Socrates is the subject in the sentence Socrates is mortal and is mortal is the predicate. In predicate logic, a predicate designates a property or a relation. P in P(a) and R in R(b,c) are called predicates. P in P(a) assigns a property to a and R in R(b,c) designates a relation between b and c. The expressions a, b and c are called the arguments of the predicates P and R.
- Gamut, L.T.F. 1991. Logic, language, and meaning, Univ. of Chicago Press, Chicago.