Who refers to someone performing the action of a verb (e.g. "They are the ones who sent me the gift"), and whom refers to someone receiving the action of a verb ("I'd like to thank the gift-givers, whom I've known for years"). In grammar terms, that makes who a subject, and whom an object.
We use whom to refer to people in formal styles or in writing, when the person is the object of the verb. We don’t use it very often and we use it more commonly in writing than in speaking.
“Whom” is also used after prepositions, such as in phrases like “to whom,” “with whom,” and “for whom.” Correct use of these pronouns demonstrates a strong command of English and is crucial for clear communication, especially in formal contexts like business meetings or exams.
Use this they/them method to decide whether who or whom is correct.
If who/whom is an object (the one receiving the action), use whom. Let’s look at our first example: Think about who you want to cover and who is eligible for coverage.
Who or Whom? Get It Right Every Time with These 3 Tricks
Who is the subject of a sentence or clause (who is performing the action), whereas whom is the object of a verb or preposition (whom is affected by the action).
Who, whoever, whom, and whomever are pronouns— words that take the place of a noun in a sentence. The difference between who and whom is what part of the sentence they replace.
Language evolves over time, and “whom” is quite rare in modern usage. If you say “Who should I talk to?” instead of “Whom should I talk to?”—most people won’t notice.