In grammar a complement – not to be confused with a compliment! – is a way to provide more information about the subject or the object of a sentence.
He is gorgeous!
Did you like the present she gave you?
A complement completes an idea, whether this is expressed with a phrase, a clause or a word.
When the complement refers to the subject of a sentence we talk about subject complement. When it refers to the object we talk about object complement.
A subject complement completes the subject by giving it a quality or a name.
This meat smells funny when you cook it.
Funny gives a quality to the subject (the meat).
Her mother became the center of all the village gossip.
the center of all the village gossip gives a name to the subject (her mother).
When a complement gives a subject a quality, it is usually an adjective, or an adjectival phrase.
I am exhausted
The poor little boy broke his leg on his birthday.
When a complement gives a subject a name, it is usually a noun, a noun phrase or a noun clause.
Even an innocent pair of sunglasses can become a weapon.
This is not a car! It is a ridiculously old, smelly contraption.
The question is how do we get out of this mess now.
Subject complements usually follow linking verbs like: be, seem, look, become, appear, feel, grow, smell, taste, sound etc.
She is very young.
Her homemade cookies soon became popular.
That dog smells awful.
Object complements follow the direct object. In general, verbs which have to do with perceiving, judging, or changing something can cause their direct objects to take an object complement.
They have painted their kitchen green.
The witness called him a liar.
The police caught him driving fast.
Phrases in English Grammar – what is considered a phrase and how many types there are
Clauses in English Grammar – all about clauses – formation, types, examples
Adjectival Phrases in English – what they are and how to identify them
Noun Phrases in English Grammar – all about another common type of phrase