Complements are closely related to preceding constituents in the clause:

A subject complement usually follows a copula verb; it refers to the subject:

She is the new president.

\_______/

An object complement follows the direct object, which it refers to.

They have made her president.

\__/

Both types of complement are normally realised by noun phrases or adjective phrases.

NB: Although the complement and its referent are in mutual correspondence (and the copula verb may even suggest a relationship of equality) the two of them must not be inverted. This linear progression is so rigid as it is closely related to the governing principles of information structure in English.