The predicative is an element of the predicate of a sentence which supplements the subject or object by means of the verb. Predicatives may be nominal or adjectival. A predicate nominative is a noun or pronoun that follows a linking verb and renames the subject.

He seems stupid. (adjectival predicative of the subject)

Bob is a postman. (nominal predicative of the subject)

We painted the door white. (adjectival predicative of the object)

They elected him president. (nominal predicative of the object)

Though they are sometimes termed complements, object predicatives are often able to be omitted leaving a well-formed sentence.

grammar