Predicate nominatives in English grammar are nouns, pronouns, noun phrases, and noun clauses that perform the grammatical function of subject complement. Subject complements are words, phrases, and clauses that follow a copular, or linking, verb and refer back to modify, describe, or complete the grammatical subject of the clause.
Predicate nominative is a grammatical function.
The grammatical forms that can function as the predicate nominative in English grammar are noun phrases and noun clauses.
The term predicate noun is also used for noun phrases that function as subject complements.
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Hopper, Paul J. 1999. A short course in grammar. New York: W. W. Norton & Company.
Huddleston, Rodney. 1984. Introduction to the grammar of English. Cambridge: Cambridge University Press.