Who vs Whom

Use who when asking about or referring to the subject of a sentence or clause—that is, the person doing the action.

Use whom when asking about or referring to the object of a verb or preposition—that is, the person receiving the action or related to a preposition.

To decide between who and whom, try replacing the word with he/she (for who) or him/her (for whom); if he/she fits, use who, if him/her fits, use whom.

Use whom after prepositions when the question or relative clause requires an object, though in informal speech who often appears instead.

In questions, use who for the subject position and whom for the object position to keep the sentence clear and grammatically correct.

In relative clauses, use who for subjects and whom for objects of verbs or prepositions; sometimes whom can be omitted in informal contexts.

Remember that who asks for or replaces the subject and whom asks for or replaces the object; use the quick test to guide you and pay attention to prepositions.