A relative clause is a group of words that adds information about a noun, usually starting with who, whom, whose, which, or that. English has two main kinds: defining clauses, which identify exactly which person or thing you mean, and non-defining clauses, which add extra detail you could remove without losing the sentence’s core meaning. Getting the type right changes both your punctuation and, sometimes, your meaning.
This guide breaks down how each type works, which relative pronoun fits which situation, and the punctuation mistakes that trip up even confident writers.
Quick Answer
A relative clause modifies a noun and usually begins with who, whom, whose, which, or that. Defining relative clauses give essential information and use no commas: The book that I borrowed is overdue. Non-defining relative clauses give extra, removable information and need commas: My car, which is ten years old, still runs well. The clause type you choose determines both punctuation and, sometimes, meaning.
TL;DR
- Defining clauses identify the noun and never take commas.
- Non-defining clauses add extra detail and always take commas.
- A simple test: if you can delete the clause without losing essential meaning, it’s non-defining.
- Use who/whom for people, which for things, that for either in defining clauses only.
- You can often drop the pronoun in a defining clause when it’s the object: the book (that) I read.
- Whom is fading from everyday American speech but still expected in formal writing.
You Might Also Like That: ILY Meaning
The Three Types at a Glance
| Type | Commas? | Can You Remove It? | Example |
| Defining (restrictive) | No | No — changes meaning | The students who studied passed the exam. |
| Non-defining (non-restrictive) | Yes | Yes — meaning stays intact | My sister, who studied hard, passed the exam. |
| Zero (contact clause) | No | No, but the pronoun itself is optional | The book (that) I borrowed is overdue. |
What Is a Relative Clause?
A relative clause is a dependent clause that describes a noun in the main sentence. It cannot stand alone as a complete sentence. In The man who called earlier left a message, the relative clause who called earlier tells you which man you mean.
Relative clauses typically begin with a relative pronoun (who, whom, whose, which, that) or a relative adverb (where, when, why). The clause sits right after the noun it describes, which is called the antecedent.
Because English allows two very different relationships between a relative clause and its noun, the punctuation rule depends entirely on which relationship applies.
Defining vs. Non-Defining: The Core Distinction
A defining relative clause narrows down which person or thing you mean. Without it, the sentence loses essential meaning.
- The employees who arrived late missed the announcement. (Only the late employees missed it — the clause is essential.)
A non-defining relative clause adds extra information about something already identified. You could delete it and the sentence would still make full sense.
- My manager, who arrived late, missed the announcement. (You have one manager; the clause just adds detail.)
You Might Also Like That: There vs Their vs They’re
The remove-it test: Read the sentence without the relative clause. If the core meaning is unchanged, the clause is non-defining and needs commas. If removing it changes who or what you’re talking about, the clause is defining and takes no commas.
Compare these two sentences carefully, because they show how commas change meaning, not just style:
- My brother who lives in Denver is a teacher. (Implies you have more than one brother; this identifies which one.)
- My brother, who lives in Denver, is a teacher. (Implies you have only one brother; the clause is extra detail.)
Choosing the Right Relative Pronoun
The right pronoun depends on what you’re describing and whether the clause is defining or non-defining.
- Who — refers to people, as the subject of the clause: the woman who called
- Whom — refers to people, as the object of the clause: the woman whom I called
- Whose — shows possession, for people or things: the writer whose novel won an award
- Which — refers to things or animals, in either clause type: the car which broke down
- That — refers to people or things, but only in defining clauses: the car that broke down
A key American-English rule: that is common and accepted in defining clauses, but it should never follow a comma. If you’re using commas, switch to who, whom, or which instead of that.
Zero Relative Clauses: When You Can Drop the Pronoun
When the relative pronoun is the object of the clause and the clause is defining, you can often omit it entirely. This is called a zero or contact clause.
- The book (that) I borrowed is overdue.
- The man (whom) I met yesterday works downtown.
You cannot drop the pronoun when it’s the subject of the clause:
- Correct: The man who called earlier left a message.
- Incorrect: The man called earlier left a message. (This changes the sentence’s structure entirely.)
You also cannot omit the pronoun in a non-defining clause, since the comma-separated clause needs a clear connector to the main sentence.
You Might Also Like That: IYKYK Meaning
Relative Adverbs: Where, When, and Why
Relative adverbs work like relative pronouns but replace a preposition-plus-pronoun combination.
- Where replaces in/at which: the café where we met (instead of the café at which we met)
- When replaces in/on which: the year when we moved
- Why replaces for which: the reason why I called
These follow the same defining/non-defining comma rules as pronoun clauses: The house where I grew up was sold (defining, no commas) versus My childhood home, where I grew up, was sold (non-defining, commas required).
Whose for Possession
Whose shows ownership or a close relationship and works for both people and things, despite sounding like it should only apply to people.
- The employee whose badge was missing had to check in at the front desk.
- The company whose stock rose fastest last quarter is expanding.
Some writers avoid whose for objects and use of which instead (the company the stock of which rose fastest), but this sounds stiff in modern American English. Whose is the natural choice in nearly every context.
Whom in American English Today
Whom is grammatically correct whenever the relative pronoun functions as an object, but it has largely disappeared from everyday American speech. Most speakers say the person who I met rather than the person whom I met, even though whom is technically the object form.
You Might Also Like That: Effect vs Affect
In formal writing — reports, academic papers, professional correspondence — whom is still expected after prepositions and as a direct object: the client to whom I sent the proposal. In conversation and informal writing, who is widely accepted and rarely sounds wrong. Treat this as a register choice, not a hard error either way.
Common Mistakes with Relative Clauses
Mistake: Using that after a comma.
Incorrect: Her car, that was very old, broke down.
Correct: Her car, which was very old, broke down.
Non-defining clauses never use that — switch to which or who.
Mistake: Doubling the subject.
Incorrect: She’s the woman who she gave me directions.
Correct: She’s the woman who gave me directions.
Once who stands in for the subject, don’t repeat it with another pronoun.
Mistake: Missing commas on a non-defining clause.
Incorrect: My father who taught me to drive still gives me advice. (This wrongly implies you have more than one father.)
Correct: My father, who taught me to drive, still gives me advice.
Mistake: Dropping the pronoun when it’s the subject.
Incorrect: The employees arrived late missed the meeting.
Correct: The employees who arrived late missed the meeting.
You can only drop the pronoun when it functions as an object.
FAQs
Can “which” refer to a person?
No. Use who or whom for people and which for things, animals, or ideas. Using which for a person reads as a grammatical error in standard American English.
Is it wrong to start a sentence with a relative pronoun?
Yes, in most standard writing. Relative clauses attach to a noun in the same sentence, so they normally follow that noun rather than opening a new sentence on their own.
Do British and American English punctuate relative clauses differently?
The core defining/non-defining rule is the same in both. British writers sometimes use which more loosely in defining clauses where American style guides prefer that, but this is a style preference, not a hard grammar rule.
Can a relative clause come in the middle of a sentence?
Yes. Non-defining clauses especially often sit in the middle, right after the noun they describe: The report, which took months to finish, impressed the board.
What’s the difference between a relative clause and a relative pronoun?
A relative pronoun (who, which, that, and so on) is the word that introduces a relative clause. The relative clause is the entire group of words, including the pronoun, that describes the noun.
Can you use “that” for people?
Yes, in informal defining clauses: the man that called. Many style guides still prefer who for people in formal writing, but that is not incorrect.
Test Your Understanding
1. Which sentence uses a defining relative clause correctly?
A) The man, who called earlier, left a message.
B) The man who called earlier left a message.
C) The man, that called earlier, left a message.
D) The man whom called earlier left a message.
You Might Also Like That: TS Meaning in Text
2. Choose the correctly punctuated non-defining clause.
A) My laptop which is three years old still works fine.
B) My laptop, that is three years old, still works fine.
C) My laptop, which is three years old, still works fine.
D) My laptop which, is three years old still works fine.
3. Which sentence can correctly drop the relative pronoun?
A) The woman who called is my neighbor.
B) The book I borrowed is overdue.
C) The employees who arrived late missed the meeting.
D) My sister, who lives in Boston, is visiting.
4. Which pronoun correctly completes this sentence: “The scientist ___ research changed the field retired last year”?
A) who
B) whom
C) whose
D) which
5. Which sentence contains a relative-clause error?
A) The café where we met has closed.
B) She’s the teacher who she helped me the most.
C) The year when we moved was memorable.
D) The reason why I called was urgent.
Answer Key
- B — A defining clause identifying which man needs no commas, so B is correct; A and C wrongly add commas or use that after one, and D misuses whom as a subject.
- C — Non-defining clauses require commas on both sides and cannot use that; C is the only option that follows both rules.
- B — The pronoun is the object of borrowed, so it can be dropped; in A and C, the pronoun is the subject and cannot be omitted.
- C — Whose correctly shows possession between the scientist and the research.
- B — This doubles the subject with who and she; the correct form is She’s the teacher who helped me the most.
Conclusion
Relative clauses let you pack extra detail into a sentence without starting a new one, but the punctuation depends on whether that detail is essential. Defining clauses identify the noun and skip commas; non-defining clauses add removable detail and require them. Once you apply the remove-it test and match your pronoun to the clause type, most relative-clause mistakes disappear on their own.
