A predicate is any expression that is capable of connecting with one or more singular terms to make a sentence. A predicate expresses a condition that the entities referred to may satisfy, in which case the resulting sentence will be true. For this reason a predicate may be thought of as a function from things to sentences or even to truth-values. Although modern logic makes a sharp distinction between predicates and terms that stand for things, traditional logic did not. In the theory of the syllogism the subject and predicate terms are thought of as grammatically interchangeable, as ‘All A is B, all B is C, so all A is C’, where the term B is a predicate on its first occurrence, but thought of as a subject on the next. The modern treatment denies that such a form is subject-predicate at all, but sees it as a quantification, involving two predicates: (∀x)Ax→Bx. The letters A, B…, or more usually F, G…, are predicate letters, standing where predicates would stand in sentences when we are considering the logical form of arguments.