Defining vs. Non-Defining Relative Clauses (Commas and Meaning)
Grammar Rule in 30 Seconds
Defining clauses identify exactly which person or thing you mean; non-defining clauses just add extra, optional 'bonus' information using commas.
- Defining clauses have no commas and are essential for the sentence to make sense: 'The man who called left a message.'
- Non-defining clauses require commas and provide extra details: 'My father, who is 70, still runs marathons.'
- Never use the word 'that' in a non-defining clause; always use 'who' or 'which' instead.
Overview
These words give more details. They help you join ideas. There are two ways to use them.
The words you choose change the meaning of your sentence.
One way gives important facts. The other way gives extra facts. Use commas for extra facts.
Commas help the reader understand your idea. Good writing is clear.
How This Grammar Works
- Example:
The scientist who discovered the new particle won the Nobel Prize. - Analysis: Without
who discovered the new particle, the sentence becomesThe scientist won the Nobel Prize.This is vague. Which scientist? The clause is essential to identify the subject. It cannot be removed without losing the core meaning.
- Example:
Dr. Aris Thorne, who is a celebrated historian, gave the opening lecture. - Analysis: The noun
Dr. Aris Thorneis already specific. The clausewho is a celebrated historiangives us extra, interesting information, but we don't need it to know who gave the lecture. If you remove the clause, the sentenceDr. Aris Thorne gave the opening lectureremains complete and clear. The commas function like parentheses:Dr. Aris Thorne (a celebrated historian) gave the opening lecture.
Formation Pattern
which: For things. The report which you sent me is incomplete.
The engineer who designed the bridge retired. (who is the subject of designed).
The report [that] I wrote is on your desk. (I wrote the report, so that is the object and can be dropped).
who: For people. My colleague, who speaks four languages, is leading the negotiation.
whom: For people, as the object (formal). The CEO, whom I have never met, will be visiting our office.
which: For things. Our headquarters, which is located in Amsterdam, has over 500 employees.
When To Use It
- 1You need to answer the question "Which one?" Your clause specifies a particular item from a group of possibilities.
We need to fix the bugs that are crashing the system.(Specifies which bugs, not all bugs.)I want to meet the person who wrote this analysis.(Which person? The one who is the author.)
- 1The noun is general or common. Nouns like
the man,a company,the ideasare often too broad without a defining clause to restrict their meaning.
A city that has a good public transport system is more liveable.(Restricts the type of city being discussed.)
- 1The noun is already uniquely identified. This happens when the noun is:
- A proper name:
Eleanor Roosevelt, who was a champion of human rights, transformed the role of First Lady. - A unique noun/title:
My first manager, who taught me a great deal, retired last year. - A noun with a possessive:
Her latest novel, which I read in two days, is her best yet.
- 1The information is an aside or elaboration. The clause adds flavor, context, or an interesting fact rather than being a core identifier.
The sun, which is a star, is the center of our solar system.(There's only one sun in this context; its classification as a star is extra information.)This laptop, which I bought on sale, runs very fast.(The identity comes fromThis laptop; the fact it was on sale is a secondary detail.)
Common Mistakes
- 1Using
thatin a Non-Defining Clause: This is the most frequent and jarring mistake. As soon as you use commas to set off a clause,thatis grammatically incorrect.
- Incorrect:
Our office building, that has a great view, is downtown. - Correct:
Our office building, which has a great view, is downtown.
- 1The Meaning-Changing Comma Omission: Forgetting commas with a non-defining clause can fundamentally change your meaning by making the information sound essential.
- Sentence 1:
My brother who lives in Canada is an engineer.(Defining clause, no commas). The meaning is: I have more than one brother, and this clause identifies the specific one I'm talking about (the Canadian one). - Sentence 2:
My brother, who lives in Canada, is an engineer.(Non-defining clause, with commas). The meaning is: I have only one brother. His location in Canada is an additional, interesting fact about him.
- 1Incorrectly Omitting Pronouns in Non-Defining Clauses: Unlike defining clauses, the pronoun in a non-defining clause is a mandatory structural element.
- Incorrect:
Our company's founder, I greatly respect, still comes to the office. - Correct:
Our company's founder, whom I greatly respect, still comes to the office.
- 1Using Commas with Defining Clauses: This error is less common but still occurs. It incorrectly signals that essential identifying information is merely optional.
- Incorrect:
The email, that contains the password reset link, might be in your spam folder. - Correct:
The email that contains the password reset link might be in your spam folder.(The clause is essential to identify which email.)
Real Conversations
Native speakers use these structures constantly and intuitively across all levels of formality. The context and medium often influence the phrasing.
Professional & Academic Contexts:
- Work Slack/Teams message: Here’s the document that outlines the project goals. (Defining. that is common and efficient.)
- Formal Email: I am forwarding the proposal from Dr. Chen, who has approved the preliminary budget. (Non-defining. Dr. Chen is a specific person.)
- Academic Paper: The study focuses on subjects who have a specific genetic marker, which is associated with increased risk. (A defining clause to specify the subjects, followed by a non-defining clause to add information about the marker.)
Informal & Social Contexts:
- Text Message: that movie you told me about was awesome (Defining clause with the pronoun that omitted. Very natural.)
- Social Media Post: Finally visiting the Golden Gate Bridge, which is even more impressive in person! (Non-defining. The landmark is unique.)
- Casual Chat: My phone, which is only a year old, already has a cracked screen. (Non-defining. It's identified as My phone.)
A cultural insight
that is overwhelmingly preferred for defining clauses. The strict prescriptivist rule some older textbooks teach about using that for things and who for people is often ignored in favor of that for both. However, the rule against using that in non-defining clauses remains absolute in all standard varieties of English.Quick FAQ
Use the removal test. Read the sentence without the relative clause. Does the noun still refer to the same, specific thing? If yes, the clause is non-defining and needs commas. If the sentence becomes vague or the noun's identity is lost, the clause is defining and takes no commas.
In standard written English, no. This is one of the most reliable rules you can learn. Using which after a comma for things and who for people is the correct and expected pattern.
whom? It seems complicated.Use whom in formal contexts when the relative pronoun is the object. The artist whom the gallery featured... is more formal than The artist who the gallery featured.... In most modern usage, especially spoken, using who as the object is widely accepted. When in doubt, restructuring the sentence is also an option.
My sister, a doctor, lives in Boston and My sister, who is a doctor, lives in Boston?The first sentence uses an appositive phrase (a doctor) to rename the noun (sister). The second uses a non-defining relative clause (who is a doctor) to describe her. Their function is nearly identical—providing non-essential information—but the grammar is different. The appositive is a noun phrase, while the relative clause contains a verb.
In formal writing, especially with non-defining clauses, the preposition often comes before the pronoun (on which, to whom). For example: The theory, on which the book is based, is controversial. In most other contexts, it's far more common to leave the preposition at the end of the clause: The theory that the book is based on is controversial. This latter structure is standard for defining clauses.
Relative Pronoun Usage by Clause Type
| Pronoun | Used for... | Defining? | Non-Defining? | Can be omitted? |
|---|---|---|---|---|
|
Who
|
People
|
Yes
|
Yes
|
Yes (if object)
|
|
Which
|
Things/Animals
|
Yes
|
Yes
|
Yes (if object)
|
|
That
|
People/Things
|
Yes
|
NO
|
Yes (if object)
|
|
Whose
|
Possession
|
Yes
|
Yes
|
No
|
|
Whom
|
People (Object)
|
Yes (Formal)
|
Yes (Formal)
|
Yes
|
Meanings
Relative clauses provide more information about a noun. Defining clauses limit or 'define' the noun they follow, while non-defining clauses provide parenthetical information about a noun that is already clearly identified.
Identifying Senses
Used to specify exactly which member of a group we are talking about. Without this clause, the listener wouldn't know who or what is being discussed.
“The students who studied hard passed the exam.”
“I'm looking for the keys that I left on the table.”
Adding Extra Information
Used to give more detail about a noun that is already specific (like a proper name or a unique object). The sentence would still be clear without this information.
“London, which is the capital of the UK, is very expensive.”
“My brother, who lives in New York, is a chef.”
Sentential Relative Clauses
A specific type of non-defining clause using 'which' to comment on the entire preceding sentence or idea.
“He arrived late, which annoyed everyone.”
“She passed her driving test, which was a huge relief.”
Reference Table
| Type | Punctuation | Pronouns Allowed | Example |
|---|---|---|---|
|
Defining (Essential)
|
No Commas
|
who, which, that, whose
|
The man who lives next door is nice.
|
|
Non-Defining (Extra)
|
Commas Required
|
who, which, whose, whom
|
Mr. Jones, who lives next door, is nice.
|
|
Object Pronoun (Defining)
|
No Commas
|
(can be omitted)
|
The book I am reading is great.
|
|
Object Pronoun (Non-Def)
|
Commas Required
|
who, which, whom
|
This book, which I am reading, is great.
|
|
Sentential (Whole Idea)
|
Comma + Which
|
which
|
He was late, which was annoying.
|
|
Possessive
|
Depends on context
|
whose
|
The girl whose cat died is sad.
|
Formality Spectrum
The colleague to whom I spoke yesterday confirmed the meeting. (Workplace communication)
The colleague who I spoke to yesterday confirmed the meeting. (Workplace communication)
The guy I talked to yesterday said the meeting is on. (Workplace communication)
The dude I was chatting with yesterday says we're good for the meeting. (Workplace communication)
Defining vs. Non-Defining Visualized
Should I use a comma?
Is the information essential to identify the noun?
Examples by Level
The boy who is happy is my friend.
I have a dog which is big.
This is the cake that I like.
The man who lives there is old.
The hotel where we stayed was cheap.
Is that the girl who you met yesterday?
The book that you gave me is great.
I don't like people who are rude.
My sister, who is a nurse, works very hard.
Paris, which is in France, is beautiful.
The car that I bought last week has broken down.
He's the man whose car was stolen.
The report, which took me three days to write, is finally finished.
The candidates who have experience will be interviewed first.
She forgot her keys, which meant she had to wait outside.
The company for which he works is based in Tokyo.
The committee, none of whom agreed with the proposal, adjourned early.
The building, the roof of which was damaged in the storm, is being repaired.
It was a decision the consequences of which were not yet clear.
He was a man for whom honor meant everything.
The research, the findings of which have been widely disputed, remains influential.
She made a series of errors, the most egregious of which was the loss of the client's data.
The city, whose history is as rich as it is bloody, attracts millions of tourists.
He spoke with a slight accent, which I couldn't quite place.
Easily Confused
Learners often use them interchangeably, but 'that' cannot follow a comma.
Learners struggle with subject vs. object pronouns.
Common Mistakes
The man which lives here.
The man who lives here.
The book what I read.
The book that I read.
My mother, that is a doctor, is 50.
My mother, who is a doctor, is 50.
The company, who is based in London, is growing.
The company, which is based in London, is growing.
Sentence Patterns
The ___ who/that ___ is ___.
[Name], who ___, is ___.
Real World Usage
I am a marketing professional who specializes in SEO.
The Prime Minister, who visited Paris yesterday, signed a new treaty.
Did you see the photo I posted?
The Tenant, who shall be referred to as 'The Occupant', agrees to...
The museum, which houses the world's largest collection of coins, is open daily.
Select the items that you want to add to your cart.
The Delete Test
The 'That' Rule
Proper Nouns
Speaking the Commas
Smart Tips
Automatically reach for the commas. Names are already specific, so any relative clause following them is almost certainly non-defining.
Omit the relative pronoun in defining clauses if it's the object. It sounds much less 'textbook'.
Use 'which' for defining clauses instead of 'that' to sound more academic and sophisticated.
Use a sentential 'which' at the end of your sentence. It's a great way to show your opinion.
Pronunciation
The Comma Pause
In non-defining clauses, there is a slight drop in pitch and a brief pause before and after the clause.
Parenthetical Dip
My car, ↘ which is blue, ↗ is outside.
The lower pitch indicates the information is secondary/extra.
Memorize It
Mnemonic
D-N-C: Defining = No Commas. N-D-C: Non-Defining = Do Commas.
Visual Association
Imagine the commas in a non-defining clause are like a pair of scissors. You can use them to 'cut out' the extra information, and the sentence will still stand perfectly fine on its own.
Rhyme
If the info is just a 'plus', use a comma without a fuss. If it tells us 'which is who', then no commas are for you.
Story
Think of a detective. A detective needs 'Defining' information to catch a specific thief ('The thief who has a scar'). A gossip columnist gives 'Non-defining' information ('The thief, who has a scar, was seen at the mall'). The detective needs the info to identify; the columnist just wants to add details.
Word Web
Challenge
Look at three objects in your room. Write one sentence for each using a defining clause to identify it, and one sentence using a non-defining clause to add a fun fact about it.
Cultural Notes
In US English, there is a very strong preference for using 'that' for defining clauses and 'which' exclusively for non-defining clauses. Using 'which' in a defining clause often sounds overly formal or British to Americans.
In formal academic contexts, 'whom' is still strictly required after prepositions, and non-defining clauses are used extensively to provide citations and background context.
Relative pronouns in English evolved from interrogative pronouns (who/which) and demonstrative pronouns (that).
Conversation Starters
Tell me about a friend who has an interesting job.
What is a city you've visited that you'll never forget?
Journal Prompts
Common Mistakes
Test Yourself
Which sentence is punctuated correctly?
The laptop ___ I bought yesterday is already broken.
Find and fix the mistake:
The painting, that was stolen last week, has been found.
My father is 70. He still plays tennis every day.
You can omit the relative pronoun in a non-defining clause if it is the object.
The car *that has the flat tire* is mine.
Match each item on the left with its pair on the right:
A: Which coat is yours? B: It's the one ___.
Score: /8
Practice Exercises
8 exercisesWhich sentence is punctuated correctly?
The laptop ___ I bought yesterday is already broken.
Find and fix the mistake:
The painting, that was stolen last week, has been found.
My father is 70. He still plays tennis every day.
You can omit the relative pronoun in a non-defining clause if it is the object.
The car *that has the flat tire* is mine.
1. The students who were late failed. | 2. The students, who were late, failed.
A: Which coat is yours? B: It's the one ___.
Score: /8
Practice Bank
11 exercisesThe restaurant ___ we had dinner last night was fantastic.
My neighbor, who is a doctor that works at the hospital, is very kind.
Choose the correct sentence:
Translate into English: 'El perro, que tiene manchas, es muy amigable.'
Arrange these words into a sentence:
Match the relative clause type with its punctuation:
My new smartphone, ___ has a fantastic camera, was quite expensive.
Students, who don't study, often fail exams.
Translate into English: 'Busco el libro que me recomendaste.'
Choose the correct sentence:
The decision ___ they made affected everyone.
Score: /11
FAQ (8)
Yes, you can. However, in American English, 'that' is much more common. In British English, 'which' is used more frequently in defining clauses, but 'that' is still very common.
This is a formal rule of English grammar. 'That' is considered a restrictive pronoun, meaning its job is to limit or define. Non-defining clauses don't limit; they just add, so 'who' or 'which' are required.
You can only leave them out in *defining* clauses when the pronoun is the *object* of the verb. For example: 'The book [that] I bought.' You can never leave them out in non-defining clauses.
Yes, but mostly in very formal writing or after prepositions (e.g., 'The person to whom I was speaking'). In casual speech, most people just use 'who' or leave it out.
Only if the clause is in the middle of the sentence. If the clause ends the sentence, you only need the opening comma (e.g., 'I live in London, which is huge.').
It's a clause starting with `, which` that describes the whole previous sentence. Example: 'He lied to me, which really hurt my feelings.'
Yes! 'Whose' is the possessive form for both people and things. Example: 'The car whose alarm is going off is mine.'
Yes. You can have defining clauses ('The day when we met') and non-defining clauses ('In 2020, when the pandemic started, ...').
Scaffolded Practice
1
2
3
4
Mastery Progress
Needs Practice
Improving
Strong
Mastered
In Other Languages
Oraciones de relativo (especificativas vs. explicativas)
English has a stricter 'no that after commas' rule.
Relativsätze
German requires commas for defining clauses; English forbids them.
連体修飾節 (Rentai shuushikusetsu)
Japanese has no relative pronouns and no comma distinction.
Propositions relatives
French doesn't have a 'that' equivalent that is restricted to defining clauses.
الصلة (Al-Sila)
Arabic relative structure depends on the definiteness of the noun.
的 (de) structure
Chinese relative clauses come before the noun.
Learning Path
Prerequisites
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