WHAT IS A RELATIVE CLAUSE?

A relative clause adds information about one of the nouns in the main clause. The relative clause comes immediately after the noun it relates to:

Mr Danielson, who lived in the big rambling house next to our Store, was very tall and broad.

His big many-windowed house had a porch that clung to its sides.

RELATIVE PRONOUNS: who, whom, which, that, whose

A relative pronoun goes at the beginning of a relative clause.

WHO, WHOM
Who and whom are used for people. Whom is only used when the relative pronoun is the object of the relative clause; nowadays in informal English it is usually replaced by who or that:

He was a simple man who sold patent medicine.
The lawyer whom you requested is unavailable.

WHICH
Which is used for things:

I enjoyed the book which you lent me.

THAT
That may often be used instead of who, whom or which:

I enjoyed the book that you lent me.
The lawyer that you requested is unavailable.

WHOSE
You use whose in a relative clause to show who something belongs to. It may be used for people or things:

Mrs Foster, whose garden I enjoyed playing in, never spoke to me.
That's the house whose garden is open to the public.

RELATIVE PRONOUNS: Subject / Object

The relative pronoun may be the subject or the object of the relative clause. Is who the subject or the object in these sentences?

Mr Ronald was a neighbour WHO (object) Maria enjoyed watching.
He was a simple man WHO (subject) sold patent medicine.

PLEASE, REMEMBER:
When the relative pronoun is the object of the clause it may be left out:

Mr Ronald was a neighbour Maria enjoyed watching.

TYPES OF RELATIVE CLAUSE

There are two main types of relative clause:

The information in a defining relative clause is essential to the meaning of the main clause. If the defining relative clause is taken away, the meaning of the main clause is not clear:

Herbert was the only Norgewian I knew who wore matching pants and jackets.

Please, note that in the example given above there are two defining relative clauses: I knew and who wore matching pants and jackets. The meaning of the main clause is not clear if either of these clauses is taken away from the sentence.

Also note these differences between formal and informal English:

INFORMAL ENGLISH: Uncle Ted was a person who I enjoyed talking to.
FORMAL ENGLISH: Uncle Ted was a person to whom I enjoyed talking.

PLEASE, REMEMBER:
In defining relative clauses:
1) You may leave out the relative pronoun if it is the object of the relative clause.
2) You should not use commas to separate the relative clause from the rest of the sentence.

The information in a non-defining relative clause is extra. If the non-defining relative clause is taken away, the meaning of the main clause is still clear:

Mr Danielson, who lived in the big rambling house next to our Store, was very tall and broad.

PLEASE, REMEMBER:
In non-defining relative clauses:
1) You must not leave out the relative pronoun, even if it is the object of the clause.
2) You must not use the relative pronoun 'that'.
3) You must use a comma or commas to separate the clause from the rest of the sentence.