Relative clauses are who, whom, that,which, whose, where or what.
A relative clause is the part of the sentence which denotes which person
or thing your sentence is about.
e.g. 1. The woman who lives next door works as a nurse.
The sentence is referring to one woman, the woman living next door, therefore who is used.
The chair that I am sitting on belonged to my grandmother.
The sentence is referring to a particular chair, the one which the speaker is sitting on, therefore that is used.
Who is used with people.
That and Which are used with inanimate objects or unidentified living things.
n.b. When speaking about unidentified animals which and that are usually used, however, it is increasingly common to use who when speaking about named animals in English.
e.g. Red Rum, who won the derby, was a well bred race horse.
Extra Information Clauses.
Normally when using relative clauses in English they reinforce the person or thing the sentence is referring to. This is the case with the examples given above. This type of relative clause could be referred to as a necessary information clauseor more commonly a defining relative clause, as without this information the reader would be unsure which person or thing is being spoken about.
Relative clauses are not only used to give necessary information however. Compare the following sentences.
The essay which you are writing should be finished by Friday.
Peter’s essay, which he is writing, should be finished by Friday.
The second sentence differs from the first because it does not give necessary information about which essay the sentence refers to (we are immediately told it is Peter’s essay). Instead the sentence gives us some extra information about the essay (Peter is writing the essay now). This is an extra information clause.
Relative clauses are used to provide extra information only when the person or thing referred to in a sentence is clearly defined immediately. This means that the person or thing will have a unique name or will have adjectives or other describing words attached to it. Study the following examples.
Rachael Bradford, who you met at my birthday party, is a very pleasant girl.
The subject of the sentence is immediately named, therefore the fact that she was at the birthday party is extra information.
The big blue ball, which we were playing with yesterday, is in the shed.
The subject of the sentence is immediately described, therefore the fact that it was being played with yesterday is extra information.