A relative clause is a dependent clause that identifies or adds information about a person, thing, place, or time. It usually follows the noun it modifies and often begins with who, which, that, or another relative word. Relative clauses are also commonly called adjective clauses because they modify nouns or pronouns.
Consider:
The invoice that contained the duplicate charge has been corrected.
The highlighted clause identifies which invoice needed correction. Within the clause, that refers to the invoice and functions as the subject of contained.
But a relative clause does not always have an introductory relative pronoun:
The invoice the accountant questioned has been corrected.
Here, the accountant questioned identifies the invoice. The object relative pronoun that or which could be included before the accountant, but it is not required.
Both sentences contain relative clauses, although their structures differ. Understanding those differences helps explain when relative words can be omitted, how prepositions work within relative clauses, and why some constructions require particular forms.
Defining and Non-Defining Relative Clauses
Relative clauses can identify a particular person or thing or add information about someone or something already identified.
Defining Relative Clauses
A defining relative clause, also called a restrictive relative clause, limits the reference of a noun or pronoun.
The visiting researchers who arrived on Tuesday attended the briefing.
The clause identifies the researchers who arrived on Tuesday. The sentence does not tell us whether researchers arriving on other days attended.
Defining clauses are not separated from the noun by commas.
Non-Defining Relative Clauses
A non-defining relative clause, also called a non-restrictive relative clause, adds information about someone or something already identifiable.
The visiting researchers, who arrived on Tuesday, attended the briefing.
Here, the visiting researchers refers to an identifiable group. The relative clause adds that they arrived on Tuesday.
Non-defining clauses are separated by commas. When one appears in the middle of a sentence, a comma normally appears on each side.
That is used in defining relative clauses, not ordinary non-defining ones.
Incorrect: The original contract, that was signed in June, has been misplaced.
Correct: The original contract, which was signed in June, has been misplaced.
In defining clauses referring to things, both that and which are grammatical:
The contract that the supplier signed is missing.
The contract which the supplier signed is missing.
Some American editorial styles prefer that for defining clauses. British English commonly uses either form.
The difference between defining and non-defining clauses concerns how the information identifies its reference, not simply how important that information is.
How Relative Pronouns Work Inside a Clause
Relative pronouns can serve different grammatical roles within their clauses. Those roles influence whether a pronoun can be omitted and where a preposition may appear.
| Role | Example | Relationship |
|---|---|---|
| Subject | The engineer who approved the design | The engineer approved the design |
| Object | The design that the engineer approved | The engineer approved the design |
| Prepositional complement | The consultant whom we spoke to | We spoke to the consultant |
| Possessive relationship | The architect whose proposal succeeded | The proposal belongs to or is associated with the architect |
Subject and Object Relative Pronouns
Consider:
The biologist who identified the rare species published her observations.
Who is the subject of identified, because the biologist performed the action.
Now compare:
The manuscript which the editor returned contained several missing pages.
The editor returned the manuscript. Here, which represents the object of returned.
When referring to people, who can also function as an object in everyday English:
The candidate who the panel interviewed yesterday has accepted the offer.
In more formal writing, whom may be used instead:
The candidate whom the panel interviewed yesterday has accepted the offer.
Both are grammatical. The choice reflects differences in register rather than a difference in the underlying relationship.
Whose and Possessive Relationships
Whose expresses possession or another close association.
The architect whose design won the competition will oversee the project.
The design is associated with the architect.
Whose can also refer to organisations and things:
The company whose records were lost in the fire has begun reconstructing its accounts.
Unlike an optional object relative pronoun, whose cannot simply be removed while leaving the remaining clause unchanged.
When Can a Relative Pronoun Be Omitted?
An object relative pronoun can often be omitted from a defining clause.
The letter that the solicitor requested arrived this morning.
The solicitor requested the letter, so that represents the object of requested.
The sentence remains grammatical without it:
The letter the solicitor requested arrived this morning.
A subject relative pronoun normally cannot be omitted from a finite relative clause.
The witness who noticed the broken seal informed the supervisor.
Removing only who would leave an ungrammatical construction.
Incorrect: The witness noticed the broken seal informed the supervisor.
Correct: The witness who noticed the broken seal informed the supervisor.
Don’t Repeat the Object
When the relative pronoun already represents the object, adding another object pronoun creates unnecessary duplication.
Incorrect: The photographs that the curator selected them were displayed upstairs.
Correct: The photographs that the curator selected were displayed upstairs.
You can omit that here, but you cannot add them to repeat its object.
Relative Clauses With Prepositions
A preposition can remain at the end of a relative clause or appear before a relative pronoun.
Compare:
| Construction | Example |
|---|---|
| Everyday, without a relative pronoun | The adviser I spoke to recommended a different policy. |
| Everyday, with a relative pronoun | The adviser who I spoke to recommended a different policy. |
| More formal | The adviser to whom I spoke recommended a different policy. |
All three identify the adviser.
In the first two, to remains at the end of the relative clause. In the formal version, it appears before whom.
When a preposition comes directly before a relative pronoun referring to a person, formal standard English normally uses whom, not who.
Correct: The adviser to whom I spoke.
Incorrect in standard formal English: The adviser to who I spoke.
Why That Cannot Follow a Fronted Preposition
That cannot normally appear immediately after a fronted preposition.
Incorrect: The policy under that they were insured has expired.
Correct: The policy under which they were insured has expired.
Correct: The policy that they were insured under has expired.
The object relative pronoun can also be omitted from the last version:
The policy they were insured under has expired.
Some of Whom and Two of Which
Non-defining relative clauses can identify part of a larger group.
Twelve applicants attended the interview, three of whom had previous teaching experience.
The clause identifies three people within the group of twelve.
The same pattern works with things:
The library received eight donated manuscripts, two of which required restoration.
This allows the smaller group to be identified without repeating the noun.
Relative Clauses With Where, When, and Why
Relative clauses can also express relationships involving places, times, and reasons.
Where for Places
The studio where they recorded the soundtrack has become a museum.
The recording took place in the studio.
A more formal alternative is:
The studio in which they recorded the soundtrack has become a museum.
However, where cannot replace which or that in every relative clause referring to a place.
Compare:
The museum where we held the workshop has reopened.
The museum that reopened in April is near the station.
In the first sentence, where identifies the location of the workshop.
In the second, the museum itself reopened, so that functions as the subject of reopened.
When for Times
The evening when the emergency lights came on is still remembered by the residents.
The clause identifies a particular evening through an event that happened then.
In more formal writing, we could use on which instead of when:
The evening on which the emergency lights came on is still remembered by the residents.
Why for Reasons
The reason why the launch was postponed was not explained.
Here, the clause identifies the reason being discussed.
Why is often optional after reason:
The reason the launch was postponed was not explained.
Both forms are natural.
Reduced Relative Clauses
Certain relative clauses can be shortened to participial constructions.
Consider:
The documents that were submitted yesterday require approval.
This can be shortened to:
The documents submitted yesterday require approval.
The shorter version uses a past-participial modifier.
A similar pattern occurs with present participles:
The employees who are working overnight will receive transport assistance.
The employees working overnight will receive transport assistance.
Only certain relative clauses allow this kind of shortening. The resulting construction must remain grammatical and preserve the intended meaning.
Reduction vs. Relative-Pronoun Omission
These are different grammatical changes.
Object relative pronoun omitted:
The report that the analyst prepared was published.
The report the analyst prepared was published.
Only that has been omitted. The subject the analyst and the finite verb prepared remain.
Relative clause shortened to a participial construction:
The report that was prepared by the analyst was published.
The report prepared by the analyst was published.
In the second sentence, that was prepared has been shortened to the participial modifier prepared by the analyst.
The distinction matters because omitting a relative pronoun does not necessarily change the verb structure, while participial shortening does.
When Which Refers to an Entire Statement
Which can sometimes refer to an entire preceding statement or event rather than a particular noun.
Consider:
The council postponed the demolition, which gave residents more time to respond.
Here, which refers to the postponement. That decision gave residents additional time.
Compare:
The demolition plan, which had been revised twice, was finally approved.
In this sentence, which had been revised twice modifies the demolition plan itself.
Whole-statement which allows a writer to comment on a preceding event without starting another sentence.
This type of relative clause is supplementary and is normally introduced by a comma.
Relative Clause or Content Clause?
Not every clause beginning with that is relative.
Compare:
The announcement that the gallery would close caused concern.
The announcement that the spokesperson corrected caused concern.
In the first sentence, that the gallery would close explains what was announced. It is a content clause.
In the second, that the spokesperson corrected identifies the announcement. The spokesperson corrected the announcement, so that represents the object of corrected.
Another distinction involves what.
Incorrect: The proposal what the committee approved was expensive.
Correct: The proposal that the committee approved was expensive.
However, we can say:
What the committee approved was expensive.
Here, what the committee approved means roughly the thing that the committee approved. It functions as a noun-like construction rather than modifying an expressed noun.
Relative Clauses: Practice With Answers
1. Choose the Correct Relative-Clause Forms
A committee consulted a researcher. The researcher later received a grant.
Combine the statements using a relative clause identifying the researcher.
Possible answers:
The researcher who the committee consulted later received a grant.
The researcher whom the committee consulted later received a grant.
The researcher the committee consulted later received a grant.
All three are grammatical.
Who is common in everyday English, while whom is more formal. The relative pronoun may also be omitted because it represents the object of consulted.
2. Rewrite With a Fronted Preposition
Rewrite this sentence in a more formal style:
The organisation that the council provided funding to has expanded.
Answer:
The organisation to which the council provided funding has expanded.
The preposition to moves before which. The grammatical relationship remains the same.
3. Identify the Type of Shortening
Compare:
A. The article the editor requested is ready.
B. The article requested by the editor is ready.
Which uses an omitted relative pronoun, and which uses a participial construction?
Answer:
A contains a defining relative clause with an omitted object relative pronoun.
It could be written:
The article that the editor requested is ready.
B contains a past-participial modifier, corresponding closely to:
The article that was requested by the editor is ready.
The two shortened constructions have different internal structures.
4. What Does Which Refer To?
The committee extended the application deadline, which allowed more candidates to apply.
Does which refer to the deadline itself or to the extension?
Answer: It refers to the fact that the committee extended the deadline.
That action allowed more candidates to apply.
The relative clause comments on the preceding event rather than simply describing the noun deadline.
5. Can Whose Be Omitted?
The manager introduced the consultant whose recommendations had influenced the decision.
What relationship does whose express? Can it simply be removed?
Answer:
Whose recommendations refers to the recommendations made by or associated with the consultant.
The relative word whose expresses that relationship within the clause.
Removing it would leave:
The manager introduced the consultant recommendations had influenced the decision.
This is not a grammatical version of the intended sentence.
Unlike an optional object relative pronoun, whose cannot simply be omitted while leaving the rest of the construction unchanged.
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