Relative Clauses (Defining & Non-Defining)

Relative clauses are one of the most versatile tools in the IELTS candidate's grammar toolkit. They allow you to combine ideas smoothly, add detail to nouns, and create the complex sentences that the examiner is looking for. However, the distinction between defining and non-defining relative clauses — and the punctuation rules that go with them — is a frequent source of errors.

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What Is a Relative Clause?

A relative clause is a subordinate clause that modifies a noun. It begins with a relative pronoun:

Pronoun	Use
who	people (subject)
whom	people (object — formal)
which	things
that	people or things (defining clauses only)
whose	possession (people or things)
where	places
when	times

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Defining Relative Clauses

A defining (also called restrictive) relative clause identifies which person or thing we are talking about. Without it, the sentence is incomplete or unclear.

Students who study regularly tend to achieve higher band scores.

If we remove "who study regularly", the meaning changes entirely — we no longer know which students we mean.

Key Rules for Defining Clauses

1. No commas around the clause
2. "That" can replace "who" or "which"
3. The relative pronoun can be omitted when it is the object of the clause

Pronoun as subject (cannot be omitted):

The country that/which has the highest GDP is the United States.

Pronoun as object (can be omitted):

The book (that/which) I read last week was fascinating.

The person (who/whom/that) I met at the conference was an expert in climate science.

Examples for IELTS

People who live in urban areas often experience higher levels of stress.

The measures that governments have implemented appear to be effective.

The period when the most significant growth occurred was between 2005 and 2015.

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Non-Defining Relative Clauses

A non-defining (also called non-restrictive) relative clause adds extra information about a noun that is already clearly identified. The information is interesting or useful but not essential.

China, which is the world's most populous country, has experienced rapid economic growth.

We already know which country we mean — "China" is specific. The relative clause adds supplementary information.

Key Rules for Non-Defining Clauses

1. Commas are required — before and after the clause (or before and full stop if at the end)
2. "That" CANNOT be used — use only who, which, whose, where, when
3. The relative pronoun CANNOT be omitted

Correct:

London, which is the capital of the UK, attracts millions of tourists each year. ✅

Incorrect:

London, that is the capital of the UK, attracts millions of tourists each year. ❌

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Defining vs Non-Defining: The Crucial Difference

Consider these two sentences:

1. The students who passed the exam were given certificates. (DEFINING — only the students who passed)

2. The students, who passed the exam, were given certificates. (NON-DEFINING — all the students, and by the way they all passed)

The commas completely change the meaning. In sentence 1, some students passed and some didn't. In sentence 2, all students passed.

More examples: