Quote Originally Posted by mashamania
Quote Originally Posted by ReDSanchous
I've always thought that who and whom are interchangeable. seems like whom is kind of formal. I hardly ever use it.
Who, whoever, etc are nominative. Whom, whomever, etc are non-nominative. So its "Whoever called me STFU!" lol, but its "Call whomever you want" or "To whom it may concern" but not "To who it may concern."

But whom is becoming archaic, especially in casual conversation. In most cases you can use who in place of whom and it actually sounds more normal.
Thanks for the explanation!
Well, in the phrase 'To whom it may concern" whom is used because there's a preposition. If I remember correctly, 'who' cannot be used if there's a prepostion in a sentence. For instance, you cannot say: I saw the guy to who you spoke yesterday. You should say: I saw the guy who you spoke to yesterday OR I saw the guy to whom you spoke yesterday.
Perhaps, I'm wrong because it was a very long time ago that I last saw the rule explaining the difference between 'who' and 'whom'.