Relative Pronouns (who/whom/which/that)

You've finished the email. You read the line back: "Please forward this to the colleague who handles invoices." Then you stall. Who or whom? Later, drafting a report, you hit: "the policy which…" or "the policy that…"? And do you need a comma there, or not?

Here's the thing — relative pronouns are small words doing heavy lifting: who, whom, whose, which, that. Get them slightly wrong and your writing "sounds off" without anyone being able to say quite why. Get the pattern straight and a whole family of everyday writing — CV lines, emails to landlords, reports to clients — starts to feel properly under control.

Nobody's born knowing this. Even fussy editors argue about corners of it, and ordinary speech has quietly dropped "whom" almost everywhere. The good news is you don't need a grammar degree to sort this — just a clear map of what each word does, when a clause is essential rather than optional, and how formal the room you're writing for actually is.

Before you read on, here's where we're heading. By the end of this article, you'll be able to: - Use who, whom, whose, which, and that with a working method rather than a guess. - Distinguish restrictive from non-restrictive relative clauses, and punctuate them correctly. - Make a defensible that/which choice in professional and formal writing. - Use whose confidently with inanimate antecedents, and recognise pied-piping for formal register. - Know exactly what this article deliberately leaves out (the who's/whose spelling trap) and where to go for it.

Beginner (Foundation)

A relative pronoun introduces a relative clause — a clause that identifies or describes a noun that's already been named. That earlier noun is the antecedent.

"The contractor who fitted the kitchen left his tools behind."

• Antecedent: "contractor"
• Relative pronoun: "who"
• Relative clause: "who fitted the kitchen"

The clause sits right after the noun and adds information without you having to start a new sentence. That's the entire job.

The core set, and their typical roles:

• who — people, as the subject: "the neighbour who called."
• whom — people, as the object, or after a preposition: "the neighbour whom we thanked."
• whose — possession: "the neighbour whose fence fell."
• which — things and animals, and non-restrictive (bonus) clauses: "the report which arrived late."
• that — people or things, in essential (restrictive) clauses: "the report that arrived late."

A quick habit worth building: turn the relative clause into its own mini-sentence about the antecedent. "Who called" → "he called" → subject → who. "Which arrived late" → "it arrived late" → thing → which or that.

And notice, even at this basic level, that some clauses are essential to identifying who or what you mean, and some are just bonus extras. That split runs the whole of the rest of this article — commas, that vs which, all of it. For now, just feel the difference:

Essential: "Tickets that are non-refundable cannot be exchanged." (which tickets? — the non-refundable ones)
Extra: "My tickets, which are non-refundable, cannot be exchanged." (we already know which tickets; the non-refundable bit is just a fact)

Quick recap: - Relative pronouns attach a describing clause to a named noun — the antecedent. - Core set: who, whom, whose, which, that. - Who/whom/whose mainly go with people; which/that with things — that covers people too when the clause is essential. - Essential vs extra information is the structural idea everything else in this article builds on.

Intermediate (Development)

Restrictive vs non-restrictive

A restrictive (defining) relative clause narrows the identity of the antecedent — you need it to know exactly who or what is meant. No commas.

"Applicants who miss the deadline will not be considered."

Only that subset of applicants. Remove the clause and the sentence's meaning changes.

A non-restrictive (non-defining) clause adds extra information about an antecedent that's already clearly identified. Use a comma pair — or a single comma if the clause ends the sentence. You could delete it without losing the identity of who or what is meant.

"Our HR manager, who joined last May, rewrote the onboarding pack."

There's only one HR manager here. The joining date is a useful aside, and the commas signal exactly that.

This isn't pedantry. In workplace writing, misplaced commas can accidentally imply that all applicants missed the deadline, or that all the servers need rebooting, when you only meant some of them. That's how a perfectly polite email ends up causing genuine confusion.

That and which

A workable, professional pattern for UK writing (and one widely taught in US style guides too):

Non-restrictive, things: which, always with commas.

"The main archive, which is on the third floor, closes at five."

Restrictive, things: prefer that — or which without a comma, if your house style permits it.

"Please archive the files that are older than three years."

US editorial style (and many US corporate style sheets) tends to be firmer about this: that for restrictive, which strictly reserved for non-restrictive. Careful UK editing still accepts restrictive which without a comma, but that-for-restrictive is clean, learnable, and rarely causes trouble. If you're writing to a US client or following a US style sheet, default to the stricter split.

For people in restrictive clauses, both that and who are grammatical. Prefer who when you want a human tone — CVs, references, staff announcements — and reserve that for moments that feel more formal or legalistic.

Who vs whom — a test that actually works

Who = subject of the relative clause.
Whom = object of the verb, or object of a preposition.

Replace the relative pronoun with he/she or him/her in a stand-alone version of the clause:

"The manager who approved the budget" → "she approved" → subject → who.
"The manager whom we briefed" → "we briefed her" → object → whom.
"The client to whom we sent the quote" → "we sent the quote to him" → whom.

Let's be honest — I still run that little substitution test myself when a sentence gets long enough to lose the thread. In speech, and in most Slack messages, who has largely absorbed whom, and nobody minds. But in a job application, a board paper, or a formal complaint, using whom correctly still signals care and control. Using it incorrectly is worse than simply defaulting to who — so only reach for it when the test gives you a clear answer.

Pro-Tip:
Genuinely unsure whether "whom" is worth the risk? Rephrase to dodge it entirely: "The manager we briefed" works perfectly well without any relative pronoun at all.

Whose with things, not only people

Whose marks possession — for people or things.

"The colleague whose shifts swapped."
"The firm whose valuation doubled."
"A process whose bottleneck is advertising approvals."

This is entirely standard. The old classroom myth that whose is "only for people" simply isn't true. You can also write "of which" ("a process the bottleneck of which…"), but it usually sounds far stiffer. Use whose unless formality genuinely demands the alternative.

One reminder, and then we move on: whose is not who's. Who's means "who is" or "who has" — a completely different word that happens to sound the same. That entire homophone trap belongs to H2.4; if autocorrect keeps catching you out on it, that's the article to go to, and we won't re-teach it here.

Common Mistake:
Using who where you need the possessive form. ✗ "The supplier who invoice arrived late…" ✓ "The supplier whose invoice arrived late…" (or rephrase: "the supplier that sent the late invoice").

Pro-Tip:
When editing your own writing at speed, scan every who/which clause for one question: subset selector, or stitched-on fact? Subset = no commas. Stitched-on fact about something already known = commas.

Quick recap: - Restrictive clauses identify (no commas); non-restrictive clauses comment (commas) — mixing them up changes your actual meaning. - Prefer that for restrictive clauses about things; which plus commas for non-restrictive ones. - Who is the subject form, whom the object form — test with he/him or she/her. - Whose works fine with inanimate antecedents; "of which" is the stiffer formal alternative. - The who's/whose spelling confusion is a separate issue, covered fully in H2.4.

Advanced (Mastery)

Pied-piping and preposition placement

When the relative pronoun is governed by a preposition, you have two layouts available.

Stranding (preposition left at the end of the clause):

"the budget we argued about" → "the budget which/that we argued about"
"the chair we reported to"

Pied-piping (preposition fronted, travelling with the relative pronoun):

"the budget about which we argued"
"the chair to whom we reported"

Pied-piping takes its name from the way the preposition is led along with the relative pronoun, rather like children following the Pied Piper. It reads as more formal — genuinely useful in contracts, board papers, academic writing, and anywhere a stranded preposition would feel a touch too casual. Stranding is fully grammatical, and often clearer, in everyday email and web copy. The choice is about matching the room, not about right and wrong.

When you can — and can't — omit the relative pronoun

In restrictive object clauses, English happily drops the pronoun:

"The candidate (whom/who) we interviewed on Tuesday…"
"The quote (that) you approved…"

You cannot omit a subject relative:

✗ "The candidate impressed the panel got an offer."
✓ "The candidate who impressed the panel got an offer."

Nor can you omit the pronoun in a non-restrictive clause:

✓ "The second quote, which arrived after five, was unusable."
✗ "The second quote, arrived after five, was unusable."

Register, collectives, and a few genuine edge cases

• Collective nouns: "the board who decided" treats the board as a group of people; "the board which decided" treats it as a single institution. Pick a lens and stay consistent through a document.
• Animals and personified brands: who for a much-loved family dog or a deliberately personified brand voice; which/that in technical or detached writing.
• "One of the … who/that …" agreement: "She is one of the managers who sign off expenses" — the verb agrees with managers (plural), not one, because the relative clause looks back to the whole group. This one still trips people up, myself included, when the sentence gets long.
• Sentential which: "The server went down overnight, which delayed the release." Here which refers back to the whole preceding idea, not to a single noun — a recognised and useful pattern, but one to ration. More than one per paragraph starts to feel foggy.
• Stacking: "the report that the team that you led produced" is technically legal English and thoroughly unkind to your reader. Split it into two sentences.

If you want to go further into how relative clauses fit into more elaborate sentence architecture — reduced relative clauses, free relatives, and how clauses nest inside one another — that full treatment belongs to the forthcoming Clauses pillar for this library. This article stays deliberately focused on pronoun choice and the restrictive/non-restrictive machinery behind it.

Common Mistake:
Punctuating a restrictive idea as if it were non-restrictive: "Staff, who work weekends, receive a premium." As written, that claims all staff work weekends. For the subset meaning you actually want: "Staff who work weekends receive a premium."

Pro-Tip:
On anything formal and important — a client-facing report, a contract clause — write the sentence both ways, stranded and pied-piped ("the issue I'm responsible for" / "the issue for which I'm responsible"), and read both aloud. Keep the one that sounds like a confident human, not a legal document pretending to be one — unless a legal document is genuinely what you're writing.

Quick recap: - Pied-piping ("for which," "to whom") lifts formality; stranding the preposition is natural in most everyday prose. - You can drop a relative pronoun only when it's the object of a restrictive clause — never the subject, never in a non-restrictive clause. - Collective nouns, animals, and sentential which are style decisions — stay consistent and don't overuse the last one. - Heavy stacking of relative clauses is a sign to write two sentences instead of one.

UK vs US Usage

The grammar underneath relative pronouns is identical in UK and US English. The differences that actually matter for working adults are about house style and how strictly the conventions get enforced.

Restrictive that vs which. US style manuals — and a great many US corporate style guides — often enforce a firm rule: that for restrictive clauses, which reserved strictly for non-restrictive ones. UK usage, from newspapers to the civil service to general publishing, more readily accepts restrictive which without a comma, though many UK editors still prefer that for the sake of clarity. If you're submitting work under a US house style, follow the stricter rule without argument. For UK work, either pattern is generally accepted — the only real requirement is consistency within a single document.

Whom. Rare in conversation on both sides of the Atlantic. Retained in formal writing at broadly similar rates in both varieties — there's no special claim either side can make on it.

Whose with inanimate nouns. Fully accepted in both UK and US English. Not a dialect fight worth having.

Spelling in the surrounding sentence, not the pronouns. Organisation [US: organization], programme [US: program, for general use], centre [US: center] shift with your audience; the relative pronouns themselves — who, whom, whose, which, that — never change spelling between the two varieties.

The practical bottom line: get the relative clause itself right — restrictive or not, subject or object — and then tune that/which and pied-piping to whichever style sheet your reader expects. That's a matter of craft, not a law of nature to defy.

Quick recap: - US style guides tend to enforce the that/which split strictly; UK usage is more relaxed about restrictive which. - Whom is fading from speech on both sides but still expected in formal written English in both. - Whose with things is accepted everywhere; the pronouns themselves don't change spelling between UK and US English.

Key Takeaways

• Relative pronouns (who, whom, whose, which, that) attach an identifying or describing clause to a noun, keeping your writing efficient.
• Restrictive clauses (no commas) select which person or thing you mean; non-restrictive clauses (commas) simply comment — mixing them up changes your actual claim.
• Who is the subject form, whom the object form; test with he/him or she/her.
• Whose works fine with things, not just people; pied-piping ("to whom," "for which") is a formal tool for register, not an obligation.
• The who's/whose spelling trap and the full architecture of relative clauses both belong elsewhere — see the internal links below.

Check Your Understanding

1. Choose the better form for a formal report, treating the committee as a single institution: "the committee (who/which) approved the bid."
2. Add or remove commas as needed (there is only one landlord in this story): "Our landlord who owns three other flats refused the request."
3. Rewrite using the correct relative pronoun, and offer a pied-piped alternative: "She's the auditor I always send the draft to."
4. Is this sentence correct? If not, fix it: "The process who's first stage failed needs redesign."
5. Is this clause restrictive or non-restrictive, and is the punctuation correct? Fix it if not: "Vehicles, that block the exit, will be towed."

Answer key

1. which — treating the committee as a single institution suits which; who would push toward a "people" reading.
2. Non-restrictive, since there's only one landlord: "Our landlord, who owns three other flats, refused the request."
3. "She's the auditor to whom I always send the draft." (Or, keeping it informal: "the auditor I always send the draft to.")
4. Incorrect — "who's" should be "whose": "The process whose first stage failed needs redesign."
5. Restrictive (it identifies which vehicles), so no commas, and that is the right choice: "Vehicles that block the exit will be towed."

Internal Links

• H2.1 — Pronouns: the foundations (personal, subject and object pronouns)
• H2.2 — Possessive pronouns and determiners (background for whose)
• H2.4 — Whose vs who's (the homophone trap — full treatment there, not repeated here)
• H7.2 — Subordinators (how relative clauses sit among the wider family of subordinate clauses)
• Forward link — the future Clauses pillar (full architecture of relative clauses, reduced relatives, and free relatives)