Non-Defining Relative Clauses

What is a Non-Defining Relative Clause?

A non-defining relative clause gives extra, non-essential information about a noun. The noun is usually already specific (e.g., a name, a unique title, or a possessive pronoun like 'my').

The sentence still makes perfect sense if you remove the clause. Think of it as a "by the way" comment.

My brother, who lives in London, is a doctor.

Here, the main information is "My brother is a doctor." The fact that he lives in London is just extra detail. We already know which brother we're talking about.

The Golden Rules of Non-Defining Clauses

1. Always Use Commas

A non-defining clause is always separated from the rest of the sentence by commas. If the clause is in the middle of the sentence, it needs a comma before and after.

The Eiffel Tower, which is in Paris, is famous worldwide.

I'm going to visit my grandmother, who is 90 years old.

2. Never Use "That"

You cannot use the relative pronoun that in a non-defining clause. You must use who for people and which for things.

✗ Incorrect	✓ Correct
My car, that is very old, often breaks down.	My car, which is very old, often breaks down.
Mr. Smith, that is my teacher, is very kind.	Mr. Smith, who is my teacher, is very kind.

3. Never Omit the Pronoun

You cannot omit the relative pronoun (who, which, where, etc.) in a non-defining clause, even if it's the object.

✗ Incorrect	✓ Correct
My boss, I admire a lot, is retiring.	My boss, whom I admire a lot, is retiring.

Pronouns in Non-Defining Clauses

Pronoun	Use	Example
who	People	My friend Sarah, who is a talented musician, is joining a band.
which	Things	My phone, which I only bought last year, is already broken.
whose	Possession	The author, whose books are bestsellers, is giving a talk tonight.
where	Places	London, where my brother lives, is a vibrant city.
whom	People (formal object)	The CEO, whom many people respected, announced his resignation.

Using "Which" to Comment on a Whole Clause

A special feature of non-defining clauses is that which can refer to the entire idea of the preceding clause, not just a single noun.

He forgot my birthday, which made me sad.
(What made me sad? The fact that he forgot my birthday.)

We had to cancel the picnic, which was a real shame.
(What was a shame? The fact that we had to cancel.)

Defining vs. Non-Defining: A Summary

The difference is all about whether the information is essential or just extra.

Feature	Defining Clause	Non-Defining Clause
Purpose	Identifies which noun we mean. (Essential)	Gives extra information about the noun. (Non-essential)
Example	The woman who called you left a message.	My mother, who is a doctor, called me.
Commas	No commas.	Yes, always use commas.
Use of "that"	Yes, can be used for people/things.	No, never use "that."
Pronoun Omission	Yes, if the pronoun is the object.	No, never omit the pronoun.

💡 The key takeaway: If the noun is already specific (like "My father" or "Paris"), any following relative clause is probably non-defining and needs commas and who/which.