PREDICATE NOMINATIVE

The predicate nominative is a noun that follows a linking verb and identifies or explains the subject of the sentence.

Example: Joe is a good policeman.

Who or what is Joe?
A policeman.
The word "is' is not an action verb but a linking verb.
The word "policeman" is a noun following a linking verb.
The word "policeman" is a predicate nominative.

Sometimes an adjective instead of a noun will follow the linking verb. (see adjectives)

Example: Joe is angry.

Who or what is Joe?
Angry.
The word "angry" follows the linking verb, but "angry" is not a noun.
There is no predicate nominative, but the word "angry" is a predicate adjective.