Relative clauses

We use them to combine two sentences, avoiding repetitions, when the second sentence refers to an element of the first sentence. Here it's an example:

-The book is about History. The book is on the table

We don't want to repeat “book” and we prefer to have only one sentece, so we use a relative pronoun:

- The book which is on the table is about History.

In this example, “which” has the function of “the book”, so we don't repeat it.

To make relative clauses we use relative pronouns:

Pronoun	Refers to	Example
who	people	This is the man who helped me fix the bike.
which	things	The dog which bit me was a pitbull.
that*	people/things	The computer that I had doesn't work anymore.
whose	possesion of people/things	Peter, whose mother is a teacher, want to become a doctor.
when	times	I didn't sleep last night, when I was at my friend's house.
where	places	That is the restaurant, where we ate that tasty fish.
why	reason	That's the reason why I couldn't come yesterday.

* “That” can replace “who” and “which”

This is the man that helped me fix the bike.

The dog that bit me was a pitbull.

There are two types of relative clauses:

- Defining clauses: they add important information to the sentece. They never go between commas.

He has been working in a shop which sells souvenirs.

- Non defining clauses: they don't add essential information. They go between commas. In this type of relative clauses “that” can never be used.

My sister, who is 26 years old, has bought a new car.

Defining vs non-definig clauses

The elephants, who are big, don't live in Spain.

The elephants who are big don't live in Spain.

Let's pay attention to this two sentences, because commas aren't their only difference. The first sentence (non-defining) tells us that the elephants are big and that they don't live in Spain. However, the second one (defining) says that big elephants don't live in Spain, but perhaps small elephants could live there.