Relative pronouns connect a dependent relative clause to a noun or pronoun in a main clause while performing a grammatical role inside that clause. The main relative pronouns are who, whom, whose, which, and that. Choosing among them depends on the antecedent, the pronoun’s role, whether the clause is essential, and the punctuation required.
Key Facts at a Glance
A relative pronoun refers back to an antecedent and introduces a relative clause.
Who usually functions as the subject for a person; whom functions as the object.
Whose expresses possession and can refer to people, animals, and things.
That normally introduces a restrictive clause and never follows a comma.
Non-restrictive clauses are set off with commas and generally use who, whom, whose, or which.
A relative pronoun can be omitted when it is the object, but not when it is the subject.
What Are Relative Pronouns?
Relative pronouns are connecting words that do two jobs at once: they refer to an antecedent and introduce a dependent clause that modifies it. In The scientist who discovered the vaccine won an award, who refers to the scientist and acts as the subject of discovered the vaccine.
A relative clause cannot normally function as a complete sentence by itself. The clause who discovered the vaccine depends on The scientist won an award, while the full sentence combines both ideas without repeating the scientist. Relative pronouns therefore encode reference, clause connection, and grammatical case.
How does a relative clause work?
A relative clause contains a gap whose meaning is supplied by the antecedent. Compare these sentences:
- Separate: The researcher published a paper. The researcher led the trial.
- Combined: The researcher who led the trial published a paper.
The relative clause is who led the trial. The understood subject of led is the researcher. In The paper that the researcher published won an award, that represents the object of published, because the researcher is the subject.
The position of the gap matters more than the noun’s position in the main clause. In I thanked the researcher who led the trial, researcher is the object of thanked, but who is still the subject inside the relative clause.
Which Relative Pronoun Should You Use?
The correct relative pronoun depends first on meaning, then on grammatical role and clause type. Use who for a person functioning as subject, whom for a person functioning as object in formal contexts, whose for possession, which for many nonhuman references, and that for many restrictive clauses.
| Pronoun | Typical reference | Role in relative clause | Example |
|---|---|---|---|
| who | Person or people | Subject | The engineer who designed the bridge received an award. |
| whom | Person or people | Object | The engineer whom we hired starts Monday. |
| whose | Person, animal, or thing | Possessive determiner | The company whose servers failed issued a notice. |
| which | Thing, animal, or whole clause | Subject or object | The device, which uses less power, costs $80. |
| that | Person, animal, or thing | Subject or object | The report that changed policy was published in June. |
Who: the subject form
Use who when the referenced person performs the action in the relative clause. In The teacher who explained the rule was patient, who performs explained. The same choice works with plural antecedents: The students who completed the test left early.
In ordinary speech, who is also common in places where formal grammar traditionally expects whom, especially in questions and informal writing. That does not make every use interchangeable in edited prose. The subject test remains reliable: replace the relative pronoun with he, she, or they.
Whom: the object form
Use whom when the referenced person receives an action or follows a preposition in formal English. In The candidate whom the panel selected accepted the offer, the panel performs selected, and whom receives it.
A quick test is to replace the pronoun with him, her, or them:
- The panel selected them.
- Therefore: the candidate whom the panel selected.
Many speakers use who instead, particularly when the preposition is left at the end: Who did you invite? Formal writing may prefer Whom did you invite? or To whom did you send the letter? The version with whom is precise, but forcing it into every conversational sentence can sound unnatural.
Whose: the possessive form
Whose shows that the antecedent possesses, owns, includes, or is associated with something. It can refer to people, animals, organizations, and physical objects:
- The author whose novel won the prize gave a reading.
- The dog whose collar was missing escaped.
- The database whose index was corrupted required restoration.
Unlike who and whom, whose is followed by a noun or noun phrase, such as whose book, whose data, or whose roof. Do not confuse relative whose with interrogative whose in a question. The form is identical, but the grammatical function differs.
How Do Restrictive and Non-Restrictive Clauses Differ?
A restrictive relative clause identifies which person or thing the writer means, so it is not separated by commas. A non-restrictive relative clause adds information about an already identified noun, so commas mark its beginning and end.
| Clause type | Meaning after deletion | Punctuation | Common pronouns | Example |
|---|---|---|---|---|
| Restrictive | Meaning becomes less specific | No commas | who, whom, whose, which, that | The files that contain errors need review. |
| Non-restrictive | Main reference remains identifiable | Pair of commas | who, whom, whose, which | The files, which contain errors, need review. |
| Restrictive with proper name | Usually unnecessary because name identifies referent | Usually no clause | who, whose, which | Dr. Lee, who leads the lab, arrived. |
| Sentence-level comment | Clause comments on the preceding idea | Comma before clause | which | The trial ended early, which surprised investors. |
When should you use that?
Use that when the relative clause is restrictive and identifies the noun under discussion. That works for people, animals, and things in many varieties of English:
- The employee that reported the fault received support.
- The key that opens the cabinet is missing.
- The medication that reduced symptoms caused no serious reaction.
Many formal American style guides recommend that for restrictive clauses referring to things and which for non-restrictive clauses. Actual usage is broader, especially in British English, where restrictive which is standard. The central punctuation rule is stable: that does not introduce a non-restrictive clause and should not appear after a comma.
When should you use which?
Use which for a nonhuman antecedent when the clause supplies additional information: The bridge, which opened in 1928, remains in service. The comma tells the reader that the bridge is already identified and that its opening date is supplementary.
Restrictive which is also grammatical in many contexts: The bridge which opened in 1928 remains in service. In formal American prose, many editors would choose that if the clause identifies one bridge among several. Style consistency matters more than treating the regional preference as a universal grammatical law.
Why do commas change the meaning?
Commas signal whether the relative clause narrows the noun’s reference. Employees who work remotely receive the allowance refers to a subset. Employees, who work remotely, receive the allowance presents remote work as information about all the employees.
The second sentence may be factually unintended, especially when the antecedent is plural. Punctuation therefore changes scope, not merely visual rhythm. The deletion test helps, but context decides: if the noun is already uniquely identified, a non-restrictive clause is usually appropriate.
Can You Omit a Relative Pronoun?
A relative pronoun can be omitted when it functions as the object of the relative clause, but it cannot be omitted when it functions as the subject. The omission is common in conversational and concise writing.
| Full form | Omitted form | Why omission works |
|---|---|---|
| The book that I bought is rare. | The book I bought is rare. | That is object of bought. |
| The person whom we contacted replied. | The person we contacted replied. | Whom is object of contacted. |
| The book that changed my view is old. | Not: The book changed my view is old. | That is subject of changed. |
| The manager who approved the request called. | Not: The manager approved the request called. | Who is subject of approved. |
To test omission, inspect the clause after the relative pronoun. If another noun or pronoun already performs the verb’s action, the relative pronoun is probably an object and may be omitted. In the report that analysts reviewed, analysts is the subject, so that is the object.
Omission can create ambiguity when several nouns could fill the gap. Retain the pronoun when the sentence becomes difficult to parse, especially in legal, technical, or safety instructions.
Where Do Relative Adverbs Fit?
Where, when, and why are relative adverbs because they introduce clauses connected to an antecedent while expressing place, time, or reason. They are not pronouns: where expresses location, when expresses time, and why expresses reason.
| Relative adverb | Antecedent | Meaning | Example |
|---|---|---|---|
| where | Place | In or at which | The lab where she works closes at six. |
| when | Time | During which | The year when the merger occurred was difficult. |
| why | Reason | For which | The reason why he resigned remains private. |
| wherein | System, document, or situation | In which | The policy wherein access is restricted is outdated. |
Relative adverbs often have equivalent prepositional forms:
- The lab where she works = The lab in which she works
- The year when the merger occurred = The year in which the merger occurred
- The reason why he resigned = The reason for which he resigned
Why is often unnecessary after the reason: The reason he resigned remains private is concise and grammatical. The phrase the reason why is widely accepted, so removing why is a stylistic choice rather than a universal correction.
Who, Whom, Which, and That: What Is the Practical Difference?
The practical difference is a combination of reference, case, clause type, and register. Who and whom distinguish subject from object most clearly; which and that often distinguish supplementary information from identifying information.
| Decision question | Preferred form | Example | Register or condition |
|---|---|---|---|
| Is a person doing the action? | who | The analyst who found the error spoke up. | All registers |
| Is a person receiving the action? | whom or informal who | The analyst whom we hired starts today. | Whom is formal |
| Does the clause show possession? | whose | The analyst whose report was correct stayed late. | All registers |
| Does a thing need identifying information? | that or restrictive which | The file that contains the key is encrypted. | That is common in US formal prose |
| Does a thing need extra information? | which | The file, which contains the key, is encrypted. | Commas required |
| Does a preposition precede the form? | whom for people, which for things | The person to whom I wrote; the system through which data passed | Formal style |
An important practitioner rule is to decide clause type before choosing between that and which. Writers often make the mistake in reverse, selecting a familiar word and adding punctuation afterward. Meaning must control punctuation.
What Are Common Relative-Pronoun Errors?
Relative-pronoun errors usually involve case, punctuation, attachment, or a mismatch between the antecedent and the clause. The fastest correction method is to isolate the relative clause, identify its missing role, and then reconnect it to the nearest logical antecedent.
Error 1: Using a comma before that
Incorrect: The laptop, that I bought yesterday, is slow.
Correct: The laptop that I bought yesterday is slow.
The clause is restrictive if it identifies which laptop is meant, and that cannot introduce a non-restrictive clause. If the writer means one already identified laptop, use which with commas: My laptop, which I bought yesterday, is slow.
Error 2: Choosing whom as the subject
Incorrect: The consultant whom recommended the change left.
Correct: The consultant who recommended the change left.
The consultant performs recommended, so the subject form who is required. Use whom in the consultant whom the board consulted, where the board performs consulted.
Error 3: Creating a dangling relative clause
Unclear: We gave treats to the dogs that were baked this morning.
The grammar appears to attach that were baked to dogs, producing an absurd interpretation. Rewrite as We gave the dogs treats that were baked this morning, placing the relative clause next to treats, its intended antecedent.
Error 4: Using a redundant pronoun
Incorrect: The report that I reviewed it contained errors.
Correct: The report that I reviewed contained errors.
The relative pronoun already fills the object position. Keeping it creates two objects for reviewed. A separate pronoun can appear in the main clause, as in The report that I reviewed, it contained errors, only in special spoken or dialectal structures, not standard edited prose.
Error 5: Confusing that and what
That refers back to an expressed antecedent: The claim that the test failed was disputed. What means approximately the thing that and normally has no separate antecedent: What the test revealed was unexpected.
The forms are not interchangeable. The claim what the test revealed is incorrect in standard English because claim already supplies an antecedent for the clause.
How Should You Choose a Relative Pronoun in Five Steps?
Choose a relative pronoun by identifying the antecedent, locating the gap, deciding whether the information is essential, checking punctuation, and reading the complete sentence aloud. This five-step process takes about 20-30 seconds for an ordinary sentence and catches most errors.
- Circle the antecedent. Identify the noun the clause describes, such as engineer, device, files, or reason.
- Locate the missing role. Ask whether the antecedent performs the relative-clause verb, receives it, or possesses the following noun.
- Select the form. Choose who for a human subject, whom for a formal human object, whose for possession, and which or that for nonhuman references.
- Test essentiality. Delete the clause. If the identity changes, omit commas. If the noun remains clearly identified, use commas and avoid that.
- Check attachment and agreement. Place the clause beside its antecedent and ensure the verb agrees with the noun inside the clause.
For example, in The sensors that detected smoke triggered the alarm, sensors is the antecedent, the sensors perform detected, and the clause identifies a subset. That is acceptable, no commas are used, and the plural verb detected agrees with sensors.
How Do Relative Pronouns Work in Special Cases?
Relative pronouns become less predictable with animals, organizations, compound antecedents, proper nouns, and prepositions. Meaning and register should guide the choice rather than a rigid human-versus-object rule.
Animals
Use which or that for animals treated as nonhuman objects: The horse that won the race was retired. Use who when the animal is named, personified, or treated as an individual: Milo, who sleeps by the door, is seven.
The choice expresses perspective as well as grammar. Veterinary, scientific, and legal writing may use who for companion animals or sentient subjects, while technical descriptions commonly use which.
Organizations and institutions
An organization may take which or that, depending on clause type: The agency that issued the permit changed its policy; The agency, which issued the permit, changed its policy. In some varieties of English, an organization may take who when the members are foregrounded, but which remains the safer formal default for the institution itself.
Compound antecedents
When the antecedent contains two nouns, make the reference unmistakable: The manager and assistant who approved the invoice signed the form may mean both people or only the assistant. Rewrite as The manager and the assistant who approved the invoice signed the form if only the assistant approved it, or The manager and assistant, who approved the invoice, signed the form if both did.
Prepositions
Formal English places the preposition before whom or which: the client for whom we prepared the report; the process by which the sample was tested. Informal English often strands the preposition: the client who we prepared the report for.
Do not use that immediately after a fronted preposition. The process through that the sample passed is incorrect. Use through which, or restructure the sentence as the process that the sample passed through.
How Can You Practice Relative Pronouns Efficiently?
Most learners can understand the basic forms in one focused session of 60-120 minutes, while reliable control of commas, omission, and formal case usually requires 1-2 weeks of deliberate editing. Practice works best when each exercise isolates one decision instead of mixing every rule in a single worksheet.
Use this progression:
- Combine pairs of sentences with who, which, that, or whose.
- Label each relative pronoun as subject, object, or possessive.
- Add or remove commas according to the intended meaning.
- Rewrite object relatives with and without the pronoun.
- Edit authentic emails, reports, or essays for attachment and ambiguity.
- Read formal alternatives aloud and choose the version appropriate to the audience.
Free practice is available through university writing centers, including the Purdue Online Writing Lab, and reference grammars such as The Cambridge Grammar of the English Language provide deeper analysis. Automated grammar tools can flag punctuation patterns, but they cannot reliably determine whether a clause is factually restrictive. A human reader must decide the intended meaning.
FAQ About Relative Pronouns
Is “that” a relative pronoun?
That is a relative pronoun when it introduces a relative clause and fills a subject or object role, as in the book that changed my thinking. It also has other grammatical uses, including demonstrative determiner, demonstrative pronoun, and complementizer. The surrounding clause determines which function applies.
Can “which” refer to a person?
Standard edited English generally uses who or whom for people and which for things. Which can refer to a group, organization, or animal when the writer treats the antecedent as a nonhuman entity, but the person which called is not standard in contemporary formal English.
Is “whom” becoming obsolete?
Whom remains active in formal writing, especially after prepositions, as in to whom it may concern. In informal speech, who increasingly replaces whom, and many speakers avoid the distinction. Writers should preserve whom when it improves precision or matches a formal register, not insert it mechanically.
What is the difference between a relative pronoun and a conjunction?
A relative pronoun refers to an antecedent and performs a role inside its clause. A conjunction links clauses but does not replace a noun inside the second clause. In the book that I read, that represents the object of read; in I left because it was late, because only expresses the relationship between clauses.
Are commas always required before which?
Commas are required when which introduces a non-restrictive clause, as in The printer, which is ten years old, still works. Restrictive which can appear without commas, particularly in British English and some technical styles: The printer which uses toner is faster. Meaning and the selected style guide should control the decision.
Can a relative clause begin with “where” after any place noun?
Where works naturally with locations that permit an in, at, or on relationship: the room where we met. It may sound awkward with nouns that are not genuine locations. Use in which, at which, or a rewritten sentence when the spatial relationship is unclear.
The Bottom Line
Relative pronouns connect a modifying clause to an antecedent while representing the antecedent’s role inside that clause. Use who for a person acting as subject, whom for a formal human object, whose for possession, which for many nonhuman or supplementary clauses, and that for many restrictive clauses without commas.
The most dependable editing sequence is simple: identify the antecedent, find the missing subject or object, decide whether the clause restricts meaning, apply the correct punctuation, and check that the clause sits beside the noun it describes. Relative pronouns become manageable when meaning determines grammar instead of memorized word substitutions.
