I am writing a book, and I ended up throwing in a discussion of "Who vs. Whom" because I realize that most of the time, I get it right but occasionally I get it wrong. So I decided to look it up. I ended up adding an entry in Wiktionary (the dictionary companion to Wikipedia) for who and the variations (who, whom, whoever, whomever), because I looked it up to figure out exactly what the rule is. Here's what I added:
Whom is an object pronoun, while who is a subject pronoun. One would never use whom as the subject of a verb. One method to use to determine correctness of who vs. whom is to rewrite the sentence to eliminate who or whom. If you would have used he, she, or they, in place of the word, then who is the correct word; if you would have used him, her, or them, then whom is the correct word.
This also applies for whoever and whomever, in which if you would replace the word with 'he' or 'she', then 'who' or 'whoever' is the correct word; if you would use 'him' or 'her' instead, then 'whom' or 'whomever' is correct.
In the famous Mamas & The Papas song Go where you wanna go there is a line, You gotta go where you wanna go, Do what you wanna do With whomever you want to do it, babe. We can rephrase the end of this sentence correctly as "with him or her, babe". We cannot correctly rephrase the sentence as "with he or she, babe" and thus, "whomever" was the correct word in the line of that song.
As it turns out, I have this conversation on (what is currently) page 584 of my book "In the Matter of: Instrument of God"
"How many women were there back at the house?"
"Who was the other one?"
"Lynn. I believe that question should have been phrased, ?whom'."
"Uh, no, in this case it is correct. I remember this one from my English class. If you try to replace "who" or "whom" in the sentence, and if you would have used ''he'', ''she'', or ''they'', then ''who'' is the correct word; if you would have used ''him'', ''her'', or ''them'', then ''whom'' is correct. I can rephrase the question as a sentence of the form ?she was the other one.' I can't rephrase it to use ?her' or ?them,' and therefore ?who' is the correct word. How is that?"
"Gee, thanks, I always have trouble with that one."
"So did I until I learned, but, again, I didn't write the questions, I just read them."
Later, on page 596 I had written a line using the word 'whom' and realized, now that I know the rule, I'd made a mistake, so I get to revisit the idea.
"George even told me, anytime I want someone killed just let them know and they'll be on their way to my Department within 24 hours."
"Whom is he using, CIA, KGB or Mossad?"
"Hey! You used the wrong word there."
"What do you mean?"
"The last place I was at, I got into a discussion with someone over ?who vs. whom'. You're using it wrong. If you can use ?he' ?she' or ?they' in place of the word, you use ?who' and if you would use ?him', ?her' or ?them', you use ?whom'."
"Uh, yeah, you're right, I could say, ?He is using' instead of ?whom is he using' so I should have said ?who'. I usually just remember the ?m' rule. If you could say ?him' or ?them'," he says, emphasizing the ?m', "then you use ?whom', if you'd use ?he' or ?they', then you use ?who'."
"Hmm, yeah, that's even easier to remember."
"Well, anyway, who is he using, CIA, KGB or Mossad?"
So anyway, now I have helped make the world's English maybe just a little more correct.