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Relative clauses are the structures that allow you to build complex, information-rich sentences in English. Instead of writing "I met a woman. The woman speaks six languages," you can write "I met a woman who speaks six languages." That embedded clause is a relative clause, and mastering it is essential for fluent, connected English at B1 level and above. This guide covers everything — from basic who/which/that choices to reduced participial phrases and the most common mistakes.
1. What Are Relative Clauses?
A relative clause is a subordinate clause that modifies (gives more information about) a noun or pronoun in the main clause. It is attached directly after the noun it refers to and is introduced by a relative pronoun or relative adverb.
The teacher who taught me grammar was very patient.
The book that I borrowed from the library was fascinating.
The city where I was born is in the south of France.
In each example, the bold portion is the relative clause. It tells us which teacher, which book, and which city we are talking about.
2. Relative Pronouns and Adverbs
The choice of relative pronoun or adverb depends on what the noun it refers to represents:
| Pronoun/Adverb | Refers to | Example |
|---|---|---|
| who | People (and named animals) | The doctor who treated me was very kind. |
| which | Things, animals, ideas | The film which won the award was brilliant. |
| that | People or things (defining only) | The car that I bought needs a service. |
| whose | Possession (people or things) | The student whose essay won is in my class. |
| where | Places | The village where I grew up is tiny. |
| when | Times | I remember the year when we met. |
| why | Reasons (after "reason") | The reason why she left is unclear. |
3. Defining Relative Clauses
A defining relative clause (also called a restrictive relative clause) identifies which person or thing we mean. The information in the clause is essential — without it, the sentence either does not make sense or has a completely different meaning.
Key features of defining relative clauses:
- No commas separate it from the main clause.
- You can use that, who, or which.
- You can omit the pronoun when it is the object of the clause.
The man who called me was a journalist. (defines which man)
The report that I submitted received excellent feedback. (defines which report)
Is this the book which you recommended? (defines which book)
Omitting the Relative Pronoun
In defining relative clauses, you can omit the relative pronoun when it acts as the object of the clause — that is, when it is not the subject performing the action:
The book that I read was excellent. → The book I read was excellent. (omit — "I" is the subject, "that/the book" is the object)
The man who called me was a journalist. (cannot omit — "who/the man" is the subject performing the calling)
Ask: who is performing the action in the relative clause? If it is the noun the clause modifies, you cannot omit. If someone else is performing the action on the noun, you can omit.
4. Non-Defining Relative Clauses
A non-defining relative clause (also called a non-restrictive relative clause) adds extra information about a noun that is already clearly identified. The noun could be a unique person (a proper name), or the context already makes it clear which one is meant.
Key features of non-defining relative clauses:
- Commas (or dashes) enclose the clause — one before, one after (if the clause is mid-sentence).
- Never use "that" — use who or which.
- Cannot omit the relative pronoun.
- The clause can be removed without changing the core meaning of the sentence.
My sister, who lives in Berlin, is visiting us next week.
The Eiffel Tower, which was built in 1889, attracts millions of visitors annually.
Professor Kim, whose research I have been following, will speak at the conference.
Last summer, when we visited Lisbon, the weather was perfect.
Compare these two sentences — the comma makes a crucial difference:
Students who work hard will pass the exam. (defining — not all students, only hard-working ones)
The students, who work hard, will pass the exam. (non-defining — all students work hard; this is extra information)
5. When to Use who vs which vs that
This is the question most learners ask. Here are the three governing rules:
- who — always for people. "The woman who won the award gave a short speech."
- which — for things and animals (and always in non-defining clauses). "The proposal, which took three weeks to write, was accepted."
- that — only in defining clauses; can replace both who (people) and which (things) in informal and spoken English. "The email that I sent bounced back." / "The colleague that helped me is now retired."
Never use "that" in a non-defining relative clause:
✗ My father, that is a doctor, lives in Edinburgh.
✓ My father, who is a doctor, lives in Edinburgh.
6. The Zero Relative Pronoun (Contact Clause)
When a relative pronoun is omitted from a defining clause, the result is called a contact clause or zero relative. This is extremely common in spoken and informal written English.
The film that we saw last week was incredible.
The film (that) we saw last week was incredible. (zero relative — "that" omitted)
The film we saw last week was incredible. (final form)
Other examples of the zero relative:
- The hotel (that) we stayed at was very comfortable.
- The man (who/that) I spoke to yesterday was very helpful.
- Is this the coffee shop (where/that) you met her?
7. Reduced Relative Clauses (Participial Phrases)
A full relative clause can often be reduced to a shorter participial phrase. This makes sentences more concise and formal. There are two types:
Active Reduced Clause (present participle -ing)
When the relative pronoun is the subject of an active verb, replace "who/which + is/are + -ing verb" with just the -ing form:
The woman who is standing by the door is my manager.
The woman standing by the door is my manager.
The students who are waiting outside should come in.
The students waiting outside should come in.
Passive Reduced Clause (past participle)
When the relative clause is passive, remove the relative pronoun and the auxiliary "be":
The car which was stolen last night has been found.
The car stolen last night has been found.
Any items that are left in the office will be discarded.
Any items left in the office will be discarded.
8. Whose: Possessive Relative Clauses
Whose is the possessive form of who. It replaces a possessive adjective (his, her, its, their) and connects to a noun. It is used for both people and things:
The scientist whose discovery changed medicine died in poverty.
The house whose windows were broken has now been repaired.
She is the author whose novel I've been reading.
whose (relative pronoun — possession) vs who's (contraction of "who is" or "who has")
✗ The student who's book was stolen reported it immediately.
✓ The student whose book was stolen reported it immediately.
9. Common Mistakes with Relative Clauses
Here are the errors that appear most frequently in learner writing, with corrections:
| Mistake | Wrong | Correct |
|---|---|---|
| Using "that" in non-defining clause | My mother, that is a nurse, works nights. | My mother, who is a nurse, works nights. |
| Missing comma in non-defining clause | London which is the capital has millions of visitors. | London, which is the capital, has millions of visitors. |
| Using "which" for people | The man which I met yesterday was interesting. | The man who/that I met yesterday was interesting. |
| Confusing whose/who's | The writer who's books I love is on tour. | The writer whose books I love is on tour. |
| Double subject | The student who she won the prize is my friend. | The student who won the prize is my friend. |
| Omitting pronoun in subject position | The man ___ called me was a journalist. | The man who called me was a journalist. |
10. Sentence-Combining Practice
One of the most effective ways to master relative clauses is sentence combining — taking two short sentences and joining them into one with a relative clause:
Simple sentences: I read a book. The book won the Booker Prize.
With relative clause: I read a book that/which won the Booker Prize.
Zero relative: I read a book (that) won the Booker Prize. (cannot omit — subject position)
Simple sentences: She met a professor. The professor's research focuses on climate change.
With relative clause: She met a professor whose research focuses on climate change.
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