Defining vs Non-defining Relative Clauses
Relative clauses add information about a noun. But there are two types — one is essential to the meaning, and the other is extra detail. Getting this distinction right matters for both grammar and punctuation.
Defining relative clauses
A defining (restrictive) relative clause identifies which person or thing we are talking about. It is essential — remove it and the meaning changes or is lost. No commas are used.
The woman who called you is my sister. (which woman? → the one who called)
The book that I recommended is out of print.
The house where I grew up has been demolished.
Non-defining relative clauses
A non-defining (non-restrictive) relative clause adds extra information about a noun that is already clearly identified. Remove it and the sentence still makes complete sense. Commas are always used.
My sister, who lives in Paris, is visiting next week.
The Eiffel Tower, which was built in 1889, attracts millions of visitors.
Key differences
| Defining | Non-defining | |
|---|---|---|
| Commas | No commas | Commas required |
| Essential? | Yes — identifies the noun | No — adds extra information |
| Can use 'that'? | Yes | No — use who / which / whom |
| Can omit pronoun? | Yes (if object) | No |
That, who, and which
In defining clauses, you can use that for people or things. In non-defining clauses, that cannot be used.
Inception, which I watched last night, was brilliant. ✓
Inception, that I watched last night, was brilliant. ✗
Omitting the relative pronoun
In defining clauses, you can drop the pronoun when it is the object of the clause.
The book (that) I read last week was fascinating.
The person (who) you need to speak to is Sara.
Never drop the pronoun in non-defining clauses. "My mother, who is a doctor, lives in Madrid." The pronoun cannot be omitted.
Quick test: Cover up the relative clause. If the sentence still clearly refers to the right person or thing, it is non-defining (add commas). If covering it creates ambiguity, it is defining (no commas).