Relative clauses are clauses starting with the relative pronouns who*, that, which, whose, where, when. They are most often used to define or identify the noun that precedes them. Here are some examples:
* There is a relative pronoun whom, which can be used as the object of the relative clause. For example: My science teacher is a person whom I like very much. To many people the word whom now sounds old-fashioned, and it is rarely used in spoken English.
Relative pronouns are associated as follows with their preceding noun:
|Preceding noun||Relative pronoun||Examples|
|a person||who(m)/that, whose||- Do you know the girl who ..|
- He was a man that ..
- An orphan is a child whose parents ..
|a thing||which†/that, whose||- Do you have a computer which ..|
- The oak a tree that ..
- This is a book whose author ..
Note 1: The relative pronoun whose is used in place of the possessive pronoun. It must be followed by a noun. Example: There's a boy in grade 8 whose father is a professional tennis player. (There's a boy in grade 8. His father is a professional tennis player.)
Note 2: The relative pronouns where and when are used with place and time nouns. Examples: FIS is a school where children from more than 50 countries are educated. 2001 was the year when terrorists attacked the Twin Towers in New York.
Some relative clauses are not used to define or identify the preceding noun but to give extra information about it. Here are some examples:
Note 1: Relative clauses which give extra information, as in the example sentences above, must be separated off by commas.
Note 2: The relative pronoun that cannot be used to introduce an extra-information (non-defining) clause about a person. Wrong: Neil Armstrong, that was born in 1930, was the first man to stand on the moon. Correct: Neil Armstrong, who was born in 1930, was the first man to stand on the moon.
There are two common occasions, particularly in spoken English, when the relative pronoun is omitted:
1. When the pronoun is the object of the relative clause. In the following sentences the pronoun that can be left out is enclosed in (brackets):
Note: You cannot omit the relative pronoun a.) if it starts a non-defining relative clause, or, b.) if it is the subject of a defining relative clause. For example, who is necessary in the following sentence: What's the name of the girl who won the tennis tournament?
2. When the relative clause contains a present or past participle and the auxiliary verb to be. In such cases both relative pronoun and auxiliary can be left out:
† Some native speakers, particularly those from the USA, consider it a mistake to use which in a defining/restrictive relative clause. Advanced learners of English can read more about this on Language Log.