Relative clause

A relative clause is a dependent clause introduced by a relative pronoun (who, whom, whose, which or that) that modifies a noun, either to identify which one is meant or to add detail about one already identified.

The man who called yesterday left no number. The bold part is a relative clause: it has its own verb, and its job is to describe the noun in front of it.

The relative words

• who, whom for people: the teacher who marked it, the friend whom I trusted.
• whose for possession: the neighbour whose dog barks all night.
• which for things: the car, which had no brakes.
• that for people or things in identifying clauses: the key that opens the shed.
• where and when can do the same job for places and times: the town where she was born.

Restrictive and non-restrictive

There are two kinds, and confusing them is one of the few punctuation errors that changes the facts.

Restrictive: no commas. The clause identifies which one you mean, so the sentence loses its sense without it.

The drafts that she had annotated went back in the folder.

Only the annotated ones went back. The clause is a bound modifier: it cannot be lifted out.

Non-restrictive: commas. The noun is already identified, and the clause adds something extra.

The drafts, which she had annotated, went back in the folder.

All of them went back, and by the way they were annotated. The clause is a free modifier, removable without damage.

The usual guidance in American usage is that for restrictive and which for non-restrictive; British usage allows which in both, but the commas still do the work. If you can drop the clause and the sentence still means what you intended, use the commas; if you cannot, leave them out.

Common mistakes

• Commas on an identifying clause. My brother, who lives in Leeds, is a nurse tells the reader you have one brother. If you have two, the clause is saying which one, so drop the commas.
• A clause parked far from its noun. I bought the lamp from the shop that was broken. Was the shop broken? Move the clause next to the noun it describes.
• Clause after clause. The man who owned the dog that bit the boy who... Break it up.

A non-restrictive relative clause and an appositive phrase do almost the same job, and the appositive is usually shorter: the drafts, all of them annotated, rather than the drafts, which she had annotated.

Frequently asked questions

What is a relative clause?

A relative clause is a clause that describes a noun and usually starts with who, whom, whose, which or that. In 'the man who called', the clause 'who called' tells you which man.

When do I use that and when do I use which?

In American usage, 'that' introduces a clause that identifies the noun, with no commas, and 'which' introduces extra information set off by commas. British usage also allows 'which' without commas, so the commas are the real signal.

Can you leave out the relative pronoun?

Often, yes, when it is the object of the clause: 'the book that I lent you' can become 'the book I lent you'. You cannot drop it when it is the subject: 'the man who called' needs 'who'.