B1 · Intermediate

Relative Clauses in English (B1)

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#Grammar
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Relative clauses add detail to a noun and come in two kinds: defining clauses that identify, and non-defining clauses that simply add extra information. This lesson explains both and the punctuation they need.

Relative clauses let you pack more information into a single sentence, and at B1 the focus moves from simply choosing who or which to controlling the difference between defining and non-defining clauses, and knowing when the pronoun can be dropped.

A defining clause identifies which one you mean and is essential to the sentence: The man who fixed the boiler was excellent. Remove it and the listener does not know which man. A non-defining clause adds extra information about something already identified, and it is marked off by commas: My plumber, who fixed the boiler, was excellent.

That distinction has three practical consequences. Non-defining clauses cannot use that; they cannot drop the pronoun; and they always need commas. Defining clauses allow that, allow the pronoun to be omitted when it is the object, and never take commas. Getting this right is one of the clearest markers of B1 writing.

The pronoun is the half most learners already have. The bottom of the drawing is the half that decides punctuation: lift the clause out, and if the sentence can still tell you who is being talked about, the clause was extra and earns its two commas. If it cannot, no commas — and no which standing in for that either.

How to form Defining and Non-Defining Relative Clauses

What each clause type allows — the three differences that matter.
Feature	Defining	Non-defining
Commas	no	yes
Can use that	yes	no
Can omit the pronoun	yes, if it is the object	no, never
Purpose	identifies which one	adds extra detail
Can it be removed?	no, meaning is lost	yes, sentence still works
Example	The book that I bought was cheap.	That book, which I bought yesterday, was cheap.

Defining and Non-Defining Relative Clauses: the key rules

Defining clauses identify which one we mean (no commas); non-defining clauses add extra information between commas.

The colleague who sits next to me is leaving. / Marta, who sits next to me, is leaving.
In non-defining clauses, that is forbidden and the pronoun can never be dropped.

The Louvre, which opened in 1793, is the world's most visited museum.
In defining clauses, the object pronoun can vanish.

The film (which) we watched last night was superb.
Whose shows possession for people and things.

That's the author whose novel won the prize.

When to use Defining and Non-Defining Relative Clauses

Identifying one thing among several

The core job of a defining clause — narrowing down which one you mean.

The train that leaves at six is the fast one.
Adding background detail

Non-defining clauses insert extra information without changing what is being referred to.

My sister, who lives in Oslo, is a translator.
Commenting on a whole clause

Which can refer back to an entire preceding statement, not just a noun.

He arrived two hours late, which annoyed everyone.
Writing more concisely

Relative clauses let you combine short sentences into one fluent structure.

I spoke to the woman whose car was blocking the drive.

Defining vs. non-defining in practice

The commas genuinely change what the sentence claims, so this is a meaning distinction rather than a punctuation preference.

Defining — restricts the meaning

Only some of the group are being referred to. No commas.

The employees who work weekends get extra pay. (only those employees)

Non-defining — describes all of them

The whole group is meant; the clause simply adds information. Commas required.

The employees, who work weekends, get extra pay. (all of them work weekends)

Defining and Non-Defining Relative Clauses in example sentences

The woman who interviewed me was very direct.Defining — identifies which woman.
Dr Sen, who interviewed me, was very direct.Non-defining — she is already identified.
The report that I sent contains the figures.Defining with that.
The report I sent contains the figures.Object pronoun omitted — only possible in defining clauses.
This is the village where my father grew up.where for a place.
She failed the exam, which surprised everybody.which referring to the whole previous clause.
The candidate whose references were strongest got the job.whose showing possession.
The people with whom I worked were excellent.Formal structure — preposition before whom.

Defining and Non-Defining Relative Clauses in a real conversation

Listen for the commas — they tell you whether the clause is identifying or simply adding detail.

Recruiter:The candidate who called yesterday has withdrawn.

Head:Which one? The engineer whose portfolio we liked?

Recruiter:No, the other one. Petra, who interviewed on Monday, is still interested.

Head:Good. She's the one I'd prefer anyway.

Recruiter:The role, which was advertised internally first, had forty applicants.

Head:Then let's move quickly, which means deciding this week.

Common mistakes (and how to fix them)

My brother, that lives in Madrid, is visiting.

My brother, who lives in Madrid, is visiting.

Between commas, that cannot introduce the clause — use who or which.
The book what you lent me was great.

The book (that/which) you lent me was great.

What is never a relative pronoun after a noun — it means 'the thing that'.
The people which live upstairs are noisy.

The people who live upstairs are noisy.

People take who; which is reserved for things.

Practise Defining and Non-Defining Relative Clauses today

Punctuation is where the marks are — practise adding and removing commas deliberately.

Write four defining and four non-defining clauses about people you know.
Take four defining sentences and add commas — explain how the meaning changes.
Mark which of your defining clauses could drop the relative pronoun.
Combine these: I read a book. It changed my mind. / My boss is retiring. She started in 1998.

Defining and Non-Defining Relative Clauses: frequently asked questions

When exactly can I omit the relative pronoun?

Only when two conditions are both met: the clause is defining, and the pronoun is the object of that clause. The film I watched works because I is the subject and the pronoun was the object. The film that won works only with the pronoun, because there the pronoun is the subject. A quick test is to look at the next word — if a subject follows immediately, the pronoun can go.

Why can I not use that in a non-defining clause?

It is a fixed convention of standard English rather than a logical necessity. Non-defining clauses take who for people and which for things: My car, which is ten years old, still runs well. Writing My car, that is ten years old is considered an error in careful writing and is penalised in exams. That belongs exclusively to defining clauses.

Can which refer to a whole sentence?

Yes, and it is very useful. In He forgot the tickets, which meant we missed the film, which refers to the entire preceding clause rather than to any single noun. This use is always non-defining and always takes a comma. Note that what cannot do this job in standard English — He forgot the tickets, what meant we missed the film is wrong.

Is whom still necessary?

Rarely. Whom is the object form, and modern English overwhelmingly uses who in both positions. Whom survives mainly directly after a preposition — to whom, for whom, with whom — and in formal writing. The people with whom I worked is correct but formal; The people I worked with is far more natural. Using whom incorrectly reads worse than not using it at all.