When to set off relative clauses with commas

Relative clauses are clauses introduced by the relative pronouns who, which, that, whom and whose.

Relative clauses are also called adjective clauses. A relative clause modifies a noun or pronoun in another clause. It also connects the two clauses.

Study the examples given below.

• I know the girl who won the first prize.

Here the relative clause ‘who won the first prize’ modifies the noun ‘girl’. It also connects the two clauses: ‘I know the girl’ and ‘she won the first prize’.

• People who exercise regularly live longer.

Here the relative clause ‘who exercise regularly’ modifies the noun ‘people’. It also connects the two clauses: ‘People exercise regularly’ and ‘They live longer’.

There are two types of relative clauses: identifying relative clauses and non-identifying relative clauses.

Identifying relative clauses tell us which person or thing is meant. They are also called ‘defining’ or ‘restrictive relative clauses’.

• The woman who babysits my children has moved to another city.

Here the relative clause ‘who babysits my children’ answers the question ‘which woman?’. Therefore it is an identifying relative clause.

If you remove an identifying relative clause from the sentence some meaning will be lost.

Consider the sentence, ‘The woman has moved to another city’. It makes sense but it does not explain which woman we are talking about.

Identifying clauses usually follow immediately after the noun that they modify. They are not separated by commas in writing.

More examples of identifying relative clauses are given below.

• This is the house that Jack built. (Which house? The one that Jack built)

• The girl who won the first prize is my neighbor’s daughter. (Which girl? The one who won the first prize)
• The laptop that I bought for my sister was very expensive. (Which laptop? The one I bought for my sister)
• The girl who answered the phone was very polite. (Which girl? The one who answered the phone)

Some relative clauses merely provide additional information. They do not identify or classify. These are called non-identifying, non-defining or non-restrictive relative clauses.

Non-identifying relative clauses are separated by commas.

• My sister, who lives in the US, is a nurse.

Here you don’t need the relative clause ‘who lives in the US’ to figure out which woman I am talking about. I have already made it clear that I am talking about my sister. In this case, the relative pronoun merely provides additional information. Therefore, it is a non-identifying relative clause.

More examples are given below.

• Maria, who babysits my children, lives with her aged parents.

Here the relative clause ‘who babysits my children’ does not identify the woman. She has already been identified by her name.

• Rahul, who was my junior at college, is now my boss.