Answer: When should you use “who” versus “whom”?

[superhero-specs.livejournal.com]

...with examples from Stargate SG-1 and House

In the Stargate SG-1 Season 4 episode “2010,” Jack O’Neill has the following exchange with Sam’s husband, Joe:

Jack: Did you get it?
Joe: Yes.
Sam: Thank you.
Joe: What are you gonna do with it?
Jack: Send a message.
Joe: To who?
Jack: To whom.

Some Grammatical Background

Who and whom are pronouns. Who is a subject pronoun like I, you, he, she, we, you [all], and they. Whom is an object pronoun like me, you, him, her, you [all], and them.

So,

Who should be used when it is the subject in a clause:

House: Who wants to head over to the prison and find Clarence’s secret stash? (“Acceptance”)

and whom should be used when it is the object of a verb or verbal:

Teal’c: It is he whom we endeavor to locate, O’Neill. (“Crystal Skull”)

or of a preposition:

Gairwyn: [The Asgard] are friend of all, protector of all. Except the Goa’uld, with whom they are at war. (“Thor’s Chariot”)

A Rule of Thumb

You can test which form to use by replacing the who or whom, or answering the question, with the appropriate pronoun:

Daniel: Jack, who are you talking to?
Jack: The woman. (“Abyss”)

The answer to Daniel’s question is that Jack is talking to her, not she, so Daniel should have used whom, not who.

Acceptable "Misuse" in Speech and Writing

In speech, who is commonly “misused” in questions about to whom the addressee is directing a certain action:

Jack: Hey, who you calling a hassick? (“Bloodlines”)

Daniel: Besides, who am I gonna tell? I mean, I don’t, uh, I don’t remember anybody, right? (“Fallen”)

House: Who were you trying to kill in Bolivia? My old housekeeper? (“Whatever It Takes”)

It is of course acceptable to replicate these “mistakes” in your characters’ speech when you’re writing. Just be aware that the construction is in fact grammatically incorrect, and people who speak more formally are likely to use the correct form, whom:

Osiris: Of whom do you speak? (“Summit”)

Speech also makes casual use of who in statements, often as the object of prepositions:

Hammond : If that isn’t O’Neill, I was to know who the hell we’re looking at. (“Cold Lazarus”)

Daniel: Because when this war is over, and every soul that’s left alive is praying to the Ori, feeding their need to be worshipped, you know who they’re going to come for next. (“The Pegasus Project”)

Eve: I’m gonna base this moment on who I am stuck in a room with! It’s what life is, it’s a series of rooms, and who we get stuck in those rooms with adds up to what our lives are. (“One Day”)

Again, this is okay in dialogue, so long as it’s done mindfully. It is NOT acceptable in objective narration. You’ll notice that in all of the above examples, the misuse of who is accompanied by another mistake of putting a preposition (at, for, with) at the end of the clause. To be grammatically correct, a preposition should precede its object. In writing or more formal speech, the correct use of whom is accompanied by the correct placement of the preposition:

Patient: I extracted that you were a person for whom detail is not a major concern. (“One Day”)

House: You ever see an infected pierced scrotum?
Cuddy: Um, no, but I know a few people on whom I’d like to see it happen. (“Heavy”)

Overcorrecting, or When "Who" Isn't Wrong

Be careful not to overcorrect! Just because you see a verb or preposition doesn’t mean that what follows it must be whom. The following uses of who are correct, and you can verify them by replacing them with I, he, she, we, or they:

Daniel: There’s nobody there.
Jack: Look who’s talking. (“Abyss”)

The expanded form of Jack’s comment would be “Look at who is talking.” In this case, the clause “who is talking” is the object of the preposition “at,” but the subject of the verb “is” is “who.” Who is talking? He, not him, is talking.

Daniel: Do you know who the Alterans are? (“Origin”)

Here, the clause “who the Alterans are” is the object of the verb “know,” but within that clause, “who” is the subject of the verb “are.” Who are the Alterans? They, not them, are the Alterans.

Who is also correct if it is used in a restrictive clause to rename the subject of the clause:

Monk: Those who seek one-ness find all that they seek. (“Maternal Instinct”)

Teal’c: A Goa’uld offspring is born with the intellect and knowledge of the queen who bore it. (“Cure”)

Daniel: It is we who must seek the truth of the universe in order to achieve enlightenment. (“Origin”)

Cameron: Kind of hard to work for a guy who doesn’t respect you. (Pilot)

House: I’m the guy who said her C-cups are half-full. (“Needle in a Haystack”)

Note that in the above examples, the who could be restated as the subject of a sentence, and replaced with a subject pronoun:

Who seeks one-ness?
They seek one-ness.

Who bore the offspring?
She bore it.

Who must seek the truth?
We must seek the truth.

Who doesn’t respect you?
He doesn’t respect you.

Who said her C-cups are half-full?
I did.

A Few Last Examples

Stacy: Such a hero. Always righting wrongs. Who cares who you have to manipulate? (“The Mistake”)

Here, the first who is correct: Who cares? She cares.
But the second who is wrong: Whom do you have to manipulate? You have to manipulate them.

House: Hi, I’m the guy who saved your life. (“Mirror Mirror”)

House: Get to the truth about who he’s been dating. (“Top Secret”)

In the first quotation, who is correct: Who saved your life? I did.
But the second who is wrong: Whom has he been dating? He’s been dating her.

Wilson : Cameron’s got [the patient] on dialysis and he’s stable for the moment, unlike Cuddy, who’s suicidal. (“Failure to Communicate”)

Here, the clause "who's suicidal" can be restated as its own sentence, with who as the subject: Who is suicidal? She is suicidal.

Daniel: I dunno, it depends on who you ask. I thought I had a certain je ne sais quois. (“Grace”)

This use of who is incorrect, not because “who you ask” is the object of the preposition “on,” but because “who” is the object of “ask”: Whom do you ask? You ask him.

So, Where Does This Leave Us?

The usage of who and whom is currently debated by linguists, largely because as whom becomes less and less common, it seems more and more unfair to call who a mistake in places where whom just sounds too awkward. If you’re interested in this debate, you can find several articles ranging from silly to scholarly at Language Log.

My advice is this: Remember that who is a subject pronoun and whom is an object pronoun, and the choice between them should be based on the word’s grammatical role in the clause in which it appears. If you’re not sure which to use, try replacing who or whom with another pronoun. If it’s a subject pronoun, use who; if it’s an object pronoun, use whom. If you’re using the word in casual dialogue, or whom just sounds too awkward, err on the side of misusing who, as the overuse of whom will make your writing sound not just pompous but foolish.

So to Jack I'd say, you’re right. The grammatically correct question would be, “To whom are you going to send a message?” But nobody really talks like that unless he’s a power-hungry egomaniac bent on galactic domination, so give the poor guy a break.

Sources:
Dictionary.com
WikiQuote.org
Language Log