Grammar guide Updated 2026-09-13
Relative Clauses: How to Teach Who, Which and That
A relative clause adds information about a noun without starting a new sentence: the man who called, the book that I lost. Who, which and that cover almost every case a learner needs, and the difficulty is rarely the choice of word. This guide gives one decision rule, a table of the pronouns, the defining and non-defining contrast, and the mistakes worth correcting first.
Start from the noun, not from the pronoun
Every relative clause answers one question: which person or thing am I talking about? So begin with the noun rather than the pronoun. A person takes who; a thing takes which or that. The teacher who helped me and the bus that stops here are both built from the same pattern, and there is no exception worth teaching before this one is automatic.
The second decision matters more than the first: can the clause be left out? If it can, it is a non-defining clause and takes commas; if it cannot, it is defining and takes no commas. Decide that before you choose between which and that, because the comma rule limits the choice.
Who, which and that in one table
| What it refers to | Type | Pronoun | Example |
|---|---|---|---|
| A person | defining | who or that | The teacher who helped me left. |
| A thing | defining | which or that | The bus that stops here is late. |
| A person | non-defining | who only | My sister, who lives in Leeds, called. |
| A thing | non-defining | which only | The bus, which stops here, is late. |
| Possession | either | whose | The student whose answer was best won. |
| A place or time | either | where or when | The town where I grew up is small. |
Defining and non-defining clauses
A defining clause tells the listener which one. Remove it and the sentence either breaks or changes meaning: The woman who teaches my class is on holiday is about one particular teacher, and The woman is on holiday is about somebody the listener cannot identify yet.
A non-defining clause adds a comment that the sentence does not need: My sister, who lives in Leeds, called last night. The clause sits between commas and the sentence stands without it. In speech the distinction is carried by a pause, so read the two versions aloud before asking learners to punctuate them. Two consequences follow, and both are worth drilling. First, a non-defining clause never uses that. Second, a non-defining clause should not be used to say something the listener needs in order to identify the noun, or the meaning becomes unclear.
What happens to the object pronoun
When the relative pronoun is the object of its own clause, English drops it in defining clauses: the book I bought equals the book that I bought. The example below uses the same noun twice, once with the pronoun and once without.
Learners often over-correct here and put the pronoun back inside the clause: the film that we saw it is wrong, because that has already done the job of the object. The omission is optional in defining clauses and impossible in non-defining clauses, where the pronoun must stay: My car, which I bought in May, is already noisy.
The mistakes that repeat most
- That in a non-defining clause. My car, that is old, breaks down weekly becomes My car, which is old, breaks down weekly.
- The object said twice. The film that we saw it was long loses the second pronoun: The film that we saw was long.
- Who for things. The shop who sells bread should be the shop that sells bread or the shop which sells bread.
- The verb left out. The man who in the garden needs a verb: the man who is in the garden.
- Whose and who's confused. Whose shows possession, as in the girl whose bag was lost; who's is short for who is.
- Inverted word order. The relative clause keeps statement order, so the town where lives my aunt should be the town where my aunt lives.
A teaching sequence that works
Six steps, one lesson each, moving from joining two sentences to choosing freely between the pronouns.
| Step | Teacher shows | Learners do |
|---|---|---|
| 1 | I met a man. He was a pilot. | Underline the repeated noun in both sentences. |
| 2 | I met a man who was a pilot. | Join three pairs with person nouns. |
| 3 | I bought a book. It was cheap. | Join three pairs with thing nouns and which. |
| 4 | One comma pair and one plain pair side by side. | Mark each sentence defining or non-defining. |
| 5 | The same sentence with who, which and that. | Choose the pronoun on ten items and say why. |
| 6 | The book that I bought and the book I bought. | Rewrite six sentences with the object pronoun left out. |
Practice that makes the pattern automatic
Relative clauses are easy to understand on the page and hard to produce at speed, because three decisions have to happen at once: person or thing, defining or not, pronoun present or dropped. A short drill separates those decisions, and a mixed review puts them back together with the tenses learners already know.
Keep the first lessons inside vocabulary the class already owns. A relative clause built from words learners have to look up tests two skills at once, and the grammar disappears behind the vocabulary, so reuse the nouns, jobs and objects from the previous unit wherever you can.
Use the grammar drills for the pronoun choice, then the mixed review or the timed challenge to test the same forms against the clock. For class use, print the same sentences as a worksheet with an answer key or build your own set in the worksheet builder. The subject-verb agreement guide covers the verb ending inside the clause, and the question forms guide handles the word order that learners invert here.
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Frequently asked questions
When should I use who, which or that?
Use who for people and which or that for things. In a defining clause, that and which are both correct for a thing, and who is preferred for a person, especially in writing. In a non-defining clause with commas, use who for people and which for things, and never that.
What is the difference between a defining and a non-defining clause?
A defining clause tells the listener which person or thing you mean, so the sentence needs it: the woman who teaches my class. A non-defining clause adds extra information and could be removed: my sister, who lives in Leeds, called. Defining clauses take no commas; non-defining clauses sit between commas.
Can I leave out the relative pronoun?
Yes, when the pronoun is the object of the clause and the clause is defining: the book I bought is the same as the book that I bought. You cannot leave it out when the pronoun is the subject, as in the man who called, and you cannot leave it out in a non-defining clause.
Why is my car, that is old, wrong?
Because that cannot be used in a non-defining clause. Once the clause sits between commas it is added information, and English uses which for things and who for people in that position. The correct sentence is my car, which is old, breaks down weekly.
What is the fastest way to teach relative clauses?
Start from two short sentences that share a noun, then join them with who for people and which for things, and let learners see the compression for themselves. Add the comma contrast in the next lesson, then that, then the dropped object pronoun. Four short steps beat one long explanation.
Keep reading
Every guide on this blog is paired with a free drill: the same rules, applied question by question, with explanations and a printable worksheet.