"Whom" is used in any case where you'd use an object pronoun, such as "me" or "him" or "them". Do you ever say "for I" or "for he" or "for they"? No, you say "for me" or "for him" or "for them", so you'd say "for whom", and since it doesn't matter which "whom" it is, it is "for whomever".
Not so!
"Whom" is used in certain old expressions, such as "for whom the bell tolls," and in situations where you want to make a statement with your word choice. Otherwise people say "who." "Whom" is dying.
I don't
quite agree—
whom is pretty robust with pied-piped prepositions, as in
To whom should I direct this request? Admittedly, pied-piping prepositions is itself pretty rare—people would mostly just say
Who should I direct this request to?, with the preposition stranded at the end of the sentence—but it's far from obsolete. (It's certainly less obsolete than
whom is in non–pied-piping contexts, for instance.) And as far as I can tell you almost always get
whom and almost never
who in that situation.
(Also, maybe this should be moved to another thread.)
