What a relative clause does
Relative clauses give us more information about someone or something, and let us combine two sentences without repeating information (Cambridge Dictionary, Relative clauses). For example:
I called my aunt, who lives in Cardiff.
Without the relative clause you would need two sentences: "I called my aunt. My aunt lives in Cardiff." The relative clause replaces the repetition.
Relative clauses can also give focus to a person or thing. Compare "This is the film that I told you about" with "I told you about this film".
Choosing the relative pronoun
The relative pronoun depends on what you are referring to (a person, an animal or a thing) and on the type of clause (Cambridge Dictionary, Relative pronouns):
| Pronoun | Used for | Clause type |
|---|---|---|
| who | people and sometimes pet animals | defining and non-defining |
| which | animals and things; a whole sentence | defining and non-defining |
| that | people, animals and things (informal) | defining only |
| whose | possessive meaning, usually people and animals | defining and non-defining |
| whom | people, formal styles or writing, often after a preposition | defining and non-defining |
Who
Who refers to people, and sometimes to pet animals. It introduces both defining and non-defining clauses:
Children who read every day learn new words quickly. (defining)
Our dog Max, who sleeps on my bed, is very old. (non-defining, a pet animal)
Who also works with collective groups of people: We called the police, who came quickly. Do not use who for things: say "There are some good websites which help with grammar", not "websites who help with grammar".
Which
Which refers to animals and things, and it can also refer to a whole sentence. A clause that comments on the whole sentence before it is always introduced with which, and in writing we usually put a comma before it (Cambridge Dictionary, Relative clauses):
The train was late again, which made me angry.
That
That refers to people, animals and things, but only in defining clauses, and it is informal. We do not use that to introduce a non-defining relative clause (Cambridge Dictionary, Relative clauses: defining and non-defining):
My sister, who works in a bank, lives in York.
My sister, that works in a bank, lives in York.
The commas show that the clause is non-defining, so that is not possible.
Whose
Whose shows possession, usually for people and animals, and sometimes for things in formal situations:
I met a woman whose son plays in my football team.
Whom
We use whom in formal styles or in writing, to refer to people when the person is the object of the verb. The most common use of whom is with a preposition (Cambridge Dictionary, Relative pronouns):
The teacher whom we thanked has now retired.
In everyday speech who usually replaces whom.
Find the right pronoun
Choose one answer in each group. The result shows the pronouns that you can use and the Cambridge rule that decides it.
Defining clauses
A defining relative clause tells us which person or thing we mean. It is essential to the meaning, so it takes no commas:
Here is the key that opens the back door.
Tom is a student who asks a lot of questions.
In writing, we do not use commas in defining relative clauses (Cambridge Dictionary, Relative clauses: typical errors). Compare:
Tom is a student who asks a lot of questions.
Tom is a student, who asks a lot of questions.
The clause tells us what kind of student Tom is. This information is essential, so the clause is defining and takes no comma.
Non-defining clauses and commas
A non-defining relative clause adds extra information about a person or thing that is already clear. It describes rather than defines, so in writing we put commas around it (Cambridge Dictionary, Relative clauses: defining and non-defining):
My grandfather, who grew up on a farm, still walks every day.
Our new manager, who comes from Spain, replaces Anna, whose family moved to Canada.
In speaking, we often pause at the beginning and end of the clause instead of using commas.
One comma, two meanings
| Sentence | Meaning |
|---|---|
| His brother, who works at the supermarket, is a friend of mine. | He has only one brother. The clause gives extra information. |
| His brother who works at the supermarket is a friend of mine. | He has more than one brother. The clause tells us which brother. |
This pair comes from Cambridge Dictionary, Relative clauses: defining and non-defining.
Subject or object pronoun
A relative pronoun can be the subject or the object of its clause. This decides whether you can leave it out.
- Subject. I know a man who repairs bikes. (who is the subject of repairs)
- Object. The man who I met yesterday was very kind. (who is the object of met)
In informal styles we often leave out the relative pronoun when it is the object of the clause, as in "the café (that) my parents opened". We only do this in defining clauses (Cambridge Dictionary, Relative pronouns).
Common mistakes
Cambridge Dictionary lists these errors in Relative clauses: typical errors and Relative pronouns.
| Mistake | What happened | Fix |
|---|---|---|
| This is the shop that it sells old books. | Extra subject: the relative pronoun is already the subject, so no personal pronoun. | This is the shop that sells old books. |
| We bought the book that had chosen. | Missing subject: when the relative pronoun is the object, the clause needs its own subject. | We bought the book that Ana had chosen. |
| I watched the film that you told me about it. | Double object: the relative pronoun is the object, so no second object at the end. | I watched the film that you told me about. |
| Tom is a student, who asks a lot of questions. | A defining clause takes no commas in writing. | Tom is a student who asks a lot of questions. |
| My sister, that works in a bank, lives in York. | That cannot introduce a non-defining clause. | My sister, who works in a bank, lives in York. |
| She is the friend on who I depend. | The preposition goes at the end of the clause, not before who. | She is the friend who I depend on. |
Also remember: we do not use what as a relative pronoun. Say "He speaks Spanish and French, which helps him at work". Do not say "He speaks Spanish and French, what helps him at work".
Relative clauses in Cambridge exams
The language specifications of A2 Key and B1 Preliminary list "Relative: who, which, that" in the pronoun section (A2 Key handbook, page 50; B1 Preliminary handbook, page 71).
The glossary of the B1 Preliminary writing mark scheme names relative clauses as a complex grammatical form. It says "Complex grammatical forms: longer and more complex items, e.g. noun clauses, relative and adverb clauses, subordination, passive forms, infinitives, verb patterns, modal forms and tense contrasts." (B1 Preliminary handbook, page 32).
The A2 Key handbook says "A2 Key is targeted at Level A2 on the CEFR." The B1 Preliminary handbook says "B1 Preliminary is targeted at Level B1 on the CEFR." (both on page 3). To see what each level means, read English levels explained.
Try the quiz
Answer the questions in writing first. Then open the answer key.
- Choose who or which: The engineer ___ designed the bridge lives here.
- Add commas if the clause gives extra information, then say why: My brother who lives in Leeds is a nurse. (I have only one brother.)
- Choose who or whom and say which style it is: The managers ___ I consulted agreed.
- Combine into one sentence with a relative clause: We visited my grandmother's village. It is famous for its cheese.
- Find the mistake: The bus that it goes to the airport is late.
- Can you leave out the relative pronoun here? Why (not)? The coat that I bought is too small.
Show all answers
- who. The engineer is a person.
- My brother, who lives in Leeds, is a nurse. The speaker has only one brother, so the clause is extra information. Put a comma before who and a comma after Leeds.
- Formal style or writing: whom ("The managers whom I consulted agreed"). Less formal: who. Whom is rare in conversation.
- We visited my grandmother's village, which is famous for its cheese. (which for a place; comma because it is extra information)
- Remove it: the relative pronoun that is already the subject of the clause.
- Yes. that is the object of bought and the clause is defining, so "The coat I bought is too small" is also correct.
How this lesson was built
The grammar rules and example sentences are adapted from Cambridge Dictionary pages on relative clauses: defining and non-defining, relative clauses, relative pronouns and relative clauses: typical errors, checked on 29 October 2026. The explanations, ordering, exercises and quiz were written for this site.