All right, it’s time to revisit the ever popular who versus whom discussion.
First of all, I need to say that The Who got it right. In their late 1970′s hit song, the expression “Who Are You” is completely (and always will be) correct. In fact, if they had reversed the expression and said, “You Are Who” it would still be correct.
Some people seem to think that the decision to use who or whom is based on some class structure, some fancy formality. That is, you might say to a stranger at the ball game, “Who are you?” and you might say to a stranger (wearing a tuxedo and thoroughly enjoying listening to a rumble of tubas in the background) at the Governor’s Inaugural Gala Event, “Whom are you.” Well, rest assured, the latter is (and always will be) incorrect.
When the word is the subject, use who. When the word is the object, use whom.
Who is shoveling the snow in front of our house? (Who is the subject.)
I kissed whom? (Whom is the object, receiving the action of the verb.)
You dropped the bratwurst and sauerkraut on whom? (Whom is the object of the preposition.)
Remember, in the case of linking verbs, the noun on either side of the linking verb is to be thought of as the subject.
Who is he? He is who.
If the verb is not a linking verb, though, and if some form of who is being used as the object, then it is the word whom that needs to be used.
You gave the book to whom?
Again, if the form of who is being used as the object of the preposition, use whom.
To whom did you give the book?