Relative pronouns begin a subordinate clause. Examples are: that, which, who and whom.
Who, which and that can be the subjects of the verbs in relative clauses. Who refers to people and which to things; that can refer to both people and things.
- The boy who stole the watch was punished. (NOT The boy which stole ...)
- It is a book which will interest children of all ages. (NOT It is a book who will ...)
- The people that/who live next door keep having all-night parties.
- These are the keys that open the front and back door.
Who, whom, which and that can also be used as the objects of verbs in relative clauses. Who is informal as an object; in a more formal style whom is used.
- He is married to somebody who I really don't like. (Informal)
- He is married to somebody whom I really don't like. (Formal)
Relative pronouns as conjunctions
Relative pronouns serve two purposes: they act as subjects or objects inside their relative clauses, and at the same time they connect relative clauses to nouns or pronouns in other clauses - rather like conjunctions.
- I have found the car keys. You were looking for them.
- I have found the car keys which you were looking for.
- This is Mr Peter. You met him last year.
- This is Mr Peter whom you met last year.
- Here is an article. It might interest you.
- Here is an article which might interest you.