subject.
§ 185. Hence the subject is thought of for its own sake, and the predicate for the sake of the subject.
CHAPTER II.
Of the Copula.
§ 186. There are two kinds of copula, one for affirmative and one for negative statements.
§ 187. Materially the copula is expressed by some part of the verb 'to be,' with or without the negative, or else is wrapped up in some inflexional form of a verb.
§ 188. The material form of the copula is an accident of language, and a matter of indifference to logic. 'The kettle boils' is as logical a form of expression as 'The kettle is boiling.' For it must be remembered that the word 'is' here is a mere sign of agreement between the two terms, and conveys no notion of actual existence. We may use it indeed with equal propriety to express non-existence, as when we say 'An idol is nothing.'