Simple explanation
What is a non-defining relative clause? A non-defining relative clause adds extra information about a person, thing, or place that is already clear or identified. The extra information is useful, but we do not need it to understand who or what the speaker means. Why is the information extra? Consider this sentence: My brother, who lives in London, is a doctor. The words who lives in London give us more information about my brother. If we remove them, My brother is a doctor is still complete and understandable. This is a key feature of a non-defining relative clause. How is it different from a defining relative clause? A defining relative clause tells us which person or thing we mean, so its information is necessary. A non-defining relative clause adds information about someone or something already identified. Compare: The students who studied passed the exam. Here, who studied identifies which students passed. In Tom, who studied all weekend, passed the exam, Tom is already identified and the relative clause simply adds information about him. Why do we use commas? In writing, commas separate a non-defining relative clause from the main part of the sentence. If the relative clause appears in the middle, it normally has a comma before and after it. If it comes at the end, it normally has a comma before it. These commas help show that the information is additional rather than necessary for identification. Which relative words can we use? We normally use who for people, which for things, whose for possession or relationships, and where for places. In standard English, that is not normally used in non-defining relative clauses. We also do not omit an object relative pronoun such as who or which in this type of clause.
Grammar formula
Extra information about a person
person, + who + clause, + main clauseMy sister, who lives in Canada, is visiting us.
Extra information about a thing
thing, + which + clause, + main clauseMy phone, which is quite old, still works well.
Possession or relationship
person, + whose + noun + clause, + main clauseAnna, whose brother is a doctor, lives nearby.
Extra information about a place
place, + where + clause, + main clauseOxford, where my father studied, is a beautiful city.
Relative clause at the end
main clause, + relative word + clauseI spoke to David, who was waiting outside.
Core rules
- 1
Use who for people
Use who when the extra information is about a person: Emma, who works with my sister, lives nearby.
- 2
Use which for things
Use which when the extra information is about a thing: My laptop, which is five years old, still works well.
- 3
Use whose for possession
Use whose to show possession or a relationship: Daniel, whose sister lives in Canada, visits her every summer.
- 4
Use where for places
Use where when the extra information describes what happens or happened in a particular place: Oxford, where my father studied, is a beautiful city.
- 5
Separate extra information with commas
A non-defining relative clause must be separated from the main sentence by commas: Julia, who speaks Spanish, works with international clients. When the clause is in the middle of the sentence, it normally needs two commas.
- 6
Do not normally use that
That is not normally used to introduce a non-defining relative clause in standard English. Say My car, which is very old, still runs well, not My car, that is very old, still runs well.
- 7
Do not omit the relative pronoun
In non-defining relative clauses, an object relative pronoun is not normally omitted. We say My bike, which I bought last year, is already broken, not My bike, I bought last year, is already broken.
Useful examples
My brother, who lives in Manchester, is coming to visit us.
My brother lives in Manchester, and he is coming to visit us.
The brother is already identified; who lives in Manchester only adds extra information.
Our car, which is more than ten years old, still runs well.
Our car is over ten years old, but it still works well.
Which introduces extra information about a specific car.
Maya, whose father is a chef, loves cooking.
Maya's father is a chef, and Maya loves cooking.
Whose shows the relationship between Maya and her father.
Paris, where we spent our honeymoon, was unforgettable.
We spent our honeymoon in Paris, and the experience there was unforgettable.
Where introduces extra information about a clearly identified place.
I called David, who was waiting for me outside.
I called David, and he was waiting for me outside.
The relative clause comes at the end, so a comma separates it from the main clause.
This jacket, which my sister gave me, is really warm.
My sister gave me this jacket, and it is really warm.
Which is the object of gave, but it cannot be omitted in this non-defining clause.
Mr Harris, who teaches us history, is moving to another school.
Mr Harris teaches us history, and he is moving to another school.
Mr Harris is already identified by name, so the clause adds information rather than identifying him.
My neighbour, whose dog often plays in our garden, is very friendly.
My neighbour has a dog that often plays in our garden, and the neighbour is very friendly.
Whose expresses possession: the dog belongs to the neighbour.
The new library, which opened last month, is already very popular.
The new library opened last month, and it is already very popular.
Which is the subject of opened in the relative clause.
We stayed in Oxford, where my mother studied many years ago.
We stayed in Oxford, and my mother studied there many years ago.
Where has the meaning of in that place.
My old laptop, which I use for studying, is getting very slow.
I use my old laptop for studying, and it is becoming very slow.
The relative clause gives extra information about an already identified laptop.
Sophie, who I met at university, now works in Germany.
I met Sophie at university, and she now works in Germany.
Who is the object of met. Even as an object, it is not omitted in this non-defining clause.
Common mistakes
- ❌ My car, that I bought last year, is very reliable. ✅ My car, which I bought last year, is very reliable. In standard English, that is not normally used in a non-defining relative clause. Use which for things.
- ❌ Anna who lives next door is a nurse. ✅ Anna, who lives next door, is a nurse. Anna is already identified by name, and who lives next door is extra information, so commas are needed.
- ❌ My friend, which works at a bank, is moving abroad. ✅ My friend, who works at a bank, is moving abroad. Use who for a person, not which.
- ❌ My laptop, I bought last year, is already broken. ✅ My laptop, which I bought last year, is already broken. An object relative pronoun such as which cannot normally be omitted in a non-defining relative clause.
- ❌ London, which I lived for two years, is very expensive. ✅ London, where I lived for two years, is very expensive. The intended meaning is in London or in that place, so where is the natural relative word.
- ❌ Emma, who mother is a teacher, speaks French. ✅ Emma, whose mother is a teacher, speaks French. The sentence expresses a relationship between Emma and her mother, so whose is required.
Learning tips
- Use the removal test: take out the relative clause. If the sentence still clearly identifies the person or thing, the clause may be non-defining.
- Names such as Emma, Berlin, and Mr Harris often refer to already identified people or places, so a following relative clause is often non-defining. Always check the meaning and context, however.
- Remember the basic B1 pattern: person → who, thing → which, possession → whose, place → where.
- Commas are not just decoration. They help show that the information is additional rather than necessary for identification.
- When writing, create the complete main sentence first. Then add the extra information with the appropriate relative word and commas.
- Do not automatically translate every relative word as the same form. Choose who, which, whose, or where according to the meaning and grammatical role.
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PlannedRelated grammar
Related dictionary words
Frequently asked questions
What is the main difference between defining and non-defining relative clauses?
A defining relative clause gives information needed to identify the person or thing. A non-defining relative clause adds extra information about someone or something that is already identified.
Can I use that in a non-defining relative clause?
Normally no. In standard English, use forms such as who for people and which for things instead.
Do non-defining relative clauses always need commas?
In standard written English, yes. A clause in the middle of a sentence is normally surrounded by two commas, while a clause at the end normally has a comma before it.
Can I leave out who or which when it is the object?
Not normally in a non-defining relative clause. For example, My bike, which I bought last year, is very reliable keeps which even though it is the object of bought.
When should I use whose instead of who?
Use whose when you need to express possession or another relationship, as in Lisa, whose brother is a doctor, lives nearby. Use who when the relative pronoun refers directly to the person.
How can I quickly recognize a non-defining relative clause?
Ask whether the person or thing is already clear without the relative clause. If it is, and the clause simply adds extra information, the clause is probably non-defining. Commas are another important clue in writing.