The Relative Pronoun

A relative clause is used to form one sentence from two separate sentences(independent clause & dependent clause). The relative clause replaces one of two identical noun phrases and relates the clauses to each other.The relative pronouns are listed here.

1. That        -  things
2. Which     -  things
3. Who       -  people
4. Whom   -  people
5. Whose  -  usually people

Note : In speaking, that can be used for people, but NOT in formal written English

Remember that a sentence with a relative clause can always be reduced to two separates, so each clause must contain a verb.
                           
                                                        THAT/WHICH
That is used for explaining plural/singular things.

John bought a boat. The boat cost thirty thousand dollars.
John bought a bought that cost thirty thousand dollars.

Which is used for explaining singular things.

I have a book. The book is on the table.
I have a book which is on the table.


                                                        WHO/WHOM
Who is used when the noun phrase being replaced is in the subject position of the sentence. Whom is used when it is from the complement position.

The man is angry. The man is in this room
The man who is in this room is angry.

The men are angry. I don't like the men
The men whom i don't like are angry.

                                                         WHOSE
This relative pronoun indicates possesion.

John found a cat. The cat's leg was broken.
John found a cat whose leg was broken.