Universa Philosophia

The subject is that of which we say or predicate something, as in the proposition Peter is white: Peter is the subject, because of him it is said and predicated that he is white. The predicate, in turn, is the thing that is said or predicated of another; thus white is predicated and said of Peter in that proposition. Subject is so called from subiicio, that is, “it is thrown beneath another.” For just as, among physical things, Peter is a subject because he lies beneath accidents, while the accidents are in Peter, so logically the subject is what underlies predication, which places the predicate in it. The predicate, however, is so called because it is the thing predicated. The union is so called because it unites or joins the subject to the predicate. For it signifies that the subject and predicate are the same, which is to unite them. In a negative proposition, however, it does not unite but separates the predicate from the subject and denies that they are the same, as in Peter is not a stone.