Defining & non-defining relative clauses

http://learnenglish.britishcouncil.org/en/grammar-reference/relative-clauses-non-defining-relative-clauses

Relative clauses - non-defining relative clauses

Relative clauses add extra information to a sentence by defining a noun. They are usually divided into two types –defining relative clauses and non-defining relative clauses.

Non-defining relative clauses

Look at this sentence.

• My grandfather, who is 87, goes swimming every day.

‘who is 87’ is a non-defining relative clause. It adds extra information to the sentence. If we take the clause out of the sentence, the sentence still has the same meaning.

Look at some more examples.

• The film, which stars Tom Carter, is released on Friday.
• My eldest son, whose work takes him all over the world, is in Hong Kong at the moment.
• The car, which can reach speeds of over 300km/ph, costs over $500,000.

Non-defining relative clauses add extra information to sentences.

Defining or non-defining?

Remember that defining relative clauses are used to add important information. The sentence would have a different meaning without the defining relative clause.

• I’m going to wear the skirt that I bought in London. The defining relative clause tells us which skirt.
• The skirt, which is a lovely dark blue colour, only cost £10. The non-defining relative clause doesn’t tell us which skirt – it gives us more information about the skirt.

Non-defining relative clauses can use most relative pronouns (which, whose etc,) but they CAN’T use ‘that’ and the relative pronoun can never be omitted.

• The film, that stars Tom Carter, is released on Friday.

Non-defining relative clauses are more often used in written English than in spoken English. You can tell that a clause is non-defining because it is separated by commas at each end of the clause.