For who (or whom?) does that bell toll?
I have seen a lot of mix-ups when it come to the use of who vs. whom. Heck, it is something I usually have to double-check myself whenever I am editing writing. I have read and re-read numerous article online and in grammar handbooks over the years, and still sometimes the question pops up. I will try to break it down for you here to make it easy to remember which who or whom to use when.
A quick, easy tip is that who is always a subject, while whom is always an object. Or, take a look at the sentence and if the who/whom can be replaced with he, then you would use who; if replacing who/whom with him works better, than you use whom.
Who is used as a pronoun, and always the subject of a verb. Sentences that show correct use of who:
It was Sammy who broke all the crayons in the box. (he broke works, not him broke)
Who needs a crayon to use? (he needs a crayon works, not him needs a crayon)
The coach cheered for who tried the hardest. (he tried the hardest works, not him tried)
Whom, while also a pronoun, is used as the object of the verb or preposition. Sentences that show the correct use of whom:
For whom the bell tolls. (it tolls for him, not it tolls for he)
You asked whom to go to the game? (you asked him works, not you asked he)
With whom did you talk? (with him works, not with he)
And if you still have questions after reading this, doing your own Google search and grabbing your closest dictionary, my only other suggestion it to just rewrite the entire sentence completely and avoid the who/whom issue altogether.