Who, Which or That? Relative Clauses Made Clear

You often need to say more about a noun without starting a new sentence. A relative clause lets you do that. You attach the extra information right after the noun it describes.

Take the noun my neighbour. You could write two short sentences. My neighbour is a nurse. She works nights. Or you can join them. My neighbour who works nights is a nurse. The second version is smoother and it shows exactly which noun you mean.

Most of your choices come down to three habits. Pick who, which or that for the noun in front of you. Decide if the clause identifies that noun or only adds a side detail. Then keep the pronoun or drop it when the grammar allows it. Once you can do those three things, the rest is polish.

Add detail without starting a new sentence

A relative clause is a small clause that follows a noun and describes it. It starts with a relative pronoun such as who, which, that, whose, or a relative adverb such as where and when. The main clause still carries the main message.

Look at the pattern in a sentence you would actually say. I lost the keys that you gave me. The main message is I lost the keys. The clause that you gave me tells your listener which keys you mean. You did not need a second sentence.

You use the same pattern for people, things, places and times. She is the teacher who helped me. This is the cafe where we met. Monday is the day when I am free. In each case the clause sits right after the noun it explains [1].

Use who for people, which for things

You choose the pronoun by looking at the noun in front of the clause. Use who for people. Use which for things and animals. Use that for either one, but only when the clause identifies the noun.

Say both versions out loud and feel the difference. The doctor who treated me was kind. The hospital which treated me was clean. You would not swap them. The doctor which treated me sounds wrong to most listeners. The hospital who treated me sounds wrong too.

That is flexible in one context. The film that we saw was long means the same as The film which we saw was long. Both are correct in a defining clause. American style guides prefer that here, while British exams accept both forms.

Commas tell if you identify or add

This split decides your commas. A defining clause identifies which one you mean. It takes no commas. A non-defining clause adds a detail you could drop. It sits inside commas, or after one comma at the end.

Compare the meaning, not just the punctuation. My sister who lives in Leeds is visiting suggests you have more than one sister, and you point to the one in Leeds. My sister, who lives in Leeds, is visiting suggests you have one sister, and you add where she lives as extra news. Your listener hears a different family.

That cannot open a non-defining clause. You can say My car, which is old, still runs. You cannot say My car, that is old, still runs. If you see commas, choose who, which, whose, where or when. Keep that for sentences with no commas.

Drop the pronoun when it is the object

You can leave the pronoun out only when it is the object of its own clause. Test this by finding the subject inside the clause. If the clause already has its own subject, you can drop who, which or that.

Take the book I read. The clause is I read. It already has the subject I, so the missing pronoun is the object. You can also keep it. The book that I read means the same and sounds a little more formal.

Now take the book that fell. The clause is that fell. It has no other subject, so that is the subject. You cannot drop it. The book fell would change the structure and lose the link to the first noun.

Show possession, place and time

You need three more links for common sentences. Use whose for possession. Use where for place. Use when for time. They work in both defining and non-defining clauses, with the same comma rule you already know.

Whose can refer to people, and often to things in formal writing. That is the student whose bike was stolen. It is a company whose rules are strict. You do not change whose for singular or plural. The noun after it decides the rest of the clause.

Where and when replace a longer phrase with a preposition. This is the house where I grew up is more natural than the house in which I grew up in speech. Tell me about the day when you arrived is more natural than the day on which you arrived. Keep the short form unless you write something very formal.

• The woman whose son plays with mine is a doctor. Whose son shows possession, and the clause identifies which woman.
• We visited Lisbon, where my cousin lives, in spring. Commas show extra news about a known place.
• I remember the night when the power cut out. When links a time noun to what happened then.

Put prepositions in the right place

Prepositions in relative clauses sound formal or natural depending on position. Formal English puts the preposition before the pronoun. Everyday English leaves it at the end of the clause. Both are grammatical, but they suit different situations.

You would write the person to whom I spoke in a formal letter or an exam essay. You would say the person who I spoke to or the person I spoke to to a friend. The meaning is the same. The tone is different. Exams usually accept both, but very formal tasks expect the first form.

Note two limits. You cannot use that after a fronted preposition. You can say the film about which we talked, not the film about that we talked. And you cannot strand whose. You say the friend whose help I needed, not the friend whose I needed help from.

Fix five mistakes before they stick

Each of these errors appears in learner writing every week. Each one has a quick fix. Read your own sentences and check for the same pattern.

The most visible error is commas with that. My bag, that is red, is heavy breaks the rule. Say My bag, which is red, is heavy for extra news, or My bag that is red is heavy if you own several bags. Let the commas choose the pronoun.

The other errors change the structure. A double subject such as the man who he called adds one word too many. A missing subject such as the man called me drops one word too many. A wrong pronoun such as which for a person sounds careless even when the listener understands you.

1. Use of that with commas. Say Lisbon, which is beautiful, is worth a visit, not Lisbon, that is beautiful, is worth a visit.
2. A second subject inside the clause. Say the man who called, not the man who he called. The who already fills the subject slot.
3. A dropped subject pronoun. Say the man who called me is here, not the man called me is here. You can drop the object, never the subject.
4. Use of which for a person. Say the teacher who helped you, not the teacher which helped you. Keep which for things.
5. Commas around an identifying clause. Say Students who arrive late miss the warm-up, not Students, who arrive late, miss the warm-up. The second version wrongly says all students arrive late.

Conclusion

A relative clause saves you a second sentence. You point at a noun and add what your listener needs. Who marks people, which marks things, and that works for either when you identify.

Your commas carry the meaning. No commas means you identify which one. Commas mean you add news you could remove. Keep that out of commas, drop the pronoun only as the object, and place prepositions to match the tone you want.

Frequently asked questions

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