Non-defining relative clauses: extra information with commas

Adding an extra fact

A relative clause is a group of words with a verb that tells you more about a noun. A non-defining clause adds information. You do not need the clause to identify the person or thing.

• My bike, which is ten years old, still works well.
• Nadia, who lives upstairs, has offered to help.

You already know which bike and which person. You can remove the clauses and keep the main message: My bike still works well. Nadia has offered to help.

Who, which, whose and whom

Use who for people and which for things or animals. Who can also refer to a pet. These words can be the subject, doing an action, or the object, receiving an action.

• Omar, who repairs clocks, works from home. Omar does the repairing: who is the subject.
• Omar, who you met yesterday, works from home. You met Omar: who is the object.
• The parcel, which I collected this morning, is for you. I collected the parcel: which is the object.

Keep the pronoun even when it is the object. Do not use that in a non-defining clause.

Whose shows possession. Put a noun after it Whom is a formal alternative to object who. See Whose and whom in relative clauses for these forms in more detail.

• Mei, whose brother is a chef, loves cooking.
• Our former manager, whom we invited, cannot come.

Commas in writing

Put a comma before and after a non-defining clause in the middle of a sentence. At the end of a sentence, put a comma before the clause and finish with the normal sentence punctuation.

• My old laptop, which has a broken screen, is in the cupboard.
• I have lent my keys to Elena, who lives downstairs.

In speaking, you often pause before and after the extra information.

Which for a whole situation

Which can refer to a whole clause or sentence, not only to a noun. Use a comma before it. It can give your opinion about what happened.

• Both lifts stopped working, which made the move difficult. The problem was that both lifts stopped working.
• We finished an hour early, which was a welcome surprise. Finishing early was the surprise.

Use which, not that or what, to introduce this kind of comment.

In conversation, another speaker can add a which-clause as a response. This depends on the first speaker's words; it is not a separate complete sentence in formal writing.

• A: I can collect your tickets this afternoon. B: Which would save me a journey.

Defining or non-defining?

Without commas, a relative clause helps you identify the person or thing. With commas, it gives an extra fact about someone or something already clear.

In the first sentence, the label helps you choose the right suitcase. In the second, my suitcase is already clear. You learn an extra fact about its label.

A name can already identify a person, so a clause after a name often gives extra information. It is the intended meaning, not the name alone, that decides the kind of clause.

What comes next

For information that identifies someone or something, see Defining relative clauses: who, which, that. See Whose and whom in relative clauses for possession and formal whom, and Prepositions in relative clauses: with whom, which... with for prepositions, when and where.