Who versus Whom?

Question

Can someone please explain to me when it is appropiate to use one instead of the other.

Answer 1

"If you can’t get who and whom straight, try this trick: rephrase the sentence to get rid of who or whom. If you find you’ve replaced who/whom with he, she, or they, who is correct. If you find you’ve replaced who/whom with him, her, or them, then whom is correct. "

Answer 2

MissMary's techniue is really good, if you know how to use him/he, her/she, and them/they correctly. The more technical answer is that "who" is a subject, and "whom" is an object. So, if you have a direct object, indirect object, or object of a preposition, use the word "whom." If you are using the word as the subject of the sentence, then use "who."

We should say, "to whom," "for whom," "with whom," etc.
We should say, "who is," "who will," "who can," "who did," etc.