Relative clauses give us extra information about something/someone or identify which particular thing/person we are talking about. They are often introduced by the following words.
which (for things and animals)
Did you see the film which was on TV last night?
who (for people, and animals when we want to give them a personality)
Tom Davies, who is appearing in concert in Reading this week, is with me in the studio.
when (for times)
Do you remember the day when we met?
where (for places)
This is the place where they filmed Citizen Kane.
why (for reasons)
That's the reason why he's so popular.
whose (for possession)
My next guest on the show is John Travolta, whose career goes back to the early seventies.
whom (for people as the object of the relative clause)
Is that the man whom we saw at the cinema yesterday?
Whom is quite formal. It is natural in informal English to use who instead of whom, even when it is the object of the relative clause. After a preposition, however, we always use whom. Informally, we usually put the preposition at the end of the clause and use who.
✓ Is that the man who we saw at the cinema yesterday?
✓ Charlie Chaplin was a comic genius to whom all comedians owe a great deal.
✓ Charlie Chaplin was a comic genius who all comedians owe a great deal to.
Non-defining relative clauses
Non-defining relative clauses simply give us more information about something/someone. The sentence makes complete sense without the relative clause.
Ray Watson, who starred in Bandits, is considering making a film based on the life of Einstein.
• Non-defining relative clauses are separated from the rest of the sentence by commas.
✓ Megamonsters, which was filmed in New York, is a very disappointing film.
• We cannot leave out the word which introduces the relative clause and we cannot use the word that instead.
X Megamonsters, was filmed in New York, is a very disappointing film. X Megamonsters, that was filmed-in New York, is a very disappointing film.
• Which can refer back to the whole of the sentence.
✓ We finally got tickets for the concert, which was very lucky. (It doesn't mean the concert was lucky. It means getting tickets for the concert was lucky.)
Defining relative clauses
Defining relative clauses tell us which one of a group of things/people we are talking about.
The sentence doesn't usually make complete sense without the relative clause.
The book which I've read was the best of all.
The one who is wearing a blue shirt is Justin Timberlake, isn't it?
• Defining relative clauses are not separated from the rest of the sentence by commas.
✓ This is the DVD which I told you about the other day.
• We can also use that to introduce the relative clause.
✓ This is the DVD that I told you about the other day.
• We can often leave out the word which introduces the relative clause when it is the object of the clause.
✓ This is the DVD I told you about the other day.
• Notice that we do not need a preposition when we use where or when.
✓ The theatre where I first acted is somewhere around here.
X The theatre where I first acted in is somewhere around here.
✓ Do you know the year when the first western was made?