Grammar notes: relative clauses
A relative clause is a part of a sentence beginning with a relative pronoun (although this pronoun can be omitted in certain cases). For example:
The company where I worked is called International Enterprises Plc.
The man who went into the baker's bought a loaf of bread.
My sister, who lives near London, is coming to visit me soon.
Basic relative pronouns
The relative pronoun you use depends on the thing you're talking about. Generally speaking, the most basic ones are these:
Who, which and that cannot be used indiscriminately. That can only be used in defining relative clauses.
Trickier relative pronouns
Four relative pronouns often seem to confuse people, but they're easy to use too.
This can be used to refer to the whole part of the sentence that went before. Usually a pronoun refers to a noun, but this refers to more. For example:
I've broken my leg, which means I can't walk.
I've still got some money left, which is surprising.
This is hardly ever used in spoken English, and not often in written English. It sounds very formal to most people. If you're going to use it at all, then only use it after prepositions. Even so, there's usually another less formal way to say the same thing. For example:
The woman to whom he was talking is his sister.
The woman that he was talking to is his sister.
This is used to show possession. It means basically 'of who(m)'. It can always be used for people and animals, but also for things, though this sometimes sounds strange and it might be better to change the structure of the sentence unless the thing is made up of people (a team, a city, an organisation). For example:
My students, whose homework is never done, will fail the exam.
The homework belongs to the students, it's theirs, so possessive.
That dog whose bone you took is going to bite your leg off.
It is - or was - the dog's bone.
The city, whose football team lost the final, never wins anything.
The city's made up of people, so it sounds OK.
This can be literally translated to mean 'the thing that' or 'that which'. It is not used anywhere near as often as 'which' or 'that' and is not used in the same way. For example:
A man's gotta do what a man's gotta do.
I didn't know what he was going to do next.
Non-defining relative clauses
These are the ones that give extra information. They are always written between commas. If you leave out the relative clause between the commas it still makes sense. For example:
Barcelona, which is Spain's second largest city, is on the Mediterranean coast.
We all know Barcelona, so this is extra information not needed for understanding.
My mother, who is retired, comes to Spain every year.
I used to live in London, where I was born and went to school.
Defining relative clauses
These are the ones that give you the information you need to understand the sentence. There are no commas. If you take the relative clause away, the sentence doesn't make sense. For example:
The team that wins will receive a cup and 1,000 €.
The man who lives next door is always making a noise.
Has he told you what he's going to do?
Has he told me what?
Subject and object relative pronouns
The use of who/which/that may depend on whether the pronoun is the subject or the object of the sentence. For example:
The man who spoke to me told me the story of his life.
He spoke to me, so 'who' is the subject and 'me' is the object.
The man that I spoke to told me the story of his life.
I spoke to him, so 'I' is the subject and 'that' is the object.
When the pronoun is the object it can be left out:
The man I spoke to told me the story of his life.