First-order predicate

In mathematical logic, a first-order predicate is a predicate that takes only individual(s) constants or variables as argument(s).{{citation|title=A Dictionary of Philosophy: Revised Second Edition|first=Antony|last=Flew|publisher=Macmillan|year=1984|isbn=9780312209230|page=147|url=https://books.google.com/books?id=MmJHVU9Rv3YC&pg=PA147}}. Compare second-order predicate and higher-order predicate.

This is not to be confused with a one-place predicate or monad, which is a predicate that takes only one argument. For example, the expression "is a planet" is a one-place predicate, while the expression "is father of" is a two-place predicate.