Relative clauses: how you combine two ideas into one.
A relative clause adds information about a noun using who, which, that, whose, where or when. It is the main tool for turning two short sentences into one fuller one, “The report was hers. It won the prize.” becomes “The report that won the prize was hers.” Doing this well, with the comma rule kept straight, is one of the clearest ways grammar moves from Band 6 to Band 7+.
Why this matters. Examiners reward a range of complex sentences used accurately. Relative clauses are the most useful way to build them: instead of two flat sentences, you embed one inside the other (“Cities that invest in transport tend to grow faster”). The whole skill rests on two distinctions, defining (it tells you which noun, no commas) versus non-defining (it adds extra detail, with commas), and knowing when you can drop the relative pronoun. Get the comma rule wrong and a Band 7 sentence reads as a Band 6 one.
One clause, slotted next to a noun, telling you more about it.
A relative clause comes straight after the noun it describes and usually opens with a relative pronoun: who (people), which (things), that (people or things, defining only), whose (possession), where (places), when (times).
Defining clauses
who · which · that · (no commas)
Tell the reader which noun you mean. The sentence loses its sense without them, so they take no commas. That is allowed here.
The students who finished early left. (which students? the ones who finished)
Non-defining clauses
who · which · , commas , · never that
Add extra, removable detail about a noun already identified. They are fenced off with commas, and that is not used.
My supervisor, who studied in Berlin, speaks four languages.
Dropping the pronoun
the book [that] I read
When the relative pronoun is the object of its clause, you can leave it out, a natural, economical Band 7 move. You cannot drop a subject pronoun.
The film (that) I watched was long. But not a subject: the man who called.
whose, where, and which for a whole idea
whose · where / when · , which
Use whose for possession, where / when for place and time, and a non-defining which to comment on the whole previous clause.
Sales fell sharply, which surprised analysts.
The errors that mark you down
Three are common. No second pronoun: the relative word already is the subject or object, so “the man who he came” is wrong, just “the man who came”. The comma rule: a defining clause takes no commas (“people who exercise live longer”), a non-defining one needs them on both sides. No that after a comma: non-defining clauses use who / which, never that, and never “what” as a relative pronoun.
What relative-clause control reads like at each band.
At Band 5
Relative clauses are mostly avoided; when attempted, a second pronoun slips in (the man who he came) or which is used for people. The comma rule is not observed, and ideas that a relative clause would join are left as separate short sentences instead.
At Band 6
A few relative clauses appear, almost always defining and almost always with that or which. Commas are unreliable, the non-defining comma is often missing or added to a defining clause. A resumptive pronoun sometimes slips in (“the people who they live here”). Sentences stay mostly short and separate.
At Band 7
Relative clauses are used to combine ideas, with both defining and non-defining forms and the comma rule mostly right. Whose and where turn up, and the object pronoun is sometimes dropped naturally (“the data I collected”). The odd comma slip survives but does not obscure meaning.
At Band 8+
The full range, controlled and purposeful: non-defining clauses for added comment, a clause-final which commenting on a whole statement (“…, which is rarely acknowledged”), and, where the register suits it, a fronted preposition (“the framework on which the policy rests”). Punctuation is accurate throughout.
Pick the word from what the clause is doing.
Decide what the clause refers to, a person, a thing, a possessor, a place, a time, or the whole previous idea, and whether it is essential (defining) or extra (non-defining). The word follows.
| The clause refers to… | Use… | For example |
|---|---|---|
| A person (essential) | who / that | The candidate who scored highest was offered the place. |
| A thing (essential) | which / that | Policies that reduce emissions are gaining support. |
| Extra detail (non-essential) | , who / , which , | The new library, which opened in March, is already full. |
| Possession | whose | A company whose profits fell still hired staff. |
| A place | where | The region where the study took place is rural. |
| A time | when | 2008, when the crisis began, changed everything. |
| A whole previous statement | , which | Numbers rose every year, which the model had not predicted. |
that vs which. In a defining clause, both are usually fine (“the report that/which won”); in British English which is perfectly acceptable. In a non-defining clause, after a comma, you must use which (or who), never that. For combining ideas with conjunctions and clause types more broadly, work through sentence structure →
Ten to drill.
Choose the modal that fits the meaning. Press Check answers for your score and the reason behind each one. Nothing is sent anywhere.
You can name the relative pronouns. Combining ideas cleanly, with the commas right, under timed pressure is the work.
The comma rule and the dropped pronoun are easy to follow on the page and easy to lose in a real Task 2 paragraph, where the marks are won or lost.
In a lesson I push you to combine your own short sentences into relative clauses as you write and speak, and I flag the missing comma or the doubled subject the moment it appears. Lessons are £20 for fifty minutes, one to one, in proper British English; the first step is a free 25-minute introduction. This page is adapted from the grammar chapter of the forthcoming Ultimate Guide to IELTS Speaking.