The best example of the copula in English, and many other languages, is the verb
to be, which most often serves to link the subject of the sentence with the predicate -- a part of the sentence which modifies the subject. Some examples of this use of
to be include:
Can anything ever be enough? The house is on top of the hill. Jets are fast.
Notice how in each of these sentences, the verb
to be is not being used in the literal verbal sense, meaning 'to exist', but is rather taking the second part of the sentence -- the predicate -- and using it to modify the first part.
Copula Verb 
Linear Mode
