Complement means, “to complete,” and complementation has to do with “completing the meaning of a verb. Many times, verbs in English sentences are completed by constructions that are not just modifiers. A structure of complementation has two immediate constituents: a verbal element and a complement. The verbal element may be a simple verb, or it may be any structure that has a verb in key position. Thus, it may be a verb-phrase, an infinitive, a structure of modification with verb as head, or structure of coordination whose components are any of these.
In order to identify and describe different types of complements, we must first note that the verbs, which are at the core of the various types of verbal element, may be divided into three main groups: linking (or copulative) verb, intransitive verb and transitive verb (Nelson and McDavid, 1985: 343). In addition, Thomas (1993:37) divides verb into six classes: Transitive Verb, Intransitive Verb, Ditransitive Verb, Intensive, Complex-Transitive Verb, and Prepositional Verb.Nelson and McDavid (1985: 346) explained that since intransitive verbs and prepositional verb have no complement, they do not appear in structures of complementation. Each of the other two types has its own kinds of complement. Complements appearing with linking verb are called Subjective Complement; Complements appearing with Transitive Verb are called Objects.