"Who" is the subject (does the action); "whom" is the object (receives the action).
Subject pronoun: replaces "he", "she", or "they" in a clause.
Who called me while I was in the meeting?
The woman who lives next door is a doctor.
Who is going to present the project tomorrow?
Object pronoun: replaces "him", "her", or "them" in a clause.
To whom should I address this letter?
The candidate whom the committee selected has ten years of experience.
With whom did she travel to the conference?
Common mistake
Using "who" where "whom" is grammatically required: "who did you call?" is very common but should be "whom did you call?" (you called him/her, not he/she). In informal spoken English, "who" is increasingly accepted in object position. "Whom" is required in formal written English and after prepositions: "to whom", "for whom", "with whom".
Trick to remember it
Substitution test: answer the question using "he/she" or "him/her". If the answer uses "he" or "she" — who. If it uses "him" or "her" — whom. Example: "who/whom did you call?" — "I called him" (not "I called he") — whom. "Who/whom called you?" — "he called me" (not "him called me") — who.
Quick rule
Who = subject (does the action, like he/she). Whom = object (receives the action, like him/her). After a preposition (to, for, with, by): always whom.
Did you know?
"Whom" is going extinct in spoken English. Linguists predict that in a few generations it will disappear from everyday speech and remain only in formal or legal texts, as already happened with "thee" and "thou". For now, using it correctly signals high-level written English.
Exercise 1 · Pick the right one
_____ did the manager promote to the senior position?
Exercise 2 · Pick the right one
_____ left these boxes in the hallway? We need to move them.
Exercise 3 · Form the word
Who = subject (does the action, like he/she). Whom = object (receives the action, like him/her). After a preposition (to, for, with, by): always whom.
Using "who" where "whom" is grammatically required: "who did you call?" is very common but should be "whom did you call?" (you called him/her, not he/she). In informal spoken English, "who" is increasingly accepted in object position. "Whom" is required in formal written English and after prepositions: "to whom", "for whom", "with whom".
Substitution test: answer the question using "he/she" or "him/her". If the answer uses "he" or "she" — who. If it uses "him" or "her" — whom. Example: "who/whom did you call?" — "I called him" (not "I called he") — whom. "Who/whom called you?" — "he called me" (not "him called me") — who.
Bryan López
Founder of SpeakUP Academy