Relative clauses - defining, non-defining.
Non-defining (or non-identifying) relative clauses.
Let us imagine two very different planets in the solar system. Firstly, our planet Earth which has just ONE moon.
We can talk about our moon like this:
The moon, which goes around Earth, is covered in rocks.
Our moon, which has no atmosphere, is a cold and lonely place.
The surface of the moon, which is not really yellow but grey, has no rivers or streams.
Each sentence uses a relative pronoun (which) and a clause between commas which gives us additional information about our single moon. There is only one moon so the clause does not identify or define which moon - we know there is only one. We call these clauses non-defining relative clauses.
Defining (or identifying) relative clauses.
Now let us take a spaceship to Mars. This red planet has TWO moons.
The moon which/that is closer to Mars is also the larger of the two.
The moon which/that is just 22.7 km in diameter is called Phobos.
The moon which/that is further away from Mars (called Deimos) takes over 30 hours to orbit the mother planet.
The moon which/that is closer to Mars (Phobos) orbits the planet twice a day. Phobos crosses the sky in only 4 hours.
When we talk about one of the moons, we must identify or define which moon we are talking about. We do this with relative clauses with no commas. We use which as a relative pronoun or that in more informal or spoken English. We call these clauses defining relative clauses.
More examples of non-defining relative clauses.
When talking about things or concepts, we use which. When we talk about people, we use who in non-defining relative clauses:
My English dictionary, which I lent to Pedro last week, now has pages missing.
I gave John an Aspirin, which he refused to take, because he said he had a bad headache.
We like the project, which is new and original, and have plans to develop it.
The builders, who are extremely slow in their work, are costing us a lot of money.
This is Mary Smith, who has been working here for six years.
The local police, who have been searching for the body for weeks, are very confused.
Note that in all the sentences above, the relative clauses separated by commas are just extra information. We can take out the relative clause and the sentence still makes sense:
My English dictionary now has pages missing.
The builders are costing us a lot of money.
Non-defining clauses are more common in formal spoken speech and written English because the sentences are long and very controlled.
More examples of defining relative clauses.
When we talk about things or concepts, we can use which or that. When we talk about people, we use who or that in defining relative clauses:
Where's the taxi which/that is taking us to the theatre?
This is the project which/that we have been considering.
That's the shop-assistant who/that sold me these trousers.
There are a lot of people in this area who/that are very wealthy.
Which and who and not that is often preferred in more formal speech and written English:
The investment programme which was adopted last year is proving successful.
Staff members who have been with the company for over ten years will receive a bonus.
Omission of that in defining relative clauses.
In defining relative clauses only, when a relative pronoun refers to the object of the sentence, we can omit the pronoun from the sentence. This happens especially in conversational English:
I can't find the postcards (that) I bought yesterday.
Nothing (that) you say will change my mind.
He's a person (that) I'd like to meet.
Everybody (that) we spoke to was very kind.
Note that the antecedent (underlined) is the object or complement of the sentence.
Exercises on relative clauses...
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