Non-Defining Relative Clauses (with commas)

Level: B1. A non-defining relative clause drops extra information into a sentence about a person or thing you have already identified. You wrap it in commas, you choose who, which, whose, where or when — and, unlike the defining clauses you met before, you can never use that and never leave the pronoun out.

The rule

A relative clause is a group of words that gives information about a noun. A defining one tells you which noun is meant and is essential: The man who called you is here — without who called you you would not know which man. A non-defining clause is different: the noun is already clear, so the clause only adds a bonus fact. Because that fact is extra, you separate it from the rest with commas.

Compare the two. My sister who lives in Canada is a nurse (defining, no commas) suggests you have more than one sister and are picking out one of them. My sister, who lives in Canada, is a nurse (non-defining, commas) means you have one sister, and by the way she lives in Canada. The commas carry the meaning.

Three things make a non-defining clause behave differently from a defining one. First, you must keep the relative pronoun — you cannot drop it. Second, you cannot use that as the pronoun. Third, the commas are not optional: one before the clause, and one after it if the sentence continues.

A comma followed by which can also comment on a whole earlier clause, not just one noun: She passed the exam, which made her parents proud. Here which means “the fact that she passed”.

Relative pronouns in non-defining clauses

Note the gap in the table: there is no row for that, because that is never used in a non-defining clause.

Defining vs non-defining at a glance

Example sentences

Common mistakes

• ❌ My father, that works in a bank, is kind. → ✅ My father, who works in a bank, is kind. Non-defining clauses never use that.
• ❌ Rome which is in Italy is beautiful. → ✅ Rome, which is in Italy, is beautiful. Extra information needs commas.
• ❌ My sister, I met yesterday, is a doctor. → ✅ My sister, who(m) I met yesterday, is a doctor. You cannot drop the pronoun in a non-defining clause.
• ❌ He passed, what pleased his mother. → ✅ He passed, which pleased his mother. Use which, not what, to comment on a whole clause.
• ❌ My car, which is red it is fast. → ✅ My car, which is red, is fast. Close the clause with a second comma before the sentence continues.
• ❌ Kyoto, which I grew up, is lovely. → ✅ Kyoto, where I grew up, is lovely. Use where for a place, not which.

A short conversation

A: Did you meet Sofia, who just moved here from Spain? B: Not yet. Is she the one whose flat is above the bakery? A: That’s her. She works at the hospital, which is why she’s always busy. B: I’d love to meet her. July, when things are quieter, might be a good time.

Usage notes

• Commas = pauses. When you say a non-defining clause aloud, your voice drops and pauses, exactly where the commas sit. If there is no natural pause, the clause is probably defining.
• whom in object position. In careful or formal writing, whom replaces who when the person is the object: Mr Khan, whom I admire, spoke first. In everyday English, who is normal and fully acceptable.
• No contact clause. In defining clauses you can say the book I read; in non-defining clauses you cannot drop the pronoun — this book, which I read is required.
• Preposition placement. A preposition can go before the pronoun (formal) or at the end (informal): My boss, to whom I reported, left / My boss, who I reported to, left. With that this is impossible, which is another reason that cannot appear here.
• Punctuation at the end. If the non-defining clause ends the sentence, one comma is enough and a full stop closes it: I called Tom, who was asleep.

Compared with…

• The opposite type — essential information, no commas, that allowed, pronoun droppable — is covered in Defining Relative Clauses. Read the two side by side; the comma is the whole difference.
• Longer structures (reduced relatives, of which, clauses inside clauses) build on both types in Advanced Relative Clauses.

Quick recap before you practise.

Practice

Quiz

Recap cheat-sheet

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