Some relative clauses identify or classify nouns: they tell us which person or thing, or which kind of person or thing, is meant. These are called identifying, defining or restrictive relative clauses.
Consider the example given below.
- People who take physical exercise live longer.
Here the relative clause is who take physical exercise. This relative clause is identifying, since it is required for identification: without it, we would have only People live longer, which does not identify the people under discussion.
Other examples are given below.
- The restaurant which we visited last night was pretty good.
- Paris is a city I have always wanted to visit.
- She married a man that she met on a bus.
Identifying relative clauses usually follow immediately after the nouns that they modify, without a break: they are not separated by commas in writing. This is because the noun would be incomplete without the relative clause, and the sentence would make no sense or have a different meaning.
A non-defining relative clause is not required for identification. It serves only to provide additional information. Non-identifying clauses are normally separated by commas.
- Janet, who does my hair, has moved to another hairdresser’s.
Here the relative clause is who does my hair. This relative clause is non-identifying, since it is not required to identify Janet: it merely provides additional information.
Another example is given below.
- She married a smart architect from Beijing, whom she met on a bus.
- This is the boy that won the first prize. (OR … who won the first prize.)
- Here is the man that I told you of. (OR … of whom I told you.)
In non-identifying clauses, that is unusual.
- This is John, who won the first prize. (BUT NOT This is John, that won the first prize.)
In identifying relative clauses, we often leave out object pronouns. In non-identifying clauses this is not possible.
- I still remember the men (whom) I knew in my youth. (identifying)
- Be loyal to the friends (that) you have. (identifying)
- I feel sorry for the man (whom) she married.
- She went to work with my cousin, whom she later married. (NOT She went to work with my cousin, she later married.)