In most contexts, the use of who in place of whom is not a serious error. Many English speakers do not routinely use whom in their informal communication, and the word can sound overformal to many listeners even where it is logically correct. Be aware, however, that some people are strict about the who/whom distinction, so if you are writing a school paper or a college application or are applying for a job, using the words in the manner considered proper is safest.
When you’re in doubt, always use who. Most English speakers are used to hearing who where whom would be correct, but the mistaken use of whom where who is the correct form is a more serious blunder.
Who is a nominative pronoun, which is a pronoun that performs an action rather than receives an action. It has two main uses:
- It’s the subject of a verb—e.g., Who gave you that book?
- It’s a predicate nominative (a noun in the predicate that renames or refers to the sentence’s subject)—e.g., This is who I am.
Whom is an objective pronoun, which is a pronoun that receives the action of a verb. It also has two main uses:
- It is the object of a verb—e.g., Whom should I call?
- It is the object of a preposition—e.g., From whom did you get this information?