The given definition follows the usage of "predicate" in logic. One way of forming predicates is to take a statement and replace one or more subject terms - normally terms that are like common or proper names - by variables or placeholders. An example is "x1 loves x2" or "_ loves _" from "Romeo loves Juliet".

The number of variables or placeholders in a predicate is called its arity or adity. Thus "x1 loves x2" is a two-place or binary predicate; "x1 is a man" is a one-place or unary predicate; and "x1 is between x2 and x3" is a three-place or triadic predicate.

In logic, predicates with two or more places stand for relations.