Have you ever wanted to add more detail to a sentence without starting a new one? That’s exactly what relative clauses are for. They let you combine two ideas into one richer, more natural-sounding sentence. Instead of saying “I have a friend. She lives in Rome,” you can say “I have a friend who lives in Rome.” Smoother, isn’t it? In this B1/B2 lesson, we’ll look at relative pronouns, the difference between defining and non-defining clauses, when you can leave the pronoun out, how prepositions behave, reduced forms with -ing and -ed, and the most common mistakes learners make. Stick with me to the end — there’s a 12-question quiz to test what you’ve learnt.
Relative pronouns: the building blocks
Relative pronouns are the small words that link a relative clause to the noun it describes. There are six you need to know:
- who — for people: The teacher who taught me French was Italian.
- which — for things and animals: The book which is on the table is mine.
- that — for people, things or animals (informal): The film that we watched was brilliant.
- where — for places: This is the café where we first met.
- when — for times: I’ll never forget the day when I arrived in Malta.
- whose — for possession: That’s the woman whose dog barks all night.
Notice that whose works for people, things and even animals — it’s the possessive form, regardless of what “owns” the thing.
Defining (restrictive) relative clauses
A defining relative clause gives essential information about the noun. Without it, the sentence doesn’t quite make sense, or you don’t know who or what the speaker is talking about.
Look at this example:
The man who lives next door is a doctor.
If you remove “who lives next door,” you’re left with “The man is a doctor.” Which man? We don’t know. The relative clause is doing important work — it identifies which man we mean.
Three things to remember about defining clauses:
- No commas. The clause is glued to the noun.
- You can use “that” instead of who or which: The man that lives next door…
- They are very common in everyday speech and writing.
Non-defining relative clauses
A non-defining relative clause adds extra information — it’s a kind of bonus. You could remove it and the main sentence would still make perfect sense.
My brother, who lives in London, is visiting next week.
If you take out “who lives in London,” you still know exactly who is visiting — your brother. The clause just adds a detail.
The rules here are different:
- Use commas (or dashes, or brackets) around the clause.
- Don’t use “that” — you must use who, which, where, etc.
- They are more common in writing and slightly more formal speech.
Compare:
- The students who finished early went home. (defining — only the ones who finished early)
- The students, who finished early, went home. (non-defining — all the students finished early, and all went home)
Those commas really do change the meaning.
When you can drop the relative pronoun
Here’s a useful shortcut native speakers use all the time. You can leave out the relative pronoun, but only under two conditions:
- The clause is defining (no commas).
- The pronoun is the object of the clause, not the subject.
Look at these two:
- The book that I read last night was excellent. → The book I read last night was excellent. ✅ (“I” is the subject; “that” is the object)
- The man who lives next door is a doctor. → The man lives next door is a doctor. ❌ (“who” is the subject — you can’t drop it)
A quick test: after the pronoun, is there another subject (I, he, she, we, they, etc.)? If yes, you can usually drop the pronoun. If the verb comes straight after, you must keep it.
Prepositions and relative clauses
This is where things get a bit fancy. When the relative clause includes a preposition, you have two options:
- Formal — preposition before the pronoun: The book about which I spoke is on the shelf.
- Informal — preposition at the end: The book I spoke about is on the shelf.
In everyday English, the informal version is much more natural. You’d hear “the woman I was talking to” far more often than “the woman to whom I was talking.” Save the formal version for academic writing or polished business English.
One rule: if you put the preposition at the front, you must use whom (for people) or which (for things) — never that. So the book about that I spoke is wrong.
Reduced relative clauses with -ing and -ed
You can often shorten a relative clause by dropping the pronoun and the verb “to be,” leaving just an -ing or -ed form. This makes your English sound more fluent.
- The man who is standing there is my uncle. → The man standing there is my uncle.
- The book which was written by Orwell is famous. → The book written by Orwell is famous.
- The students who are studying in the library are quiet. → The students studying in the library are quiet.
Use -ing for active meaning (the man is doing the standing) and -ed (or the past participle) for passive meaning (the book was written by someone). It’s a small change, but it tightens your sentences nicely.
Common mistakes to avoid
Three errors I see all the time in B1/B2 classrooms:
- Using “what” instead of “that” or “which.”
❌ The film what I saw was funny.
✅ The film that I saw was funny.
“What” is not a relative pronoun in standard English — it means “the thing that.” - Double subject.
❌ The man who he lives next door is a doctor.
✅ The man who lives next door is a doctor.
The relative pronoun already replaces the subject — don’t add it twice. - Missing commas in non-defining clauses.
❌ My mother who is a teacher loves reading. (suggests you have more than one mother!)
✅ My mother, who is a teacher, loves reading.
Catch yourself making any of these? You’re not alone — they’re the top three for a reason. The good news is that once you spot the pattern, they’re easy to fix.
Mini quiz: combine the sentences
Combine each pair of sentences using the correct relative pronoun. Decide whether the clause is defining (no commas) or non-defining (with commas). Answers below — no peeking!
- I have a friend. She speaks five languages.
- This is the restaurant. We had dinner there last Friday.
- The novel was a bestseller. It was published in 2010.
- That’s the boy. His sister is in my class.
- I’ll never forget the summer. I learnt to swim that summer.
- The car is very fast. My uncle bought it.
- Mr Smith is retiring. He has worked here for 30 years.
- The hotel was beautiful. We stayed there in Malta.
- The book was fascinating. You lent it to me.
- The woman is a doctor. I was talking to her.
- The film was directed by Nolan. We watched it last night.
- My laptop is broken. I bought it last year.
Answers
- I have a friend who speaks five languages.
- This is the restaurant where we had dinner last Friday.
- The novel, which was published in 2010, was a bestseller.
- That’s the boy whose sister is in my class.
- I’ll never forget the summer when I learnt to swim.
- The car (that/which) my uncle bought is very fast.
- Mr Smith, who has worked here for 30 years, is retiring.
- The hotel where we stayed in Malta was beautiful.
- The book (that) you lent me was fascinating. (pronoun can be dropped — it’s the object)
- The woman (who/whom) I was talking to is a doctor. / The woman to whom I was talking is a doctor.
- The film (that/which) we watched last night was directed by Nolan.
- My laptop, which I bought last year, is broken.
How did you do? If you got 10 or more, you’re well into B2 territory. If a few tripped you up, go back and reread the section that covers them — relative clauses click into place once you’ve practised them out loud.
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