Tell it apart
| Aspect | Who | Whom |
|---|---|---|
| Job in the sentence | Subject: does the action | Object: receives the action |
| Pairs with | he, she, they | him, her, them |
| Example | 'Who called you?' | 'To whom should I address this?' |
| Register | Every style, including formal | Formal; rare in speech |
Who does the action; whom receives it. That's the rule in formal English, and it matters most after a preposition ('to whom', 'with whom', 'many of whom'). In everyday speech and most informal writing, who has largely taken over both jobs, and 'Who did you invite?' is normal, natural English rather than a mistake.
What it really means
Who and whom are the same word in two different jobs. Who is the subject, the one doing something: "Who broke the vase?" Whom is the object, the one something is done to: "Whom did the dog bite?" It's the same split you already make without thinking in he/him, she/her and they/them.
The difference is real, but it has faded. Whom is now mostly a formal word. It feels at home in writing, after a preposition ("the colleague with whom I share an office") and in phrases like "many of whom". In conversation, "Who did you speak to?" is what nearly everyone says, and dictionaries for learners of English present it as the natural choice.
So the practical advice is two-sided. In a formal letter, an essay or a legal document, use whom for objects, especially straight after a preposition. In a text or an email to a friend, who is fine. The mistake worth avoiding is the overcorrection: reaching for whom because it sounds grand, in a spot where the subject form belongs ("Whom shall I say is calling?").
Memory trick. Answer the question in your head with he or him. If the answer is him, the word gets an m too: whom. "Who/whom did you invite? I invited him", so formally it's whom. "Who/whom is at the door? He is", so it's who.
In real life
- Right: Who left the window open? (who is the subject: someone left it open)
- Right (formal): The candidate whom the panel chose starts on Monday. (the panel chose her)
- Wrong: Whom is coming to dinner? (the person is doing the coming, so it's who)
Questions
Q01What is the difference between who and whom?
Who is a subject pronoun, like he or they: 'Who wrote this?' Whom is an object pronoun, like him or them: 'Whom did you see?' Whom is formal; in speech most people use who for both.
Q02Is it 'to who' or 'to whom'?
Directly after a preposition, formal English uses whom: 'to whom', 'for whom', 'with whom'. If you move the preposition to the end, who is usual: 'Who should I write to?'
Q03Is using who instead of whom wrong?
Not in ordinary English. Learner's dictionaries note that whom is not used very often in spoken English and that who is the usual object pronoun in questions. Using whom where who belongs ('Whom is calling?') is the error that actually stands out.
Sources
- Who, whom — Cambridge Dictionary, English Grammar Today.
- whom (pronoun), with grammar point — Oxford Learner's Dictionaries.
- who (pronoun) — Oxford Learner's Dictionaries.