- Who and that are used for people.
- That and which are used for things.
- Which cannot be used for people.
To understand when to use them in a sentence we should understand relative clauses.
What are relative clauses
A relative clause is a sentence within a sentence which is related to the main sentence.
I like the woman who lives next door.
The main sentence: I like the woman
The relative clause: who lives next door
Whether we use ‘who’, ‘that’, or ‘which’ depends on the type of a relative clause: defining or non-defining.
| Defining Relative clauses | Non-Defining Relative clauses |
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| I like the woman who lives next door. If we take out ‘who lives next door’ from this sentence, it won’t make any sense: “I like the woman.” | He lives in London, which is the capital of the UK. If we take out ‘which is the capital of the UK’ the sentence will still make sense: “He lives in London.”
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How to use ‘which’, ‘who’ and ‘that’ in relative clauses
- Which, that and who can be used in defining and non-defining relative clauses.
- That cannot be used in non-defining clauses.
❌He lives in London, that is the capital of the UK.
When can we omit that/who/which
We can omit that/who/which if it’s in a defining clause and it’s not a subject.
Compare:
| Can omit | Can’t omit |
| She likes the book that I bought her. That is not a subject, so we can omit it: She likes the book I bought her. | I need a secretary who can type quickly.
Who – is a subject in the sentence “Who can type quickly”, so we can’t omit it. |
We can’t omit which in a non-defining clause.
| My boss, who is Nigerian, lives in Cape Town. Who is the subject in “who is Nigerian” and we can’t omit it. | Last month I bought a new dress, which I don’t like now. Which is not a subject but we still can’t omit it. |
If it’s clear, take the quiz to strengthen your knowledge.
My Multiple Choice Quiz
Practice more with these exercises.
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References:
Who, Which, That: The Blue Book of Grammar
Perfect English: Relative Clauses
English Grammar in Use by Raymond Murphy
