Is it
Who are you talking to?
or
Whom are you talking to?
:dubious:
I learned in school that if you rearrange the sentence to something like “Are you talking to him/her/he/she” you’ll have your answer, as him/her = whom, and he/she = who. Thus, “To whom are you talking?” would be the correct wording, though we rarely speak that way. It’s more like you’ll hear/ask, Who are you talking to?
Does that make sense?
Whom, as in “to whom are you talking”. It just sounds weird to say “whom” at the start of a sentence.
In informal English (i.e., the kind of English that especially ignorant prescriptivists think is inherently wrong), “whom” does not exist and prepositions can be left at the end of the sentence. So it would be “Who are you talking to?”.
In the kind of English where you follow superstitious rules that especially ignorant prescriptivists think are inherently correct, “whom” is used for objects of verbs and prepositions, and prepositions cannot be left at the end of the sentence. So it would be “To whom are you talking?”.
The two other logical options of course are “Whom are you talking to?” and “To who are you talking” (that last one sounds especially weird), which mix the two kinds of English. To the extent that the ban on preposition stranding is even more stilted than the use of “whom”, I think “Whom are you talking to?” is viable. The problem with “To who are you talking?” is that the fronted preposition sounds extremely stilted and anyone going to such things to sound stilted would also probably be using “whom”.
If it sounds weird to say “whom” at the start of a sentence, then you’re going to be in trouble when “whom” is the object of a verb: “Whom did you see?” In that case, there is no preposition to go along for the ride.
(In case you want a more theoretical answer: Let’s imagine a variant of Prescriptively Correct English where “whom” exists but preposition stranding is fully okay. In such a variant, would it be “Whom are you talking to” or “Who are you talking to?”. My guess is that it would be “Whom are you talking to?”. Based on what I know about (the linguistic literature on) languages with richer case morphology, case assignment is not sensitive to surface word order, it’s sensitive to underlying logical dependencies. The fact that “whom” is the logical object of “to” means that it should be “whom”, regardless of where it appears in the sentence.)
“To whom art thou talking to.” If you’re going to drag out nearly obsolete grammer why half-ass it?
“Sounds weird” is the true criterion of incorrect grammar. (Well, that and “means something else”.)
I fully agree. I think I’ll be stealing this in the future.
No, I think it’s better to say, “Which man talk’st thou to?”
Yeah, but you’d be wrong.
It would be “whom.” The use of prepositions at the end of sentences predates the loss of “whom.”
In modern* English, “whom” should most often be avoided.
*Note, I didn’t capitalize that word.
You’ve double "to"ed.
Wrong in what way?
Dang it! I mean, yes, quite right. Congratulations on being the only one to pass my totally intentional test. Well done.
Aesthetically, of course. I’m egotistical enough to act as if my personal preferences are objective universal truths.
Sounds weird to whom? 
At least you said criterion instead of criteria.
Me.
Weren’t you paying attention?
I was about to say, we just did this question. I didn’t realize it was the same OP. What the heck?
The suggestion
[QUOTE=Giles]
“Which man talk’st thou to?”
[/quote]
has been characterized as wrong, but the response to Indistinguishable’s question (as to why) seems lacking. Apropos is the memorable retort of a character created by an esteemed professor of English/philology:
[QUOTE=Eowyn, from ROTK]
I am no man!
[/quote]