Who vs Whom

Many English speakers do not know the difference between who and whom. In some places, it hardly 

matters, because using who when you should use whom is so common that it's not even considered much 

of a mistake. But for those who want to know the difference between who andwhom, here is an 

explanation.

To put it simply, “who” is a subject and “whom” is an object.  A classic mneumonic device to remember this, courtesy of Grammar Girl, is “I love you.”  In this sentence, “I” is the subject – who is performing the action of the sentence. “I” am doing the loving.   “You” are the object of my affection, as well as the object of the verb.  ”You” are receiving the love.  Therefore, I = who, you = whom.

If we turn this into questions, it would be:

• Who loves you? (You are asking about the subject.)
• Whom do you love?  (You are asking about the object of the action.)

When choosing between who and whom, ask yourself: are you talking about the subject of a sentence (who), or the object of the action in the sentence (whom)?

Some examples:

Wonder Woman, who just celebrated her 600th issue, underwent a drastic costume change. (We use “who” because it refers to the subject, Wonder Woman.)

Who is responsible for this new look?

Wonder Woman did not know whom to save first:  Superman or Batman. (We use “whom” because it is the object of the verb “know.”  Wonder Woman is performing the action and whom is the one receiving the action.)

The Trinity

Last trick to remember the difference:  he = who and him = whom.  Notice how him and whom both end in m?  When trying to choose between who or whom, ask yourself if the answer would be he or him.

• If the answer is he (or she), then use who.  Who is the only superhero that can rival Wonder Woman’s power?
  • He (Superman) is the only superhero who can rival Wonder Woman’s power.
• If the answer is him (or her), then use whom.  Who fell under Max Payne’s malevolent telepathic control?
  • Max Payne seized telepathic control of him (Superman), whom Wonder Woman rescued.

Who has still has questions?  :)
Taken from: http://englishteachergeek.wordpress.com