---
title: "Relative Clause: The Two Commas That Change the Meaning"
url: https://www.learningloftinstitute.com/glossary/relative-clause
source: Learning Loft Institute
language: en
updated: 2026-08-21
section: "Glossary › Relative Clause: The Two Commas That Change the Meaning"
---
# Relative Clause: The Two Commas That Change the Meaning
> **Answer.** A relative clause gives more information about a noun and usually begins with who, which, that, whose, where or when. Commas decide its job: without them it identifies which one you mean; with them it is an aside you could delete without losing track of who is being talked about.
## Key facts
| | |
| --- | --- |
| Definition | A relative clause is a subordinate clause that describes a noun, usually introduced by a relative pronoun such as who, which, that or whose. |
| Where students meet it | Grade 5 English; the national curriculum for England introduces relative clauses and relative pronouns in Year 5, including clauses where the relative pronoun is left out. |
| Also known as | Adjectival clause |
## Defining or non-defining: the commas decide
A defining relative clause is essential. Remove it and the sentence no longer tells you which person or thing is meant. It takes no commas, because nothing is being set aside.
A non-defining relative clause is extra. Remove it and the sentence still identifies its subject perfectly well. It takes commas at both ends, and the second one is the comma people forget, which leaves a sentence half-punctuated and marked wrong.
The test is deletion. Cross the clause out and read what is left. If you can no longer tell which one is meant, the clause was defining and the commas must go. If the sentence is still clear, the commas belong.
## Choosing between who, which and that
The introducing word is chosen by what the noun is, and by whether the clause is defining.
- who, whom, whose — people. The teacher who marked it; the boy whose bag was lost.
- which — things and animals. The book which won the prize.
- that — people or things, but only in a defining clause. The book that won the prize is fine; the book, that won the prize, is not.
- where, when — places and times. The town where she was born; the year when the school opened. These are relative adverbs rather than pronouns, but they introduce relative clauses in the same way.
## The relative pronoun you are allowed to leave out
The rule worth memorising from that list is the one about that: it cannot introduce a non-defining clause. If commas are needed, the word has to be which or who.
The book I read last week is a relative clause with the pronoun missing; the book that I read last week is the full form. English allows the omission only when the relative pronoun is the object of its own clause. That is why the boy sits next to me is wrong while the boy who sits next to me is right — there, who is the subject and cannot go.
The national curriculum for England names the omitted relative pronoun explicitly in Year 5, so primary pupils are expected to recognise these clauses even with no signal word present. It is also why some pupils fail to find a relative clause in a text: they are hunting for who or which and there is not one.
## Questions
### When do you use commas with a relative clause?
When the clause is extra information rather than information that identifies the noun. Try deleting it. If the sentence still makes clear who or what is meant, use commas at both ends. If deleting it leaves you unable to tell which one, use no commas at all.
### What is the difference between a relative clause and a subordinate clause?
A relative clause is one type of subordinate clause. Both depend on a main clause. What makes a clause relative is that it describes a noun and usually opens with who, which, that or whose. An adverbial clause such as because it rained is subordinate but not relative.
### Can you use that instead of which?
In a defining clause, yes: the file that was missing and the file which was missing are both acceptable in British English. In a non-defining clause, no. Once commas are involved, only which or who will do, so the file, that was missing, turned up is wrong.
### Does whom still matter?
In formal writing and exam answers, yes, although it is rare in speech. Use whom when the pronoun is the object of its clause — the candidate whom we interviewed — and who when it is the subject — the candidate who applied. If you are unsure, rephrasing to avoid it is safer than guessing.
## Sources
1. National curriculum in England: English programmes of study — Department for Education. https://www.gov.uk/government/publications/national-curriculum-in-england-english-programmes-of-study/national-curriculum-in-england-english-programmes-of-study (accessed 2026-08-21)
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