Who vs. Whom
Who and whom mark the same distinction English pronouns make elsewhere — subject versus object — but because English mostly abandoned case marking on nouns centuries ago, this leftover distinction on one pronoun pair feels unfamiliar and gets flattened in casual speech, where 'who' increasingly covers both roles. The underlying rule, though, is exactly the same logic as choosing he versus him, or she versus her.
The core rule: subject vs. object
Use who wherever you'd use he, she, or they — as the subject of a verb: Who called? (He called.) Use whom wherever you'd use him, her, or them — as the object of a verb or preposition: Whom did you call? (You called him.) To whom should I address this? (I should address this to her.) This substitution test — swap in he/she/they for who, or him/her/them for whom, and see which pronoun form the sentence actually wants — resolves the overwhelming majority of who/whom uncertainty without needing to diagram the sentence.
Whom after a preposition
Whom is required directly after a preposition in formal writing: to whom, for whom, with whom, by whom. This is one of the more reliable places to spot the rule in the wild, since prepositions almost never take a subject-form pronoun (nobody says 'to he' or 'for she'), which makes 'to who' feel wrong to careful readers even when casual speech tolerates it: To whom it may concern is the fixed, still-standard formal opening precisely because of this rule.
Embedded clauses make the test harder
The substitution test gets trickier inside embedded clauses, where the who/whom decides its role within its own clause, not the sentence as a whole: Give it to whoever asks for it. Here 'whoever' is the subject of 'asks,' even though the whole clause is the object of 'to' — the pronoun's case tracks its job inside its own clause, not the larger sentence's structure, which is why 'whomever' would be wrong here despite following a preposition. Isolating the embedded clause and asking who's doing what inside it, separately from the outer sentence, is the reliable fix.
Why 'whom' is disappearing from speech
Case-marked pronouns generally survive longest in a language's most frequent, most basic pronouns (I/me, he/him, she/her) and fade first from its least frequent or more formal-register forms — whom fits that second category, appearing mostly in questions and relative clauses rather than everyday subject-verb sentences. Linguists studying the decline note that 'whom' has been retreating from ordinary spoken English for well over a century, surviving mainly in set phrases (to whom it may concern) and in writing registers where a more formal, deliberate tone is wanted.
Is using 'who' for 'whom' actually wrong?
In casual speech, 'Who did you call?' is now overwhelmingly standard and unremarkable, even among careful speakers, and most descriptive linguists treat the who/whom distinction in speech as a largely dead feature outside fixed phrases and highly formal registers. In formal written prose — legal documents, academic writing, official correspondence — maintaining the distinction is still expected, and using 'who' where 'whom' is called for can read as a small but noticeable lapse to an audience trained to notice it, which is why the rule remains worth knowing even for writers who never bother with it in speech.
Whoever vs. whomever
The same subject/object logic extends to whoever and whomever, with the same substitution test: use whoever where he/she/they would fit, whomever where him/her/them would fit. Because these words usually appear in embedded clauses, the same embedded-clause caution above applies — check the pronoun's role inside its own clause, not the sentence overall.
Who/whom in relative clauses modifying a noun
The same test applies when who or whom introduces a clause describing a noun: The manager who approved the request left the company (who is the subject of approved — she approved it). The manager whom the board dismissed left quietly (whom is the object of dismissed — the board dismissed him). Because these clauses sit right after the noun they describe, it's easy to lose track of the embedded clause's own internal subject and object, which is exactly why isolating just the relative clause and running the he/him substitution on it alone, ignoring the rest of the sentence, remains the most reliable method.
A note on hypercorrection
Because many speakers have absorbed a vague sense that 'whom' sounds more correct or formal, 'whom' sometimes gets inserted in places that actually call for who, producing sentences like 'Whom shall I say is calling?' (wrong — the clause needs a subject for 'is calling,' so it should be 'Who shall I say is calling?'). This kind of overcorrection is common enough that some usage guides consider misapplied whom nearly as frequent an error as misapplied who, which is a good reason to run the actual substitution test rather than trusting a gut sense that whom simply sounds fancier or safer.
Whom in formal written correspondence
Formal letters, legal filings, and academic prose are where the who/whom distinction is most consistently expected and most noticeably broken when it's wrong. 'To whom it may concern' persists as a fixed formal opening precisely because it's frozen in a register where the object-of-preposition rule is still actively enforced by convention, even though almost nobody would use 'whom' this way in a casual spoken sentence. Job application letters, official complaints, and contract language are the genres where getting this distinction wrong is most likely to be noticed by a reader trained to expect it, which is one practical reason to keep the rule in your toolkit even if you rarely use 'whom' in ordinary conversation.
How the distinction is taught versus how it's actually used
Traditional grammar instruction presents who/whom as a fixed, binary rule with no exceptions, but corpus studies of actual published and spoken English show a much messier reality: 'whom' has been declining in frequency for well over a century, and even highly educated speakers routinely use 'who' in contexts a strict grammarian would flag as calling for 'whom,' particularly in questions ('Who did you invite?' rather than the technically stricter 'Whom did you invite?'). This gap between the taught rule and the observed usage is one of the more well-documented examples in English of a grammatical distinction persisting in formal writing standards well after it has substantially eroded in everyday speech.
Related pronouns that follow the same logic
The same subject/object case distinction that separates who from whom also separates I/me, he/him, she/her, we/us, and they/them — English just happens to preserve it more visibly and more consistently in those more frequent pronoun pairs than in who/whom. If the who/whom test feels abstract, it can help to notice that nobody has trouble choosing between 'he called' and 'I called him' — the who/whom choice is doing exactly the same job, just on a pronoun pair that's fading from everyday use faster than its more common cousins.
A common test sentence to practice on
Try: '___ do you think will win the award?' Here, despite the pronoun appearing to sit in an object-like position right after 'do you think,' it's actually the subject of 'will win' (compare: 'he will win,' not 'him will win'), so 'who' is correct: Who do you think will win the award? This is one of the trickiest patterns in the whole system, because the inserted phrase 'do you think' visually separates the pronoun from the verb it's actually the subject of, tempting writers to treat the pronoun as if it belongs to the inserted phrase instead.
Whom in headlines and edited prose today
Major newspapers and style-conscious publications still enforce the who/whom distinction in written copy, even though their own reporters would rarely use whom in casual conversation — this split between spoken and edited-written registers is one of the clearest illustrations of how a grammatical form can survive in one register of a language while fading from another. Copy editors trained on this rule catch it reflexively, which is one reason the distinction hasn't disappeared entirely from professional published English even as it has faded substantially from ordinary speech.
Frequently asked questions
Is it 'Who is calling?' or 'Whom is calling'?
Who is calling — 'who' is the subject of 'is calling,' matching 'he is calling,' not 'him is calling.' This is one of the clearest cases: whenever the pronoun is doing the action of the verb, it wants who, never whom.
Is 'whom' considered old-fashioned?
It's increasingly rare in casual speech and can sound stiff there, but it remains standard and expected in formal written English, particularly directly after prepositions (to whom, for whom) and in careful academic or legal prose.
How do I check who vs. whom quickly?
Mentally answer the question or restate the clause using he/she/they or him/her/them. If 'he' fits, use who; if 'him' fits, use whom. Matching the -m ending of whom to the -m ending of him is a handy memory trick.
Is 'whomever' ever correct as a subject?
No — like whom, whomever is always an object form. If the word is functioning as the subject of a verb, even inside an embedded clause, whoever is correct regardless of the larger sentence's structure around it.