“who” vs. “whom”
Use "who" wherever "he" or "she" would fit as the answer, and "whom" wherever "him" or "her" would fit — subject gets "who," object gets "whom."
who
"Who" is the subject form of this pronoun, used when the pronoun is doing the action of the verb ("who called you?" — who did the calling). "Who" comes from Old English "hwa," the nominative (subject) case form of the interrogative/relative pronoun system, a case distinction English has largely abandoned everywhere else except in this one pronoun pair.
whom
"Whom" is the object form, used when the pronoun is receiving the action rather than performing it ("whom did you call?" — the calling is being done to whom). "Whom" descends from Old English "hwam," the dative (object) case form of the same pronoun — a genuine grammatical case survival from a period when English marked far more nouns and pronouns for case than it does today.
The real distinction
English used to mark case (subject vs. object form) on far more words than it does now — modern English keeps this distinction alive only in personal pronouns (I/me, he/him, she/her, they/them) and, on paper, in who/whom. The practical test: if you can answer the implied question with "he" or "she," use "who"; if the natural answer is "him" or "her," use "whom" ("who called?" — "he called," so "who"; "whom did you call?" — "I called him," so "whom"). In casual spoken English, "whom" has been fading for well over a century, and many fluent native speakers now use "who" in virtually every context, reserving "whom" only for formal writing or fixed phrases like "to whom it may concern." Linguists studying language change generally treat this as a case system nearing the end of a very long, slow collapse — English has already lost case marking almost everywhere else, and "whom" is one of the last visible holdouts, alongside the personal pronouns. Style guides differ on how strictly to enforce "whom": some treat a missing "whom" in formal writing as a real error worth catching, while others now describe insisting on "whom" in casual writing as needlessly stiff, since the form sounds noticeably formal, even old-fashioned, to many contemporary ears. Overcorrection is also common — writers who know "whom" sounds more careful sometimes insert it in subject position by mistake ("whom is calling?"), a hypercorrection error that's arguably more jarring to careful readers than simply using "who" everywhere. The trickiest real-world cases are sentences where the pronoun's role gets buried inside a longer clause, such as "whom do you think called?" — a construction many careful writers get wrong, because "whom" here actually belongs to the embedded clause "[who] called," where it's functioning as a subject, so the grammatically correct form is in fact "who do you think called?" despite "whom" looking more formal. Formal written English — legal documents, academic prose, and traditionally edited journalism — still enforces the who/whom distinction fairly consistently, which means the rule is worth knowing even for writers who'd never use "whom" in casual conversation, since it can still mark a document as carelessly proofread if a reader who does track the distinction notices a slip.
Examples with “who”
- Who left the door unlocked?
- She's the one who solved the puzzle.
- Who is bringing dessert tonight?
- The witness who testified seemed nervous.
- Who wrote this report?
- I wonder who will win the award.
- The neighbor who called the police saw everything.
- Who's responsible for this decision?
Examples with “whom”
- To whom should I address this letter?
- Whom did the committee choose for the award?
- She's the colleague whom I trust most.
- Whom did you invite to the dinner?
- The client whom we met yesterday signed the contract.
- For whom is this gift intended?
- Whom did the manager ultimately hire?
- The professor whom I admire most retired last year.
Memory trick
Both "whom" and "him" end in m — a small spelling hook that ties the object-form pronoun to its object-form partner. If rephrasing the sentence with "he" sounds natural, you need "who"; if rephrasing with "him" sounds natural, you need "whom," even if the resulting sentence order feels a little awkward compared to the original question or clause.