A relative clause is a dependent clause that modifies a noun or pronoun by adding identifying or descriptive information. It usually begins with a relative pronoun such as who, whom, whose, which, or that, or a relative adverb such as where, when, or why. The clause normally follows the noun it describes.
Key facts
A relative clause contains a subject and a verb but cannot stand alone as a complete sentence.
The noun modified by a relative clause is called its antecedent.
Defining relative clauses identify which person or thing a sentence means and use no commas.
Non-defining relative clauses add extra information and require commas.
That is common in defining clauses but does not introduce non-defining clauses.
A relative pronoun can be omitted only when it functions as the object in a defining clause.
What Is a Relative Clause?
A relative clause is a subordinate clause that acts like an adjective because it describes or identifies a noun. In The mechanic who repaired my car is my uncle, the clause who repaired my car modifies mechanic. The clause has its own verb, repaired, but it depends on the main clause for complete meaning.
Relative clauses make writing more compact by combining related thoughts. The repetitive version, The mechanic repaired my car. The mechanic is my uncle, becomes The mechanic who repaired my car is my uncle. The relative clause connects the two ideas without repeating the mechanic.
Relative clauses versus adjective phrases
An adjective phrase does not contain a finite verb, while a relative clause does.
| Structure | Example | Modifier |
|---|---|---|
| Single adjective | The damaged bicycle was expensive. | damaged |
| Adjective phrase | The bicycle badly damaged in transit was expensive. | badly damaged in transit |
| Relative clause | The bicycle that was damaged in transit was expensive. | that was damaged in transit |
| Noun clause | I know what the bicycle costs. | what the bicycle costs is a noun clause |
The term relative describes the connection between the clause and its antecedent. In the book that I borrowed, that refers back to book.
How Does a Relative Clause Work?
A relative clause follows its antecedent and fills a grammatical role inside the clause. The relative word may be the subject, the object, a possessive determiner, or an adverbial link showing place, time, or reason.
Consider The researcher who discovered the error reported it immediately. Who is the subject of discovered. In The error that the researcher discovered was serious, that is the object of discovered, while the researcher is the subject.
A reliable construction process has four steps:
- Identify the antecedent. Decide which noun needs more information.
- Choose the relative word. Match the word to meaning and grammatical role.
- Decide whether the information is essential. Essential information takes no commas; extra information takes commas.
- Place the clause directly after the antecedent. Immediate placement prevents attachment errors.
Sentence-combining example
Start with two sentences:
- The museum opened in 1890.
- The museum attracts 200,000 visitors annually.
Combine them as:
- The museum, which opened in 1890, attracts 200,000 visitors annually.
The clause which opened in 1890 supplies additional information. The commas show that the museum is already identified.
What Are the Main Types of Relative Clauses?
The two main types are defining, also called restrictive, and non-defining, also called non-restrictive. The difference is semantic: defining clauses narrow the noun’s reference, while non-defining clauses add commentary about an already identified noun.
| Feature | Defining clause | Non-defining clause |
|---|---|---|
| Information | Identifies the noun | Adds optional information |
| Commas | No commas | Commas required |
| Common relative words | who, which, that, whose | who, whom, which, whose |
| Use of that | Permitted | Not permitted |
| Pronoun omission | Possible for an object | Not possible |
| Meaning after removal | May change | Usually remains identifiable |
Defining relative clauses
A defining clause is necessary to identify the intended person or thing.
- The employees who completed the training received certificates.
- The laptop that I ordered arrived today.
- The road which leads to the village is closed.
In the first example, the clause may mean that only the employees who completed the training received certificates. Removing it leaves The employees received certificates, which has a broader meaning.
Non-defining relative clauses
A non-defining clause gives extra information about a noun that is already clear.
- Dr. Patel, who teaches linguistics, published a new textbook.
- The Amazon River, which crosses several countries, carries enormous volumes of water.
- My office, where I write every morning, overlooks the park.
A non-defining clause must be separated with commas. The commas are not optional decoration because they signal that the clause does not restrict the noun’s identity.
Compare:
- My brother who lives in Toronto is a pilot.
This may imply that I have more than one brother, and the Toronto-based brother is the pilot. - My brother, who lives in Toronto, is a pilot.
This presents one already identified brother and adds his location.
Which Relative Word Should You Use?
The correct relative word depends on the antecedent, its grammatical role, and the formality of the sentence. Who and whom refer to people, which usually refers to things or animals, and that works for people or things in defining clauses.
| Relative word | Typical reference | Clause role | Example |
|---|---|---|---|
| who | People | Subject or object | The nurse who called is here. |
| whom | People | Object, formal | The client whom we contacted replied. |
| whose | People, animals, things | Possession | The company whose data was lost apologized. |
| which | Things, animals | Subject or object | The device which failed was replaced. |
| that | People, animals, things | Subject or object | The report that changed policy was brief. |
| where | Places | Place adverb | The clinic where I work closes at six. |
| when | Times or periods | Time adverb | The year when prices rose was difficult. |
| why | Reasons | Reason adverb | The reason why she left is unknown. |
Who and whom
Use who when the relative pronoun performs the action:
- The engineer who designed the bridge won an award.
Use whom when the pronoun receives the action or follows a preposition in formal English:
- The engineer whom the committee interviewed won an award.
- The engineer with whom I worked moved abroad.
A practical substitution test helps: if he or she fits, use who; if him or her fits, use whom.
- Who/whom designed the bridge? She designed it, so use who.
- The committee interviewed who/whom? It interviewed him, so formal usage selects whom.
In everyday speech, many speakers use who instead of whom, especially when the pronoun does not follow a fronted preposition.
Which and that
Use which for things and animals, especially in non-defining clauses:
- The printer, which was installed last week, has stopped working.
Use that in defining clauses when the reference may be a person, animal, or thing:
- The printer that we installed last week has stopped working.
- The consultant that joined the meeting arrived late.
Formal style often prefers who for people, but the claim that that is always incorrect for humans is too strong. Major English varieties use that for people in defining clauses, particularly in speech and concise writing. The comma rule is absolute: do not use that after a comma to introduce a non-defining clause.
When Can You Omit a Relative Pronoun?
You can omit who, whom, which, or that when it is the object of a verb or preposition in a defining clause. You cannot omit it when it is the subject, and omission is not allowed in a non-defining clause.
| Full form | Omitted form | Reason |
|---|---|---|
| The film that I watched was long. | The film I watched was long. | that is the object |
| The person whom we hired starts Monday. | The person we hired starts Monday. | whom is the object |
| The tool which she used was damaged. | The tool she used was damaged. | which is the object |
| The scientist who discovered it retired. | Not possible | who is the subject |
| The machine that failed was repaired. | Not possible | that is the subject |
| The car, which I bought in May, is reliable. | Not possible | non-defining clause |
To test omission, look for another noun or pronoun before the verb. In the book that I read, I is the subject, so that is the object and can disappear. In the book that changed my view, that is the subject of changed, so it must remain.
How Do Relative Adverbs Work?
Relative adverbs connect an antecedent to information about place, time, or reason. Where means “in or at which,” when means “at which time,” and why means “for which reason.”
- This is the town where my grandparents met.
- I remember the day when we moved house.
- No one explained the reason why the system failed.
The relative adverb can often be replaced with a preposition plus which:
- The town in which my grandparents met
- The day on which we moved house
- The reason for which the system failed
The alternatives differ in register. Where and when are shorter and natural in general writing, while in which and on which are more formal. With reason, many writers omit why entirely: No one explained the reason the system failed.
How Do Commas Change the Meaning?
Commas determine whether a relative clause identifies the noun or merely comments on it. A no-comma clause restricts reference; a comma-separated clause assumes the noun is already identified.
- The buildings that survived the earthquake need inspection.
Only the surviving buildings need inspection. - The buildings, which survived the earthquake, need inspection.
The sentence presents all the buildings as survivors.
Use non-defining punctuation with proper names, unique institutions, and clearly identified nouns:
- Maria, who lives nearby, joined the project.
- Mount Everest, which is in the Himalayas, attracts climbers.
- The Pacific Ocean, which covers more than 155 million square kilometres, influences global climate.
Do not use commas merely because a clause is long. Length does not determine punctuation. Meaning does.
What Are Reduced Relative Clauses?
A reduced relative clause is a shortened relative clause, often formed with a present participle, past participle, or infinitive. Reduction can make technical and academic prose more compact, but the omitted material must remain recoverable.
| Full relative clause | Reduced form | Meaning |
|---|---|---|
| The students who are waiting outside may enter. | The students waiting outside may enter. | Active, simultaneous action |
| The samples that were collected yesterday are frozen. | The samples collected yesterday are frozen. | Passive meaning |
| The first person who arrives chooses a seat. | The first person to arrive chooses a seat. | Earliest action |
| The data that was stored on the server disappeared. | The data stored on the server disappeared. | Passive past participle |
Do not reduce a clause when the result creates ambiguity or changes the subject. The report discussing the manager means the report discusses the manager, while the manager discussing the report means the manager performs the discussing.
How Should Relative Clauses Be Used in Formal Writing?
Formal writing benefits from precise defining clauses and restrained non-defining clauses. Use who for people when the tone is academic or professional, retain prepositions before whom when clarity or formality matters, and avoid stacking several long clauses inside one sentence.
| Context | Preferred example | Register |
|---|---|---|
| Conversation | The person that I spoke to was helpful. | Natural, informal |
| General writing | The person who I spoke to was helpful. | Standard |
| Formal writing | The person to whom I spoke was helpful. | Formal |
| Technical writing | The device that records pressure needs calibration. | Precise, defining |
| Academic prose | The study, which examined 400 participants, found no effect. | Formal, non-defining |
A fronted preposition is grammatically formal but can sound stiff in ordinary speech. The department in which she works is correct; the department she works in is also correct and usually more conversational.
What Common Relative-Clause Errors Should You Fix?
Relative-clause errors usually involve duplicated objects, incorrect punctuation, unclear attachment, or disagreement between the relative clause verb and its antecedent.
1. Avoid the double pronoun
Incorrect: The phone that I bought it yesterday is broken.
Correct: The phone that I bought yesterday is broken.
The word that already represents the phone as the object of bought. Adding it duplicates that object.
2. Place the clause beside its antecedent
Ambiguous: We gave the treats to the dogs that were covered in chocolate.
Clear: We gave the treats that were covered in chocolate to the dogs.
The first version grammatically places that were covered in chocolate beside dogs, so it suggests the dogs had chocolate on them.
3. Do not use that after a comma
Incorrect: London, that is the capital of the United Kingdom, is historic.
Correct: London, which is the capital of the United Kingdom, is historic.
Non-defining clauses use who, whom, which, or whose, not that.
4. Match the verb with the antecedent
Correct: She is one of the researchers who are presenting today.
Here, who refers to the plural noun researchers, so the verb is are. The nearby singular noun one does not control agreement inside the relative clause.
Compare:
- She is the only researcher who is presenting today.
- She is one of the researchers who are presenting today.
5. Prevent vague antecedents
Unclear: The manager spoke to the assistant about the schedule, which caused confusion.
Does which refer to the schedule, the conversation, or the entire preceding situation? Rewrite the sentence:
- The manager’s conversation with the assistant caused confusion.
- The schedule caused confusion after the manager discussed it with the assistant.
A relative clause should identify a specific antecedent, not force readers to guess what a pronoun represents.
Which Alternatives Can Replace a Relative Clause?
Relative clauses can be replaced by separate sentences, adjective phrases, participial phrases, or appositives. The best alternative depends on sentence length, information priority, and the risk of ambiguity.
| Relative-clause version | Alternative | Best use |
|---|---|---|
| The bridge that crosses the river is closed. | The bridge crossing the river is closed. | Compact description |
| The bridge, which crosses the river, is closed. | The bridge crosses the river. It is closed. | Maximum clarity |
| Dr. Lee, who leads the team, approved it. | Dr. Lee, the team leader, approved it. | Appositive style |
| The files that were stored locally were deleted. | Locally stored files were deleted. | Technical compression |
| The reason why sales fell is unclear. | The reason for the decline in sales is unclear. | Formal noun phrase |
Relative clauses are not always the best choice. Separate sentences work better when a clause contains several embedded ideas, when the antecedent is distant, or when the reader must process legal, medical, or safety instructions quickly.
A Practical Editing Checklist
Use this checklist when writing or reviewing a relative clause:
- Underline the antecedent and confirm that the relative clause modifies it.
- Check whether the clause identifies the noun or adds optional information.
- Remove commas from defining clauses and add them around non-defining clauses.
- Choose who, whom, which, that, whose, where, when, or why according to grammatical role.
- Check whether the relative word is a subject or object.
- Omit an object pronoun only in a defining clause.
- Remove duplicated words such as it, him, her, or them.
- Check subject-verb agreement inside the relative clause.
- Read for ambiguous attachment.
- Split the sentence if the clause becomes longer than the main idea can support.
FAQ
Can a relative clause begin a sentence?
A relative clause normally follows the noun it modifies, so it does not usually begin an independent sentence. However, a clause can appear at the beginning when its antecedent is understood from a preceding noun phrase, as in Those who arrive early can enter first. Here, who arrive early modifies those.
Is a relative clause the same as a subordinate clause?
A relative clause is one type of subordinate clause. Both depend on a main clause, but a relative clause specifically modifies a noun or pronoun. An adverbial clause modifies a verb or whole clause, as in because the road was closed, while a noun clause fills a noun role, as in what she decided.
Can relative clauses modify pronouns?
Yes. Relative clauses can modify indefinite or demonstrative pronouns such as someone, anyone, those, and everything. Examples include Anyone who submits late must explain why and Those who disagree may appeal. In these sentences, the relative clause identifies the members of the pronoun’s group.
Should I use which or that for animals?
Use which for an animal in a non-defining clause and that or which in a defining clause, depending on style. For example, My dog, which is six years old, needs exercise adds information, while The dog that chased the cyclist was rescued identifies one particular dog.
Why is a relative clause called dependent?
A relative clause is dependent because it cannot normally express a complete independent statement. Who lives next door leaves the reader waiting for an antecedent and a main clause. The complete sentence The woman who lives next door is a doctor supplies both the modified noun and the main assertion.
Can I use two relative clauses in one sentence?
Yes, but the clauses must have clear antecedents and manageable structure. The analyst who prepared the report that the board approved received a promotion is grammatical, although two nested clauses increase processing difficulty. Splitting it into two sentences may improve clarity in business, legal, and technical writing.
The Bottom Line
Relative clauses modify nouns by identifying them or adding information about them. Defining clauses use no commas and can use that; non-defining clauses require commas and use who, whom, which, or whose instead. Choose the relative word by grammatical role, place the clause beside its antecedent, and remove object pronouns only when the structure permits omission. Understanding these rules makes the definition, usage, and examples of relative clauses practical rather than memorized.
