Relative pronouns introduce a sentence (relative clause) that gives us additional information about the person or thing we are talking about. They are also used to determine exactly the person or thing we are referring to.

The boy who has a cap is my brother.

This is the contract which has to be signed.

2. What are relative clauses?

A relative clause is a subordinate sentence introduced by a relative pronoun (who, which...). There are two types of relative clauses:

DEFINING

They are subordinate sentences that give us essential information to identify who or what we are referring to.

NON-DEFINING

Son oraciones subordinadas que nos dan información adicional sobre la persona o cosa a la que nos referimos. Esta información no es necesaria para identificar al sujeto de la oración. Está separada por comas.

The girl who lives next door is always making noise.

In this example, the defining relative clause is introduced by the relative pronoun who. In this case, the information introduced is vital to know that the person who makes noise is the girl who lives next door and not another one.

NON-DEFINING

They are subordinate sentences that give us additional information about the person or thing we are referring to. This information is not necessary to identify the subject of the sentence. It is separated by commas.

Peter, who lives next door, plays the guitar.

In this example, the non-defining relative clause is also introduced by the relative pronoun who. In this case, the information is additional, we don't need it to identify who we are talking about because we know it's Peter.

3. The different relative pronouns

There are different relative pronouns we can use to introduce both defining and non-defining relative clauses:

WHO

It is used when we are referring to people.

Those who want to take part in the school play raise your hands.

Michelangelo, who was both a painter and a sculptor, also write poems.

WHICH

It is used when we are referring to things and animals.

The cottage which we rented was lovely.

This clock, which is from 1886, is worth $4,300.

We can replace who and which with the particle that, but only in defining relative clauses.

Defining	NoN-defining
The woman who/that is giving the lecture is from Sweden.	That woman, who/~~that~~ is from Sweden, is giving an interesting lecture.
The letter which/that is on the table is for Adam.	The letter, which/~~that~~ is for Adam, is on the table.

WHOSE

It is used when we are referring to a possession.

The man whose dog is a dalmatian is my teacher.

This place, whose beach is gorgeous, is in Milos.
WHERE

It is used when we are referring to a place.

The box where the old toys are is in the garage.

That library, where I used to go after school, is going to be restored.
WHEN

It is used when we are referring to a period of time.

I still remember the day when you proposed.

The year 2010, when I went to study abroad, was the best of my life.

4. Omission of relative pronouns

Relative pronouns can be omitted in spoken English or in informal writing when they are not the subject of the sentence, but the object.

CAN'T BE OMITTED	CAN BE OMITTED
The boy kissed Laura. He was handsome.	Laura kissed a boy. He was handsome.
~~The boy kissed Laura was handsome~~	The boy who Laura kissed was handsome.
The boy who kissed Laura was handsome.	The boy (who) Laura kissed was handsome.

In the first case who cannot be omitted because the boy is the subject of the sentence, since he is the one who does the action. In the second case, we can omit the who because the boy is the object of the sentence, that is, he is not the one who does the action.

The relative pronoun can only be omitted with defining relative clauses.

The socks (which/that) they are wearing are super cute.

This is the girl (who/that) I met at the summer camp.

Remember!

Relative pronouns introduce a relative clause, which gives or adds information about the person or thing being talked about. They can introduce either defining or non-defining relative clauses.

Relative pronouns	Use	Examples
Who / that	people	The lawyer who/that is handling the case is very good.
Which / that	things	The sweater which/that I'm wearing is handmade.
Whose	possessions	That's the woman whose photos are on display at the Dyson Gallery.
Where	places	The theatre where we performed was very old.
When	time	Do you remember the night when the accident happened?

Remember that the relative pronoun can be omitted in defining relative clauses when they act as an object.