What is a Non-defining Relative Clauses?
A non-defining relative clause (also called a non-restrictive relative clause) adds extra, parenthetical information about a noun that is already clearly identified. The information is interesting or useful, but the sentence would still make complete sense without it.
The key signals are the commas. A non-defining clause is always wrapped in commas (or a comma and a full stop at the end of a sentence) — they work like brackets. For example: "My brother, who lives in Edinburgh, is visiting next week." Removing the relative clause leaves a complete, meaningful sentence.
Two absolute rules: non-defining relative clauses always use commas, and they never use that. These have no exceptions.
How to Form a Non-defining Relative Clause
The relative pronoun is always required — it can never be omitted. The pronoun set is smaller than in defining clauses: who for people, which for things (and whole clauses), whose for possession, where for specific places, and when for specific times. That is never used.
Specific noun , who / which / whose / where / when + clause ,Relative Pronouns in Non-defining Clauses
| Pronoun | Refers to | Can be omitted? | Example |
|---|---|---|---|
| who | People | No | Maria, who I met at the conference, is a surgeon. |
| which | Things | No | His new novel, which I read in one sitting, is outstanding. |
| whose | People or things | No | Professor Hall, whose research I admire, retired last year. |
| where | Specific places | No | We visited Kyoto, where the cherry blossoms were in full bloom. |
| when | Specific times | No | She was born in 1990, when the internet was still in its infancy. |
| which (clause) | Whole previous clause | No | He apologised immediately, which surprised everyone. |
When to Use Non-defining Relative Clauses
Adding extra information about a specific person — who
We use who to add non-essential facts about a person who is already clearly identified by their name, title, or unique description. The clause could be lifted out without changing who we are talking about.
- My grandfather, who fought in the Second World War, rarely talked about his experiences.
- The CEO, who has led the company for fifteen years, announced her retirement yesterday.
- Leonardo da Vinci, who was born in 1452, is considered one of history's greatest minds.
Adding extra information about a specific thing — which
We use which (never that) to add extra details about a specific object, place, idea, or concept. The noun must already be identifiable — it is a specific one, not an unnamed member of a group.
- Her debut album, which sold over two million copies, made her an overnight star.
- The Louvre, which houses the Mona Lisa, is the most visited museum in the world.
- The treaty, which was signed in 1919, reshaped the political map of Europe.
Showing possession — whose
We use whose in non-defining clauses just as in defining ones — to show that something belongs to the noun. The difference is purely the commas: the noun is already identified, so the whose-clause adds extra context rather than identifying it.
- Dr Patel, whose paper I read last week, will be presenting at the conference.
- The old cathedral, whose spire was damaged in the storm, is now undergoing restoration.
- My neighbour, whose dog woke us up every morning, has finally moved away.
Commenting on an entire previous clause — which
One of the most distinctive uses: which can refer back to the whole previous clause, not just a single noun. This is sometimes called a "sentential relative clause." It is used to add a comment, reaction, or consequence to an entire idea.
- She finished the project three days early, which impressed the whole team.
- He never apologised for what he said, which made things very awkward at work.
- They cancelled the event at the last minute, which left hundreds of people disappointed.
Adding context about a specific place or time — where and when
We use where after a specific, named place and when after a specific, named time to give extra context. The time or place is already identified — we are simply adding a detail about it.
- I grew up in a small village in Cornwall, where everyone knew each other.
- The summit took place in Geneva, where world leaders gathered to sign the agreement.
- The film is set in the 1960s, when the space race was at its height.
Relative Pronouns at a Glance
Defining vs. Non-defining: The Critical Contrast
The choice between defining and non-defining is not stylistic — it changes the meaning of the sentence. This is the most important distinction in this area of grammar.
Defining (no commas) — identifies
Students who fail the test must resit it.
Only the students who fail must resit. The clause identifies which students — the others are fine. Without the clause, we don't know who must resit.
Non-defining (with commas) — adds a comment
The students, who had all studied hard, passed the test.
All the students passed. The clause adds background information — it doesn't narrow down which students. Remove it: "The students passed the test." — still complete.
Defining — one specific brother is meant
My brother who lives in Tokyo called me last night.
The speaker has more than one brother. The clause tells us which one — the Tokyo one. Essential information.
Non-defining — only one brother exists
My brother, who lives in Tokyo, called me last night.
The speaker has only one brother. Tokyo is just extra detail — interesting, but not needed to identify him. Commas signal this.
Defining — that IS possible
The film that won the award was remarkable.
That is fine in defining clauses. It identifies which film out of many possible films.
Non-defining — that is NEVER possible
Parasite, which won the award, was remarkable.
We use which, never that, in non-defining clauses. The film is already named — the clause only adds a comment.
Quick test: does the clause tell you which specific person or thing? → Defining (no commas). Does it just add information about an already-identified noun? → Non-defining (use commas).
Common Mistakes
Forgetting the commas
✗ My sister who is a dentist lives in Manchester.
✓ My sister, who is a dentist, lives in Manchester.
If the speaker has only one sister, "who is a dentist" is non-essential information. Without commas, the sentence reads as though there are multiple sisters and only the dentist one lives in Manchester. Commas signal the clause type and change the meaning.
Using "that" instead of "who" or "which"
✗ The Great Wall of China, that stretches over 21,000 km, took centuries to build.
✓ The Great Wall of China, which stretches over 21,000 km, took centuries to build.
That is never used in non-defining relative clauses — not for things, not for people. Use which for things and who for people. This is an absolute rule, heavily tested in B2 examinations.
Omitting the relative pronoun
✗ The book, I read last summer, changed my perspective completely.
✓ The book, which I read last summer, changed my perspective completely.
Unlike defining clauses, non-defining clauses never allow the relative pronoun to be omitted. In defining clauses you can say "the book I read" (omitting that/which). In non-defining clauses, which must always be present.
Using a non-defining clause when a defining clause is needed
✗ I want to thank the colleagues, who helped me with this project.
✓ I want to thank the colleagues who helped me with this project.
With commas, the sentence implies all colleagues helped. Without commas, the defining clause correctly identifies which colleagues: those who helped, not all. Ask yourself: does the clause narrow down which one(s), or just add information about an already-identified noun?
Missing the comma before which in a sentential clause
✗ She passed all her exams which made her parents very proud.
✓ She passed all her exams, which made her parents very proud.
When which refers back to an entire clause, a comma before it is essential. Without the comma, "which" looks like a defining pronoun referring to "exams". The comma clarifies that which comments on the whole previous situation.
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