Relative Clauses

Relative clauses (also called adjective clauses) are one of the most powerful tools in English for adding detail and precision to your writing. They allow you to identify which person or thing you mean, or to provide extra information about someone or something. This A2–B2 lesson covers both defining and non-defining relative clauses with exercises and answers. You'll master all relative pronouns (who, which, that, whose, where, when, whom) through clear explanations and online practice.

To use relative clauses correctly, you need to understand 2 Types, 2 Functions, and 1 Critical Rule:

• 2 Types: Defining clauses (essential information, no commas) vs Non-defining clauses (extra information, with commas)
• 2 Functions: Subject clauses (pronoun cannot be omitted) vs Object clauses (pronoun can be omitted in defining clauses)
• 1 Critical Rule: Non-defining clauses NEVER use 'that' — only 'who' and 'which'

The biggest challenge? Knowing when you can omit the relative pronoun (the "zero relative") and understanding why 'that' disappears in non-defining clauses. This lesson follows a clear progression: we'll first focus on defining relative clauses (Sets 1–4), where you'll learn the core pronouns (who, which, that, where) and omission rules. Then we'll introduce non-defining clauses (Sets 5–6), which follow different punctuation and pronoun rules. Finally, you'll practice comparing both types with mixed defining and non defining relative clauses exercises (Set 7).

Defining Clauses: Who, Which & That

A defining relative clause (also called a restrictive clause) gives essential information about a noun. It tells us exactly which person or thing we mean. Without this information, the sentence would be unclear or incomplete.

The Core Pronouns

Key Rules

1. For people: Use who or that (who is more common in formal English)

• The teacher who helped me pass the exam was very patient.
• I have a friend that speaks five languages.

2. For things: Use which or that (that is more common in informal English)

• The film which we watched last night was boring.
• The laptop that I use for work is very old.

3. No commas: Defining clauses are NOT separated by commas. The clause is essential to identify the noun.

• ✅ The man who called you has left a message. (Which man? The one who called.)
• ❌ The man**,** who called you**,** has left a message. (This changes the meaning — see non-defining clauses below.)

When to Use Defining Clauses

Use defining relative clauses when the information is necessary to identify which person or thing you're talking about:

• "The woman who lives next door" — tells us which woman (not just any woman)
• "The restaurant that opened last month" — identifies which restaurant (not all restaurants)

Without the clause, the sentence would be too vague: "The woman is a doctor" (which woman?).

👉 Practice Who, Which & That →

Extending Pronouns: Where, When & Whose

Beyond who, which, and that, we have three more relative pronouns that add specific information about place, time, and possession.

The Extended Pronouns

Where (Places)

Use where to talk about places. It replaces a preposition + which:

• The hotel where we stayed was excellent. (= in which we stayed)
• This is the town where Shakespeare was born. (= in which Shakespeare was born)

When (Times)

Use when to talk about times. It replaces a preposition + which:

• Do you remember the summer when it rained every day? (= in which it rained)
• That was the year when I graduated. (= in which I graduated)

Note: 'When' is often omitted in informal English: "That was the year I graduated."

Whose (Possession)

Use whose to show possession. It's the relative form of 'who' and replaces his/her/their:

• The man whose car was stolen reported it to the police. (his car was stolen)
• I know a girl whose mother is a famous singer. (her mother is a famous singer)

Important: Don't confuse 'whose' (possession) with 'who's' (= who is).

Relative Pronouns vs Relative Adverbs

It's useful to understand the difference:

Don't Confuse: Relative 'Where/When' vs Indirect Questions

Relative clauses modify a noun and tell us which one:

• The place where I live is very quiet. (which place? the one where I live)

Indirect questions are embedded questions (usually after verbs like know, ask, wonder):

• I don't know where I left my keys. (embedded question: Where did I leave my keys?)

The key difference: Relative clauses need a noun to modify ("the place"), while indirect questions don't.

👉 Practice Where, When & Whose →

Subject vs Object: The Omission Rule

This is THE KEY to understanding when you can omit a relative pronoun (the "zero relative"). The rule depends on whether the pronoun is the subject or object of the relative clause.

Subject Relative Clauses

When the relative pronoun is the subject of the clause (it performs the action), you CANNOT omit it:

Important: The term "subject" here refers to the pronoun's role in the relative clause, not whether it's a subject pronoun like 'I' or 'he'. We're asking: "Is the pronoun the subject of the verb in the relative clause?"

Object Relative Clauses

When the relative pronoun is the object of the clause (the action is done to it), you CAN omit it in defining clauses:

How to Identify Subject vs Object

Quick test: Look at the verb in the relative clause. Does it have a subject already?

If NO subject after the pronoun → The pronoun is the subject → Cannot omit:

• The woman who ___ answered the phone... (who answered — no other subject)

If there IS a subject after the pronoun → The pronoun is the object → Can omit:

• The email that ___ you sent... (you sent it — 'you' is the subject, 'that' is the object)

Common Patterns

Subject clauses (pronoun cannot be omitted):

• who/which/that + verb
• The bird that is sitting on the fence...
• The man who works here...

Object clauses (pronoun can be omitted):

• who/which/that + subject + verb
• The novel (which) his friend recommended...
• The programme (that) everyone is talking about...

Why This Matters

Omitting the object pronoun (zero relative) is extremely common in spoken English and makes your speech sound more natural:

• Formal: "The book which I read last week was excellent."
• Natural: "The book I read last week was excellent."

But never try to omit a subject pronoun — it creates an error:

• ❌ "The man called you has left a message." (Missing 'who')
• ✅ "The man who called you has left a message."

👉 Practice Subject vs Object Clauses →

Formal Defining Clauses: Whom & Prepositions

At B2 level and in formal writing, you'll encounter whom and preposition + relative pronoun structures.

Whom: The Object Form of 'Who'

Whom is the object form of 'who', used for people when the pronoun is the object of the verb or preposition. It's mainly used in formal English.

Informal (common):

• The man who I spoke to was very helpful.
• The man that I spoke to was very helpful.
• The man I spoke to was very helpful. (zero relative)

Formal:

• The man to whom I spoke was very helpful.
• The colleague with whom I worked has retired.

Preposition Placement

When a relative clause contains a preposition, you have two options:

1. Preposition at the end (informal, common in spoken English):

• The company which I work for is expanding.
• The people who she was talking to left early.
• The house (that) we were looking at was too expensive.

2. Preposition before the relative pronoun (formal, common in written English):

• The company for which I work is expanding.
• The people to whom she was talking left early.
• The house at which we were looking was too expensive.

Rules for Preposition + Relative Pronoun

Note: When the preposition comes before the pronoun:

• Use whom (not 'who') for people
• Use which (not 'that') for things
• You cannot omit the pronoun
• You cannot use 'that'

Examples in Context

In modern English, the informal structure (preposition at the end) is far more common in everyday speech and writing. The formal structure is mainly found in academic writing, legal documents, and very formal contexts.

👉 Practice Whom & Prepositions →

Non-defining Clauses: Commas & Restrictions

Now we introduce a completely different type of relative clause: non-defining clauses (also called non-restrictive clauses). Everything you've learned so far applies to defining clauses. Non-defining clauses follow different rules.

What Are Non-defining Clauses?

Non-defining clauses give extra information about a noun that is already clearly identified. The information is not essential to understand which person or thing we mean. If you remove the clause, the sentence still makes complete sense.

The Three Big Differences

Comma Rules

Non-defining clauses are always separated from the main clause by commas:

Defining (no commas):

• My sister who lives in Paris is coming to visit. (I have more than one sister; the clause tells us which one)

Non-defining (with commas):

• My sister**,** who lives in Paris, is coming to visit. (I have only one sister; the clause adds extra information about her)

Note: In non-defining clauses, the clause is like a parenthesis — it could be removed without changing the basic meaning: "My sister is coming to visit."

Pronouns in Non-defining Clauses

Use who for people and which for things. Never use 'that':

People:

• Our neighbour**,** who is 85 years old**,** still goes jogging every morning.
• Professor Clark**,** who I studied under at university**,** has retired.

Things:

• The Eiffel Tower**,** which was built in 1889**,** is in Paris.
• This painting**,** which is worth millions**,** was donated to the gallery.

⚠️ The Non-defining 'That' Ban

This is the #1 error students make with non-defining clauses: trying to use 'that'.

Why students make this mistake: In defining clauses, 'that' works perfectly for both people and things. It's natural to assume it works everywhere. But it doesn't.

The rule is absolute: 'That' cannot be used in non-defining clauses. Ever.

Why this rule exists: Historically, 'that' has always been reserved for defining (restrictive) clauses in English grammar. Non-defining clauses, which provide supplementary information, require 'who' or 'which'. This distinction has been a feature of English grammar since Middle English, and it helps maintain clarity in writing.

Memory trick: Commas = no 'that'. If you see commas around a relative clause, 'that' is banned.

Omission Rules in Non-defining Clauses

Unlike defining clauses, you cannot omit the relative pronoun in non-defining clauses, even when it's the object:

Defining clause (object pronoun can be omitted):

• The film (that) we watched was boring. ✅

Non-defining clause (object pronoun cannot be omitted):

• Professor Clark**,** who I studied under at university**,** has retired. ✅
• ❌ Professor Clark**,** I studied under at university**,** has retired. (Missing 'who')

Meaning Difference: Defining vs Non-defining

The same sentence with and without commas can have different meanings:

Defining (no commas):

• I have three sisters. My sister who lives in Paris is coming to visit.
  • Meaning: The clause identifies which sister (the one in Paris, not the others).

Non-defining (with commas):

• I have one sister. My sister**,** who lives in Paris, is coming to visit.
  • Meaning: The clause adds extra information. There's only one sister, so no need to identify which one.

When to Use Non-defining Clauses

Use non-defining clauses when:

1. The noun is already fully identified (proper names, unique things, possessive pronouns)

   • My mother, who is 60, still works full-time. (only one mother)
   • The Eiffel Tower, which was built in 1889, is in Paris. (unique landmark)
   • Our house, which we bought in 2010, needs repairs. (already identified by "our")

2. You want to add extra, non-essential information

   • She married John**,** who she met at university.
   • I visited Rome**,** which is the capital of Italy.

👉 Practice Non-defining Clauses →

Advanced Non-defining: Which for Whole Clauses

At B2 level, there's a special advanced use of 'which': referring to an entire clause or situation, not just a single noun.

Which Referring to a Whole Clause

When 'which' appears at the start of a non-defining clause and refers back to the whole previous clause (not just the noun before it), it means "and this" or "which fact":

Examples:

• She passed the exam**,** which surprised everyone.

  • 'Which' = the fact that she passed (not just "the exam")
  • Meaning: She passed the exam, and this surprised everyone.

• He never apologised**,** which made me angry.

  • 'Which' = the fact that he never apologised
  • Meaning: He never apologised, and that made me angry.

• The meeting was cancelled**,** which was a relief.

  • 'Which' = the fact that the meeting was cancelled
  • Meaning: The meeting was cancelled, and this was a relief.

How to Identify This Pattern

Question to ask: Does 'which' replace a noun or a whole idea?

Replacing a noun (standard non-defining):

• My car**,** which is ten years old**,** still runs well.
  • 'Which' refers to "my car" (the noun)

Replacing a whole clause (advanced):

• My car broke down again**,** which was very annoying.
  • 'Which' refers to "my car broke down again" (the whole situation)

Why This Matters

This construction is very common in both spoken and written English when you want to add a comment or reaction to a whole situation:

• They've decided to move to Australia**,** which is a big change.
• He quit his job without another one lined up**,** which seemed risky.
• The train was delayed by two hours**,** which meant I missed my connection.

Note: This use of 'which' is always non-defining (with a comma) and always comes after a comma at the end of the main clause.

Additional Pronouns in Formal Non-defining Clauses

In formal non-defining clauses, you can also use:

Whom (object form of 'who'):

• The CEO**,** with whom I discussed the proposal**,** agreed to the changes.
• Her parents**,** both of whom were teachers**,** encouraged her to study.

Where, when (for places and times):

• We visited Paris**,** where we spent a week sightseeing.
• I graduated in 2020**,** when the pandemic started.

Whose (possession):

• My colleague**,** whose office is next to mine**,** has resigned.
• The author**,** whose books I love**,** is giving a talk tonight.

All these follow the same non-defining rules: commas required, pronouns cannot be omitted, 'that' not allowed.

👉 Practice Which for Whole Clauses →

Defining vs Non-defining: Comparison

Now that you've learned both types, let's compare them directly. Understanding the differences is crucial for B2-level accuracy.

Side-by-Side Comparison

Meaning Differences

The same sentence structure can have different meanings:

1. Students who were late were not allowed in.

• Defining (no commas): Only the students who were late were not allowed in. (Others were allowed in.)

1. Students, who were late, were not allowed in.

• Non-defining (with commas): All the students were late, and none were allowed in. (The clause adds information about all students.)

2. My brother who lives in London is a lawyer.

• Defining: I have more than one brother. The one in London is a lawyer. (Others may have different jobs.)

2. My brother, who lives in London, is a lawyer.

• Non-defining: I have one brother. He lives in London and is a lawyer. (One person, two facts.)

Decision Tree: Which Type to Use?

Ask yourself these questions:

1. Is the noun already clearly identified?

• ✅ YES → Probably non-defining
  • Proper names: London, which is the capital...
  • Possessives: My mother, who is 60...
  • Only one: The sun, which is a star...
• ❌ NO → Probably defining
  • The city where I was born... (which city?)

2. Can I remove the clause and still know who/what we're talking about?

• ✅ YES → Non-defining (use commas)
  • Shakespeare**,** who was born in 1564**,** wrote many plays. (We know who Shakespeare is.)
• ❌ NO → Defining (no commas)
  • The playwright who wrote Hamlet was Shakespeare. (The clause identifies which playwright.)

3. Do I need the information to identify the noun, or am I just adding interesting details?

• Identify → Defining (no commas)
  • People who live in glass houses shouldn't throw stones. (Which people specifically?)
• Add details → Non-defining (commas)
  • My neighbour**,** who lives in a glass house**,** is very careful. (Just extra info about the neighbour.)

Practical Examples

Let's practice choosing:

Scenario 1: You have one car. It's red. You want to mention this.

• ✅ "My car**,** which is red**,** needs washing." (Non-defining — you have one car, just adding a detail)
• ❌ "My car which is red needs washing." (Implies you have multiple cars)

Scenario 2: You have three cars (red, blue, black). You want to say which one needs washing.

• ✅ "The car which is red needs washing." or "My red car needs washing." (Defining — identifies which car)
• ❌ "The car, which is red, needs washing." (Implies you're talking about all cars or one specific car already known)

Scenario 3: Talking about your only sister.

• ✅ "My sister**,** who lives in Tokyo**,** is visiting." (Non-defining — only one sister)

Scenario 4: You have two sisters. One lives in Tokyo, one in Paris.

• ✅ "My sister who lives in Tokyo is visiting." (Defining — identifies which sister)

Common Errors in Mixed Practice

👉 Practice Mixed: Defining vs Non-defining →

Common Mistakes to Avoid

Quick Summary

The Framework: 2 Types, 2 Functions, 1 Critical Rule

5-Step Transformation Process: Combining Sentences

When you want to combine two sentences using a relative clause:

Example: "I met a woman." + "She speaks six languages."

Step 1: Identify the Common Element

• Find the noun that appears in both sentences
• Here: "a woman" = "She"

Step 2: Determine the Clause Type

• Is the information essential to identify the noun? → Defining (no commas)
• Is the noun already identified and you're just adding extra info? → Non-defining (add commas)
• Here: Essential info (identifies which woman) → Defining

Step 3: Choose the Relative Pronoun

• People: who/that (defining) or who (non-defining)
• Things: which/that (defining) or which (non-defining)
• Possession: whose
• Place: where
• Time: when
• Here: People → who or that

Step 4: Check the Pronoun's Role

• Is the pronoun the subject of the relative clause? → Keep the pronoun
• Is the pronoun the object of the relative clause (and it's defining)? → Can omit
• Here: "who speaks" — subject → Keep it

Step 5: Position the Clause

• Place immediately after the noun it modifies
• Result: "I met a woman who speaks six languages."

Omission Rules Summary

Pronoun Quick Reference

The Critical Rule: Non-defining 'That' Ban

Never use 'that' in non-defining clauses

• ❌ My mother**,** that is 60**,** works full-time.
• ✅ My mother**,** who is 60**,** works full-time.

Memory trick: Commas = no 'that'

Practice Tips

1. Identify the clause type first: Before choosing a pronoun, ask: "Is this information essential (defining) or extra (non-defining)?" This determines commas and whether 'that' is allowed.

2. Check subject vs object before omitting: Never assume you can drop a pronoun. Ask: "Is the pronoun the subject of the relative clause verb?" If yes, you must keep it.

3. Remember the 'that' ban is absolute: If you see commas around a relative clause, 'that' is never correct. Use 'who' (people) or 'which' (things).

4. Practice combining sentences: Take two simple sentences and practice turning them into one with a relative clause. This builds intuition for clause structure.

5. Read examples aloud: Pay attention to the natural pause (comma) in non-defining clauses. This helps internalize when commas are needed.

6. Watch for proper names and possessives: These almost always take non-defining clauses (with commas): "London, which...", "My mother, who...", "The President, who..."

Practice All Exercises

Ready to practice everything you've learned? These relative clauses exercises are available as multiple choice questions with answers and online worksheets. Work through the sets in order — they follow the same progression as this lesson:

👉 Start with Set 7: Defining vs Non-defining Mixed Practice for a comprehensive review of all relative clauses!