A relative clause is a type of subordinate clause that modifies a noun or pronoun by giving additional information about it. Rather than writing two short sentences, you can combine them into one more fluent sentence using a relative pronoun. For example, instead of I met a woman. She speaks five languages. you can write I met a woman who speaks five languages. At B1–B2 level, mastering relative clauses is one of the most reliable ways to improve both writing complexity and spoken fluency.
What You'll Learn
- How to choose correctly between who, which, that and whose depending on what the antecedent refers to.
- The difference between defining (restrictive) and non-defining (non-restrictive) relative clauses and when to use commas.
- When that can replace who or which — and the contexts where it cannot.
- How to omit the relative pronoun when it acts as the object of the clause (contact clauses).
Choosing the Right Relative Pronoun
The choice of relative pronoun depends on what the clause refers to and what grammatical role the pronoun plays within the clause.
- who — refers to people: The teacher who taught me French retired last year.
- which — refers to things and animals: The book which I borrowed was fascinating.
- that — refers to people or things in defining clauses: The car that she bought broke down immediately.
- whose — shows possession for people or things: The student whose essay won the prize is in my class.
- where — refers to a place: The city where I grew up has changed a lot.
- when — refers to a time: I remember the year when we moved house.
Defining Relative Clauses
A defining (or restrictive) relative clause identifies which person or thing is being referred to. Without it, the sentence would be unclear or incomplete. No commas are used. Either that or who/which can be used.
- The film that/which we watched last night was brilliant.
- The man that/who called you yesterday is my neighbour.
- This is the house that/which Jack built.
When the relative pronoun is the object of the verb in the relative clause, it can be omitted entirely. This is called a contact clause: The film (that) we watched was brilliant.
Non-Defining Relative Clauses
A non-defining (or non-restrictive) relative clause adds extra, non-essential information about a noun that is already clearly identified. It is always separated from the main clause by commas. Crucially, that cannot be used in non-defining clauses.
- My sister, who lives in Edinburgh, is visiting us next week.
- The Eiffel Tower, which was built in 1889, attracts millions of visitors every year.
- Professor Hall, whose research I admire greatly, gave a lecture last Tuesday.
If you remove a non-defining relative clause, the sentence remains grammatically complete and its meaning is still clear. The clause simply adds interesting or useful detail.
Using whose
Whose is the possessive relative pronoun. It replaces his, her, its or their and can refer to both people and things. It is used in both defining and non-defining clauses.
- The woman whose bag was stolen reported it to the police. (defining)
- Oxford, whose university dates back to the 12th century, is a popular tourist destination. (non-defining)
Practice Exercises
Work through the exercises below to put your knowledge of relative clauses to the test. Each exercise focuses on a different skill, so using all four will give you a complete practice session.
Also related: English Grammar Exercises Online — a guide to practising grammar with free interactive tools.
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Frequently Asked Questions
What is a relative clause in English?
A relative clause is a subordinate clause that gives more information about a noun or pronoun in the main clause. It is introduced by a relative pronoun such as who, which, that or whose, or by a relative adverb such as where or when. For example: The woman who called you is my colleague. The clause who called you tells us more about which woman is meant. Relative clauses are essential for combining ideas into more sophisticated, fluent sentences.
What is the difference between defining and non-defining relative clauses?
A defining (restrictive) relative clause identifies which specific person or thing is being referred to, and is essential to the meaning of the sentence. No commas are used: The book that I lent you is out of print. A non-defining (non-restrictive) relative clause adds extra information about a noun that is already clearly identified, and is separated by commas: My father, who is a retired teacher, loves gardening. You can remove a non-defining clause without changing the core meaning of the sentence.
When do I use who and when do I use which?
Use who to refer to people: The doctor who treated me was very kind. Use which to refer to things and animals: The report which she submitted was excellent. In defining relative clauses, that can replace both who and which: The doctor that treated me / The report that she submitted. However, in non-defining clauses (with commas), you must use who or which — never that: My brother, who lives in Dublin, is visiting us. (NOT My brother, that lives in Dublin,...)
Can I use that instead of who or which?
Yes, but only in defining relative clauses. In spoken and informal written English, that is very common as a replacement for both who and which: The person that I spoke to was helpful. The film that we watched was boring. However, that cannot be used in non-defining relative clauses (those with commas). It is also generally avoided when the antecedent is a proper noun or when the clause follows a preposition: the city in which I was born (not the city in that I was born).
How is whose used in relative clauses?
Whose is the possessive relative pronoun. It shows that something belongs to or is associated with the noun it refers to. It can refer to both people and things, and is used in both defining and non-defining clauses: The student whose project won the prize received a scholarship. (defining) / The building, whose roof collapsed last winter, is being repaired. (non-defining) Whose always precedes a noun: whose + noun (whose car, whose opinion, whose roof).
When can I omit the relative pronoun?
You can omit the relative pronoun when it acts as the object of the verb in a defining relative clause. This is called a contact clause. For example: The film (that) we watched last night was fantastic. The woman (who/that) I met at the conference has emailed me. The relative pronoun cannot be omitted when it is the subject of the relative clause: The man who called you is at the door. (who cannot be removed here because it is the subject of called.)
Do I need commas with relative clauses?
Yes — commas mark the difference between defining and non-defining relative clauses, and the difference in meaning can be significant. No commas are used with defining clauses: The students who passed the exam celebrated. (Only those who passed celebrated — the clause identifies which students.) Commas are always used with non-defining clauses: The students, who had all studied hard, passed the exam. (All students are referred to — the clause just adds extra information.)
What are relative adverbs and how do they differ from relative pronouns?
Relative adverbs introduce relative clauses that refer to a place, time or reason rather than a person or thing. The main relative adverbs are where (place), when (time) and why (reason). For example: The town where I grew up is on the coast. I remember the year when we first moved abroad. The reason why she resigned is still unclear. In each case, the adverb can be replaced by a preposition + which: the town in which I grew up / the year in which we moved. Relative adverbs are often found in both defining and non-defining clauses.
What are common mistakes with relative clauses?
The most frequent errors include: (1) using that in a non-defining clause: My mother, that is a nurse, ... (should be who); (2) adding an extra pronoun after the relative pronoun: The man who he called ... (remove he); (3) confusing who and which for people and things: The book who I read ... (should be which or that); (4) missing commas in non-defining clauses, or incorrectly adding commas in defining clauses; (5) using whose incorrectly as who's (a contraction of who is): The student whose grade improved (NOT who's grade improved).
Are relative clauses important for IELTS and Cambridge exams?
Yes, very much so. In IELTS Writing Tasks 1 and 2 and in Cambridge B2 First and C1 Advanced writing and speaking, using relative clauses correctly demonstrates grammatical range and accuracy — two key assessment criteria. Examiners look for evidence that candidates can construct complex sentences, and relative clauses are one of the clearest ways to do this. Common exam tasks include sentence-transformation exercises where you must combine two sentences using a relative pronoun, and writing tasks where sophisticated sentence structure is rewarded.