Lesson 17
Relative Clauses: Who, Which, That, Whose and Defining Information
This lesson groups five rules that students commonly confuse because they look similar on the surface. Find the antecedent and then test the pronoun's grammatical job. Work through the examples slowly once; speed comes after the pattern is clear.
What you will learn
- Understand and apply: Use 'who' for people and 'which' for things; 'that' can introduce defining clauses.
- Understand and apply: 'Whose' can express possession for people and things.
- Understand and apply: Defining relative clauses normally take no commas.
- Understand and apply: Non-defining relative clauses are set off with commas.
- Understand and apply: 'That' is not normally used in non-defining relative clauses.
For every rule: spot the trigger → identify the grammatical relationship → apply the form → check meaning.
Before you start
Try the warm-up without checking the rule. The purpose is to expose the instinct you currently use, not to score marks.
Which sentence follows the target grammar pattern?
A. The student who asked the question stayed back.
B. The student which asked the question stayed back.
Answer: A. Who commonly refers to people, which to things, and that can refer to people or things in defining clauses.
Rule 1 · G081
Use 'who' for people and 'which' for things; 'that' can introduce defining clauses
Who commonly refers to people, which to things, and that can refer to people or things in defining clauses.
Correct example
The student who asked the question stayed back.
Incorrect example
The student which asked the question stayed back.
Interpretation
Who commonly refers to people, which to things, and that can refer to people or things in defining clauses. In a test, do not memorise this as an isolated sentence. Find the antecedent and then test the pronoun's grammatical job. The correct example shows the pattern in context; compare it directly with the incorrect version and identify the exact word that must change.
Why it matters
Pronoun mistakes create ambiguity or case errors that are easy to miss in long sentences.
Common exam trap
Using a form because it sounds more formal ('between you and I', 'myself') instead of checking case.
How to spot it
Replace the full noun phrase mentally, then ask whether the pronoun is acting as subject, object, possessor or reference word.
3-step solving method
- Find the antecedent.
- Decide the pronoun's job.
- Check case, number and clarity.
Why the incorrect example fails
The target structure requires this rule: Who commonly refers to people, which to things, and that can refer to people or things in defining clauses. In the incorrect version, the repair is to replace “which” with “who”. That is the exact edit a student should be able to justify in an error-spotting question.
Nuance and memory hook
In formal prose, who is often preferred for people. That is not used for a non-defining clause after a comma.
Essential information: no commas.
Quick check
Without relying on what 'sounds right', explain which part of this sentence violates the rule: “The student which asked the question stayed back.”
Reveal quick check answer
Apply Use 'who' for people and 'which' for things; 'that' can introduce defining clauses: Who commonly refers to people, which to things, and that can refer to people or things in defining clauses.
Practice questions
Apply the rule in context
Which sentence is the better choice in standard exam-oriented English?
Explain the error rather than guessing by sound
Why is this sentence problematic in the target rule? “The student which asked the question stayed back.”
Rule 2 · G082
'Whose' can express possession for people and things
Whose introduces a relative clause showing possession and can refer to both people and objects.
Correct example
We chose the plan whose cost was lowest.
Incorrect example
We chose the plan which cost was lowest.
Interpretation
Whose introduces a relative clause showing possession and can refer to both people and objects. In a test, do not memorise this as an isolated sentence. Find the antecedent and then test the pronoun's grammatical job. The correct example shows the pattern in context; compare it directly with the incorrect version and identify the exact word that must change.
Why it matters
Pronoun mistakes create ambiguity or case errors that are easy to miss in long sentences.
Common exam trap
Using a form because it sounds more formal ('between you and I', 'myself') instead of checking case.
How to spot it
Replace the full noun phrase mentally, then ask whether the pronoun is acting as subject, object, possessor or reference word.
3-step solving method
- Find the antecedent.
- Decide the pronoun's job.
- Check case, number and clarity.
Why the incorrect example fails
The target structure requires this rule: Whose introduces a relative clause showing possession and can refer to both people and objects. In the incorrect version, the repair is to replace “which” with “whose”. That is the exact edit a student should be able to justify in an error-spotting question.
Nuance and memory hook
Modern standard English accepts singular 'they' in many contexts. Agreement should remain consistent once that choice is made.
Whose introduces a relative clause showing possession and can refer to both people and objects.
Quick check
Without relying on what 'sounds right', explain which part of this sentence violates the rule: “We chose the plan which cost was lowest.”
Reveal quick check answer
Apply 'Whose' can express possession for people and things: Whose introduces a relative clause showing possession and can refer to both people and objects.
Practice questions
Apply the rule in context
Which sentence is the better choice in standard exam-oriented English?
Explain the error rather than guessing by sound
Why is this sentence problematic in the target rule? “We chose the plan which cost was lowest.”
Rule 3 · G083
Defining relative clauses normally take no commas
A defining clause identifies which person or thing is meant, so it is not normally separated by commas.
Correct example
Students who analyse mocks improve faster.
Incorrect example
Students, who analyse mocks, improve faster, if the clause is essential.
Interpretation
A defining clause identifies which person or thing is meant, so it is not normally separated by commas. In a test, do not memorise this as an isolated sentence. Find the antecedent and then test the pronoun's grammatical job. The correct example shows the pattern in context; compare it directly with the incorrect version and identify the exact word that must change.
Why it matters
Pronoun mistakes create ambiguity or case errors that are easy to miss in long sentences.
Common exam trap
Using a form because it sounds more formal ('between you and I', 'myself') instead of checking case.
How to spot it
Replace the full noun phrase mentally, then ask whether the pronoun is acting as subject, object, possessor or reference word.
3-step solving method
- Find the antecedent.
- Decide the pronoun's job.
- Check case, number and clarity.
Why the incorrect example fails
The target structure requires this rule: A defining clause identifies which person or thing is meant, so it is not normally separated by commas. In the incorrect version, the repair is to replace “Students,” with “Students”; replace “mocks,” with “mocks”; replace “faster, if the clause is essential.” with “faster.”. That is the exact edit a student should be able to justify in an error-spotting question.
Nuance and memory hook
Modern standard English accepts singular 'they' in many contexts. Agreement should remain consistent once that choice is made.
Essential information: no commas.
Quick check
Without relying on what 'sounds right', explain which part of this sentence violates the rule: “Students, who analyse mocks, improve faster, if the clause is essential.”
Reveal quick check answer
Apply Defining relative clauses normally take no commas: A defining clause identifies which person or thing is meant, so it is not normally separated by commas.
Practice questions
Apply the rule in context
Which sentence is the better choice in standard exam-oriented English?
Explain the error rather than guessing by sound
Why is this sentence problematic in the target rule? “Students, who analyse mocks, improve faster, if the clause is essential.”
Rule 4 · G084
Non-defining relative clauses are set off with commas
A non-defining clause adds extra information about an already identified noun and is normally enclosed by commas.
Correct example
My brother, who lives in Pune, is visiting us.
Incorrect example
My brother who lives in Pune is visiting us, if there is only one brother and the information is extra.
Interpretation
A non-defining clause adds extra information about an already identified noun and is normally enclosed by commas. In a test, do not memorise this as an isolated sentence. Find the antecedent and then test the pronoun's grammatical job. The correct example shows the pattern in context; compare it directly with the incorrect version and identify the exact word that must change.
Why it matters
Pronoun mistakes create ambiguity or case errors that are easy to miss in long sentences.
Common exam trap
Using a form because it sounds more formal ('between you and I', 'myself') instead of checking case.
How to spot it
Replace the full noun phrase mentally, then ask whether the pronoun is acting as subject, object, possessor or reference word.
3-step solving method
- Find the antecedent.
- Decide the pronoun's job.
- Check case, number and clarity.
Why the incorrect example fails
The target structure requires this rule: A non-defining clause adds extra information about an already identified noun and is normally enclosed by commas. In the incorrect version, the repair is to replace “brother” with “brother,”; replace “Pune” with “Pune,”; replace “us, if there is only one brother and the information is extra.” with “us.”. That is the exact edit a student should be able to justify in an error-spotting question.
Nuance and memory hook
Modern standard English accepts singular 'they' in many contexts. Agreement should remain consistent once that choice is made.
Essential information: no commas.
Quick check
Without relying on what 'sounds right', explain which part of this sentence violates the rule: “My brother who lives in Pune is visiting us, if there is only one brother and the information is extra.”
Reveal quick check answer
Apply Non-defining relative clauses are set off with commas: A non-defining clause adds extra information about an already identified noun and is normally enclosed by commas.
Practice questions
Apply the rule in context
Which sentence is the better choice in standard exam-oriented English?
Explain the error rather than guessing by sound
Why is this sentence problematic in the target rule? “My brother who lives in Pune is visiting us, if there is only one brother and the information is extra.”
Rule 5 · G085
'That' is not normally used in non-defining relative clauses
Use who or which, not that, in a non-defining relative clause separated by commas.
Correct example
The book, which I bought yesterday, is excellent.
Incorrect example
The book, that I bought yesterday, is excellent.
Interpretation
Use who or which, not that, in a non-defining relative clause separated by commas. In a test, do not memorise this as an isolated sentence. Find the antecedent and then test the pronoun's grammatical job. The correct example shows the pattern in context; compare it directly with the incorrect version and identify the exact word that must change.
Why it matters
Pronoun mistakes create ambiguity or case errors that are easy to miss in long sentences.
Common exam trap
Using a form because it sounds more formal ('between you and I', 'myself') instead of checking case.
How to spot it
Replace the full noun phrase mentally, then ask whether the pronoun is acting as subject, object, possessor or reference word.
3-step solving method
- Find the antecedent.
- Decide the pronoun's job.
- Check case, number and clarity.
Why the incorrect example fails
The target structure requires this rule: Use who or which, not that, in a non-defining relative clause separated by commas. In the incorrect version, the repair is to replace “that” with “which”. That is the exact edit a student should be able to justify in an error-spotting question.
Nuance and memory hook
Modern standard English accepts singular 'they' in many contexts. Agreement should remain consistent once that choice is made.
Essential information: no commas.
Quick check
Without relying on what 'sounds right', explain which part of this sentence violates the rule: “The book, that I bought yesterday, is excellent.”
Reveal quick check answer
Apply 'That' is not normally used in non-defining relative clauses: Use who or which, not that, in a non-defining relative clause separated by commas.
Practice questions
Apply the rule in context
Which sentence is the better choice in standard exam-oriented English?
Explain the error rather than guessing by sound