In grammar, a complement is a word, phrase or clause that is necessary to complete the meaning of a given expression. Complements are often also arguments (expressions that help complete the meaning of a predicate.
There are indicative as well as non-indicative complements in languages. Non-indicative complements follow the appropriate complementizers. Indicative complements do not follow complementizers but instead are included with special markers and clauses.
In many non-theoretical grammars, the terms subject complement and object complement are employed to denote the predicative expressions that serve to assign a property to a subject or an object:
- Ryan is upset. – Predicative adjective as subject complement
- Rachelle is the boss. – Predicative nominal as subject complement
- That made Michael lazy. – Predicative adjective as object complement
- We call Rachelle the boss. – Predicative nominal as object complement
The Cambridge Grammar of the English Language assigns the term "predicative complement" to both uses and shifts the terminological distinction to the verb:
- Ed seemed quite competent: — complex-intransitive verb + predicative complement
- She considered Ed quite competent : — complex-transitive verb + predicative complement
In many modern grammars, the object argument of a verbal predicate is called a complement. In fact, this use of the term is the one that currently dominates in linguistics. A main aspect of this understanding of complements is that the subject is usually not a complement of the predicate:
- He *wiped the counter*. – the counter is the object complement of the verb wiped.
- She *scoured the tub*. – the tub is the object complement of the verb scoured.