In grammar the term complement is sometimes used with different meanings. The core meaning of complement is for a word, phrase or clause which is necessary in a sentence to complete its meaning. We find complements which function as a sentence element (i.e. of equal status to subjects and objects) and complements which exist within sentence elements.

Complements which are sentence elements

subject complement

A subject complement tells more about the subject by means of the verb. In the examples below the sentence elements are (SUBJECT + VERB + COMPLEMENT)

Mr Jenner is a management consultant. (a predicative nominal)

She looks ill. (a predicative adjective)

object complement

An object complement tells us more about the object by means of the verb. In the examples below the sentence elements are (SUBJECT + VERB + OBJECT + COMPLEMENT). Object complements can often be removed leaving a well-formed sentence, thus the use of the term complement is slightly illogical.

We elected him chairman. (a predicative nominal)

We painted the house white. (a predicative adjective)

adverbial complement

Adverbials, central to the meaning of a sentence, are usually an adjunct (i.e. they can be removed and a well-formed sentence remains). If, however, an adverbial is a necessary sentence element then it is correctly referred to as a complement. The structure of the sentence below is (SUBJECT + VERB + ADVERBIAL COMPLEMENT)

John is in the garden.

N.B. Some grammarians like to refer to the objects of the sentence as complements of the predicate. This usage while possible is confusing.