A relative clause is never a complete statement as it is a dependent clause. It tells us something extra about the noun that it describes. The position of the noun is immediately before the relative clause. The relative clause is introduced by a relative pronoun, which is one of the following: that, which, who, whom, whose.

 

Example: My old uncle is a bachelor.
Let us have additional information about my old uncle.
  • My old uncle is a bachelor. He showed me a photo of his new girlfriend.
We can now use a relative clause to combine the two sentences.
  • My old uncle who showed me a photo of his new girlfriend is a bachelor.
As the relative pronoun always replaces a noun or pronoun, we have used the relative pronoun who to replace the pronoun he in the last sentence above.
  • Not: My old uncle who showed me a photo of his new girlfriend he is a bachelor.

 

As mentioned above, the noun uncle is positioned immediately before the relative clause who showed me a photo of his new girlfriend which is introduced by the relative pronoun who. Uncle is a person so we use who. We use the pronouns who and that for people.
  • There is my old bachelor uncle who/that showed me a photo of his new girlfriend.

 

We do not use that for a name or a nonrestrictive (non-defining) clause. A restrictive clause is essential to the meaning of the sentence while a nonrestrictive clause is not. We can remove a nonrestrictive clause from a sentence without affecting its meaning. We can’t do that with the restrictive clause.

 
Not for a name
  • My godfather is Mr Beardson who has a long beard.
  • Not: My godfather is Mr Beardson that has a long beard.
Not for a nonrestrictive clause
  • The coconut that dropped on his head nearly killed him. (Restrictive clause)
  • Not: The coconut, which dropped on his head, nearly killed him.
  • The coconut, which I bought this morning, is used for cooking. (Nonrestrictive clause)
  • Not: The coconut, that I bought this morning, is used for cooking.

 

 

We use pronouns which or that to start a relative clause describing things.
  • I bought a pony which/that eats like a horse. (= eats a lot)
  • I have a watch which/that nowadays tells different time. (= not accurate)

 

 

We use whom for people
We use the relative pronoun whom for people when it is the object of the verb that follows. Even though whom is the object of the clause, it comes at the beginning of the relative clause just like the other relative pronouns which are subjects of the clause.
  • The deceased was a close friend whom I have been thinking of for a long time.

 

 

We often omit a relative pronoun, especially in speech when it is the object of the relative clause.
  • The one thousand dollars, which he won in a lottery, lasted only a week.
    The one thousand dollars he won in a lottery lasted only a week.
  • He is my only friend whom I have fought with.
    He is my only friend I have fought with.
  • The pet rabbit that I bought yesterday died this morning.
    The pet rabbit I bought yesterday died this morning.
But we cannot omit a relative pronoun when it is the subject of the relative clause.
  • The tooth that caused him toothache the whole night has been extracted.
    Not: The tooth caused him toothache the whole night has been extracted.
  • The fire, which burnt down the row of wooden houses, was started from a cigarette butt.
    Not: The fire burnt down the row of wooden houses was started from a cigarette butt.

 

 

Prepositions used in relative clauses
Prepositions appear either at the beginning or at the end of relative clauses.
  • This is the house, for which he paid a million dollars.
    This is the house, which he paid a million dollars for.
  • That is the roller coaster, on which we rode.
    That is the roller coaster, which we rode on.
  • In that cottage lived my uncle with whom I stayed for a year.
    In that cottage lived my uncle whom I stayed with for a year
When the preposition is at the end of a relative clause, we can replace which and whom with that.
  • This is the house that he paid a million dollars for.
  • That is the roller coaster that we rode on.
  • In that cottage lived my uncle that I stayed with for a year.

 

 

So far, we have been talking about a relative clause describing a noun. We can also use a relative clause to describe the whole main clause.
  • Look at the two old men fighting, which is very childish.
  • Dad refused to lend me his car, which is very disappointing.