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Unit 19
Relative Clauses (Advanced)
defining, non-defining & reduced
What is a Relative Clause?
A relative clause gives extra information about a noun by joining two ideas into one sentence. It comes directly after the noun it describes and is introduced by a relative pronoun (who, which, that, whose, where, when, why).
Relative Pronouns — Full Reference
| Pronoun | Refers to | Example |
|---|---|---|
| who | People (subject or object) | The man who called is my boss. |
| whom | People (object — formal) | The person whom you met is my teacher. |
| whose | Possession (people or things) | The boy whose bike broke is sad. |
| which | Things or animals | The book which I read was great. |
| that | People or things (defining only) | The car that he drives is fast. |
| where | Places | The café where we met is closed. |
| when | Time | The year when we met was special. |
| why | Reason | The reason why I left was personal. |
Defining vs Non-Defining Clauses
| Aspect | Defining | Non-Defining |
|---|---|---|
| Purpose | Identifies exactly which one — essential | Adds extra information — not essential |
| Commas | ❌ No commas | ✅ Commas before and after |
| "That" | ✅ Can use "that" | ❌ Never use "that" |
| Can omit? | No — meaning changes | Yes — sentence still makes sense |
| Example | The student who studies hard will pass. | My sister, who lives in London, is a designer. |
Omitting the Relative Pronoun
The relative pronoun can be omitted when it is the object of the relative clause — but not when it is the subject.
| Can omit (pronoun = object) | Cannot omit (pronoun = subject) |
|---|---|
| The movie (that) I saw was amazing. | The man who called is my friend. |
| The book (which) she wrote won an award. | The woman who lives next door is a teacher. |
| "I" is the subject here — "that" is the object. | "Who" is performing the action — cannot be removed. |
Reduced Relative Clauses
When the relative pronoun is the subject of the clause, we can shorten (reduce) the clause to a participial phrase.
| Full clause | Reduced clause | Type |
|---|---|---|
| The man who is talking is my boss. | The man talking is my boss. | Active → -ing |
| Students who study hard succeed. | Students studying hard succeed. | Active → -ing |
| The car that was repaired works well. | The car repaired works well. | Passive → past participle |
| The books that were written by her won awards. | The books written by her won awards. | Passive → past participle |
Relative Adverbs — Where, When, Why
Where, when and why act as relative adverbs — they replace prepositional phrases.
- In informal English, when and why can be omitted: The day (when) we met was unforgettable.
| Adverb | Meaning | Example |
|---|---|---|
| where | in / at the place that | The café where we met was cosy. |
| when | at the time that | I remember the day when we first met. |
| why | for the reason that | That's the reason why I left early. |
Prepositions in Relative Clauses
| Informal (preposition at the end) | Formal (preposition + which / whom) |
|---|---|
| The house (that) I grew up in. | The house in which I grew up. |
| The person (who) I spoke to. | The person to whom I spoke. |
| The job (that) she applied for. | The job for which she applied. |
| ⚠ Never: | after a preposition use which (things) or whom (people) |
Which for a Whole Idea · Some of Whom
- , which can refer to the whole previous clause: He passed the exam, which surprised everyone. (not
what surprised/that surprised) - Quantifiers + of whom / of which (non-defining): I have two brothers, both of whom live abroad. · She wrote ten books, most of which are bestsellers.
Annotated Examples
Subject
Verb
Auxiliary
Object
Adjective
Adverb
Preposition
Hover over any word to see its role.
subjectThe studentwhoverbstudies hardverbwill pass.
↳ Defining clause — identifies which student. No commas, "that" possible.
subjectMy sister,who lives in London,verbisobjecta designer.
↳ Non-defining clause — extra info, commas, never "that".
subjectThe manverbtalkingprepositionto Johnverbis my boss.
↳ Reduced clause — "who is talking" reduced to "talking".
Common Mistakes
My sister, that lives in Paris, is happy.
→
My sister, who lives in Paris, is happy.
"That" is never used in non-defining clauses (with commas).
I met a man he is a pilot.
→
I met a man who is a pilot.
Must join with a relative pronoun: who.
That's the reason because I left.
→
That's the reason why I left.
Use "why" to introduce a reason clause, not "because".
The man which lives there is rich.
→
The man who lives there is rich.
"Which" is for things — use "who" for people.
I met the girl who she works at the café.
→
I met the girl who works at the café.
Don't repeat the subject after the relative pronoun.
She was late, what made me angry.
→
She was late, which made me angry.
Referring to the whole idea → , which.
The person to who I spoke was helpful.
→
The person to whom I spoke was helpful.
After a preposition → whom.