Defining and non-defining relative clauses modify a noun; one is needed for meaning and the other adds extra information with commas.
English learners meet relative clauses early, yet many still hesitate when they have to choose between defining relative clauses and non-defining relative clauses in real writing. Both structures attach extra information to a noun, but the way they affect meaning, punctuation, and pronoun choice is not the same. Once that contrast feels clear, sentences read more smoothly and punctuation choices stop feeling like a guess.
What Are Defining Relative Clauses And Non-Defining Relative Clauses?
A relative clause is a group of words with a subject and a verb that describes a noun. It usually begins with a relative word such as who, which, that, whose, where, or when. Many grammar references explain that defining relative clauses give information the reader needs about the noun, while non-defining clauses add extra information that is helpful but not necessary for identification.
A defining relative clause tells the reader exactly which person or thing you mean. If you remove it, the sentence either becomes unclear or its meaning changes.
Defining relative clause: The student who sits in the front row always asks good questions.
Without the clause who sits in the front row, we do not know which student you have in mind.
A non-defining relative clause gives extra detail about a noun that is already clear in the context. If you remove it, the main idea stays the same. In writing, this type of clause is set off with commas.
Non-defining relative clause: My sister, who lives in Canada, is visiting this month.
Here the listener already understands which sister you mean. The clause who lives in Canada adds background, but the main statement is simply that your sister is visiting.
| Aspect | Defining Relative Clause | Non-Defining Relative Clause |
|---|---|---|
| Purpose | Identifies which person or thing you mean | Adds extra detail about someone or something already clear |
| Effect On Meaning | Clause is needed for the sentence to make full sense | Clause can be removed without changing the basic message |
| Punctuation | No commas around the clause | Commas before and after the clause in writing |
| Typical Pronouns | who, which, that, whose, where, when | who, which, whose, where, when (usually not that) |
| Use With Names | Rare, because the name already identifies the person | Common, because we often add extra detail to a known person or place |
| Spoken Rhythm | Normally no pause around the clause | Speakers pause before and after the clause, echoing the commas |
| Example | The book that I bought yesterday was expensive. | My car, which I bought last year, is still in good condition. |
Defining And Non-Defining Relative Clauses In Real Sentences
Seeing both types side by side makes the contrast easier to feel. In each pair below, the defining version selects the person or thing, while the non-defining version adds a side comment about someone or something already identified.
Pair 1
Defining: Students who arrive late must sign a form.
Non-defining: My students, who arrive late sometimes, always apologise.
In the first sentence, only the late students must sign. In the second, the group my students is already known, and the clause comments on their habits.
Pair 2
Defining: The company that sells our textbooks has moved online.
Non-defining: Our company, which sells textbooks, has moved online.
The defining clause singles out one company among others. In the non-defining version, the company is already clear from context, and the clause simply states what it does.
When you write, ask yourself whether the clause helps the reader identify the noun or whether it simply comments on a person, place, or thing that is already identified. That simple test usually tells you whether you need a defining pattern or a non-defining one.
Relative Pronouns And Relative Adverbs
Both types of clause rely on a small set of relative words. Grammar references, including the Cambridge Dictionary grammar page on relative clauses and the British Council LearnEnglish explanation, give clear charts of these pronouns and adverbs. The list below follows the same pattern.
Common Relative Pronouns
- who — people, subject or object: The teacher who marked my test explained the mistakes.
- whom — formal object form for people, often after a preposition: The person to whom you spoke is my manager.
- which — animals and things: The laptop which I bought last week is already slow.
- that — people, animals, or things in defining clauses: The film that we watched was long.
- whose — possession for people and sometimes things: The author whose book you liked is speaking today.
Common Relative Adverbs
- where — places: This is the café where we met.
- when — times: That was the year when everything changed.
- why — reasons, mainly with reason: That is the reason why I left.
In defining relative clauses you can usually choose between who or that for people and between which or that for things. In non-defining clauses writers normally avoid that and stay with who or which. Those same choices appear again and again in examples on trusted grammar sites.
Subject Or Object Relative Pronoun
The role of the relative pronoun inside the clause also matters. When the relative word is the subject of the verb, you need to keep it.
The student who borrowed my notes has returned them. (Here who is the subject of borrowed.)
When the relative word is the object, many defining clauses drop it in everyday English.
The book (that) I ordered has arrived.
In non-defining clauses you normally keep the relative pronoun, because leaving it out would make the commas and pauses feel odd.
My book, which I ordered last week, has arrived. (You cannot leave out which here.)
Punctuation Rules And Comma Placement
Punctuation makes the difference between defining relative clauses and non-defining relative clauses visible on the page. In writing, defining clauses sit directly after the noun with no commas. Non-defining clauses are enclosed in commas because they feel like an aside to the reader.
Defining pattern: The teacher who lives near me cycles to work.
Non-defining pattern: My English teacher, who lives near me, cycles to work.
The commas around who lives near me show that this part can be removed while the core statement stays true. The same point appears in many teaching resources that compare defining and non-defining relative clauses.
Be careful with names and one-of-a-kind nouns. A name usually points to a specific person or place on its own, so any relative clause after a name will almost always be non-defining and take commas.
Maria, who grew up in Spain, speaks three languages. (Non-defining)
If you write The Maria who grew up in Spain, you suggest that there are several people called Maria and you want to separate one group from the others. That sort of sentence is rare and tends to appear only in special contexts.
Writers sometimes feel tempted to put commas around all relative clauses because they have seen commas near which in formal writing. Instead, decide first whether the information identifies the noun or simply comments on it. Then match your comma choice to that decision.
Common Mistakes And How To Fix Them
Even careful writers mix the two types or choose the wrong pronoun. This section lists frequent trouble spots and simple fixes so that your clauses match your meaning.
Using Commas With Defining Clauses
Many learners place commas around clauses that are actually defining. That punctuation changes the meaning of the sentence.
Incorrect: The people, who arrived late, missed the introduction.
Here the commas suggest that all the people arrived late, which is probably not what the writer meant.
Better: The people who arrived late missed the introduction.
Now the clause clearly limits the group. Only the late arrivals missed the introduction.
Using That In Non-Defining Clauses
Style guides usually advise against that in non-defining relative clauses. Readers expect who or which, and many teachers treat that in this position as wrong.
Unnatural: My laptop, that I bought last year, is still fast.
Natural: My laptop, which I bought last year, is still fast.
Choosing The Wrong Type For Your Message
Sometimes the choice between defining and non-defining relative clauses changes the whole message. Think carefully about whether you want to limit the noun or simply comment on it.
The teachers who live in the city use public transport. (Only teachers in the city.)
The teachers, who live in the city, use public transport. (All the teachers live in the city.)
Small shifts in commas and clause type change what the sentence claims about the group, so it helps to slow down and check that the structure matches the idea in your mind.
| Sentence Idea | Better Clause Type | Reason |
|---|---|---|
| Only the students who passed can join the trip | Defining | The clause limits which students may join |
| My parents, who live nearby, visit each weekend | Non-defining | Parents are already clear; the clause adds background |
| The emails that contain attachments are scanned | Defining | Only a subset of emails is described |
| Our office, which was renovated recently, feels brighter | Non-defining | The clause adds extra detail about one known office |
| The buses that stop here go to the city centre | Defining | The clause identifies which buses you are talking about |
| My brother, who works in finance, travels often | Non-defining | The job detail is extra information about a known person |
| The rooms that face the garden are quieter | Defining | The clause selects one group of rooms out of many |
Short Practice Exercises For Defining And Non-Defining Relative Clauses
Practice helps the contrast between defining relative clauses and non-defining relative clauses feel natural. You can write the answers in a notebook or say them aloud. The goal is to link structure and meaning in your own sentences.
Task 1: Decide The Type
Read each sentence and decide whether the relative clause is defining or non-defining.
- The library that opened last year has extended hours.
- Our library, which opened last year, has extended hours.
- The people who live upstairs are musicians.
- My neighbours, who live upstairs, are musicians.
Task 2: Join The Sentences
Join each pair of sentences with a suitable relative pronoun. Make one version with a defining clause and another with a non-defining clause.
- The boy is in my class. He won the prize.
- The building is on the corner. It used to be a bank.
- The river is polluted. It runs through the city.
With steady practice, the patterns in this article start to feel natural. You begin to hear when a clause identifies a noun and when it simply adds colour. Once that difference is clear, you can choose between defining relative clauses and non-defining relative clauses with confidence in essays, emails, and everyday messages.