The sky is red.
The dark shape was a house.
The car looks cheap.
He is in the house.
Home is where the heart is.
In these sentences, red, a house, cheap, in the house, and where the heart is, are parts of the predicate, though they characterize the subject. Such elements are called complements because they complete the assertion of the verb; if adjectives, they are called adjective complements, or better, predicated adjectives; if nouns, they are called noun complements, or predicated nouns; if clauses or phrases, they are called complements, or predicated phrases or clauses. The verbs by means of which these complements are predicated are called copulas.
Modifiers
Almost every word in the sentence is capable of having its meaning described, restricted, emphasized, or toned down in some way—that is, any meaning in the sentence may be characterized or modified.
Heavy automobiles run smoothly.
Heavy both describes and restricts automobiles.