In dated or non-theoretical grammatical terminology, a subject complement is a predicative expression that follows a linking verb (copula) and that complements the subject of a clause by either renaming or describing it. It completes the meaning of the subject. In the former case, a renaming noun phrase such as a noun or pronoun is called a predicative nominal. An adjective following the copula and describing the subject is called a predicative adjective. In either case the predicative complement in effect mirrors the subject. Subject complements are used with a small class of verbs called linking verbs or copulas, of which be is the most common. Since linking verbs are intransitive, subject complements are not affected by any action of the verb. Subject complements are typically neither clause arguments nor adjuncts. A predicative complement can be either a subject complement or an object complement.
A subject complement does not determine the verb. When there is a difference between the number, the verb agrees with the subject.