A predicate thought of as an open sentence that requires n variables to be either bound or substituted by a referring expression to make a closed sentence. Thus ‘x is the daughter of y’ is a two-place predicate, that can be turned into a sentence either by substitution of names: Mary is the daughter of Emma; or by a name and a quantification binding one variable: (∃x) Mary is the daughter of x; or by binding both variables: (∃x)(∃y) x is the daughter of y.