When can you leave out the relative pronoun?

In defining clauses you can drop the pronoun when it is the object: 'The book I read.' If it is the subject you cannot: 'The man who lives here.' Don't drop it in non-defining clauses.

Do you use 'who' or 'which' for people and things?

Use 'who' for people and 'which' for things: 'the person who called', 'the car which/that I bought'. 'The car who I bought' and 'the person which called' are wrong.

Grammar Level B1

Relative Clauses: Who, Which, That

Q: What is the difference between defining and non-defining relative clauses?

Defining clauses identify which one and take no commas; non-defining clauses add extra information, use commas, and don't use 'that' — use 'who' or 'which'.

How relative clauses work in English: who, which, that, where and whose, defining vs non-defining, when to drop the pronoun, and the mistakes to avoid.

name a noun · then add who / which / that

A relative clause adds information about a noun without starting a new sentence: the man who lives next door, the book that I read. It's how you join two short sentences into one natural one. The main system is choosing the right relative pronoun, knowing whether the clause is defining or non-defining, and knowing when you can leave the pronoun out.

Which pronoun?

who — people. The woman who called you is here.

which — things, especially in non-defining clauses; also possible in defining clauses. The phone which I bought is great. / My phone, which I bought last year, still works well.

that — people or things in defining clauses; very common, especially in speech. The movie that we saw…

where (places), whose (possession), when (times). the city where I grew up · the man whose car…

When you can drop the pronoun

In defining relative clauses, if the relative pronoun is the object of the clause, you can leave it out. If it's the subject, you can't. In non-defining clauses, don't leave the pronoun out.

The book (that) I read… (object — drop it: "The book I read")
The man who lives here… (subject — keep it)
My brother, who lives in Rome, is a chef. (non-defining — keep it; not "My brother, lives in Rome, is a chef")

Defining vs non-defining

Defining clauses identify which one — no commas. Non-defining clauses add extra information — use commas, and don't use that. Use who for people, which for things or whole ideas, and whose for possession.

The students who passed got a certificate. (defining — which students)
My brother, who lives in Rome, is a chef. (non-defining — extra info)
My laptop, which I bought last year, still works well. (non-defining — a thing)

Common mistakes

Repeating the subject/object pronoun.

✕The book that I read it was good.
✓The book that I read was good.

Using who for a thing or which for a person.

✕the car who I bought · the person which called
✓the car which/that I bought · the person who called

"that" in a non-defining clause. "My boss, that is German, ..." → My boss, who is German, ... Use who/which in non-defining clauses, not that.

Quick exercise

Add the right relative pronoun (or — if it can be left out).

That's the woman ___ won the prize.
This is the house ___ we lived in.
She has a friend ___ brother is famous.
The restaurant ___ we ate dinner was lovely.
Paris, ___ is the capital of France, is beautiful.

Answer key

who/that (subject — can't drop)
which/that/— (object — can drop)
whose (possession)
where (place)
which (non-defining — not "that")

Practice this in Recursio

Relative clauses are how you join two ideas into one smooth sentence — and the who/which/that choice, commas, and dropped pronouns are easy to slip on. Recursio's AI Coach drills them in real sentences and the Daily Mixed Review keeps the patterns coming back until they feel natural.

Practice grammar in Recursio → · Free to start, on iOS and Android.