I’m sure this has been answered before, but I can’t find it. A quick search yielded an explanation only a pHD could understand. Any concise explanation for which to use in a given context?
Thanks
Who did you arrive with?
With whom did you arrive?
I don’t know the proper answer, but I assume the ‘contexts’ are the different sentence structures.
I = Who
Me = Whom
If the statement is “I have the next birthday” then the question is “Who has the next birthday?”; “I have” = “Who has”.
If the statement is “Give the presents to me” then the question is “To whom do I give the presents?”; “To me” = “To whom”.
Note that “Whom do I give the presents to?” is grammatically incorrect but more commonly used.
“Whom did you arrive with?” and “Whom do I give the presents to?” are both grammatically correct. A little formal, and you can get away with “who” in either case, in anything except formal writing. And if it’s that formal, you might want to put the preposition up front, because it sounds a little more clear.
The one place when I hear people use “whom” when “who” is correct, is always the “whomever” form. People say “I’ll go with whomever will take me,” but this is incorrect. In this case, the object of the preposition “with” is not “whomever,” but is the whole phrase “whoever takes me” (the correct form), and “whoever” is the subject of this clause, so gets the subjective form.
Actually, the most commonly used is “Who do I give the presents to?” And this is OK colloquially. “Who” is the subjective (nominative) case and “whom” is the objective case, but colloquially hardly anyone uses “whom” anymore. But whom cares? 
Similar to what boofy_bloke suggests, I learned that he/him corresponds to who/whom.
In actual practice, it seems that “whom” is dying out. A hundred years from now it’s likely to be archaic.
Who=subject
Whom=direct object and indirect object
A direct object (accusitive case) is whatever the verb of the sentance is being performed on. An indirect object (dative case) is to or for whom the action is being performed. E.g. Billy gave flowers to Suzy. Billy is the subject (nominative case), flowers is the DO (accusitive case), and Suzy is the IO (dative case). When in doubt ask, “Billy gave what?” The answer is the DO. “Billy gave flowers to or for whom?” The answer is the IO.
Ekk! “Whom did you arrive with?” is definitely NOT correct! It would be “With whom did you arrive?” It may not be how we speak, but it’s correct. (And yes I know I wrote a sentance myself that ends with a preposition, even though I know it to be incorrect). The whom part is right though. 
Sorry, should have cleared this one up in the OP. Part of the problem is I never paid attention to ‘dative’ ‘accusative’ ‘nominative’ , etc. This was also the reason I hit a roadblock in my German grades 2nd year of college.
Probably no help for me on this, but some of the suggestions at least give me a glimmer of hope to find an answer I can understand.
Thanks for the effort though, I appreciate it.
=http://www.dummies.com/WileyCDA/DummiesArticle/id-1181.html]This is the easiest explanation I could find.
Does the use of “whom” add anything to the language, in the sense that it clears up otherwise ambiguous sentences?
Here is what the American Heritage dictionary says about usage of who/whom:
This is something up with which I shall not put.
The idea that it is grammatically incorrect to end an English sentence with a proposition is as archaic as the idea that a split infinitive is wrong. Both come from imposing Latin grammer on English.
And I agree that whom is on its way out. You gave me a present. I gave you a present. No confusion. Whom really adds no infornation. But I still get a kick out of people who use “whom” in the subject of a sentence instead of “who”, thinking they sound more educumated.
Ha, that Usage Note is at around a 20th grade reading level.
John Mace – You’re correct, but it is extremely rare for someone to end a sentence with a preposition, and it’s usually incorrect when the do so.
What people **do[/] end sentences with are particles of verbs. The fact that most particles are also prepositions confuses a lot of people.
To clarify:
To put = to place
To put up = to can (as in canning preserves)
To put up with = to tolerate
Leaving off the particle changes the meaning. If you say “This is something I won’t put up with,” the last two words are part of the verb and you’re not ending with a preposition.
And not ending a sentence with a preposition can get you into big trouble. Joceyn Elders, when asked about masturbation, remembered the rule and said, “That is something that should be taught” (implying there be lessons in the practice) when she clearly meant, “That is something that should be taught about” (implying people be told it existed). She lost her job as Surgeon General as a result.
Back to “whom,” there is one essential reason (originally voiced by Merv Griffin): When challenged to find a sentence where you were required to use whom, Griffin said, “Whom on the range.”
I knew this was setting myself for failure. Like I said, I don’t know beans from nominative,dative, etc. Do you honestly think I know past participles, dipthongs, etc?
I have never claimed to be an English Major, I just wanted to know who/whom usages. If they’re going out of style, I won’t worry about it. I’ll just ride the storm out.
When I write/speak, I’ve never been ridiculed, so I assume it’s archaic already. In addition, I hold fast and true to “American” English. I hold that the American version of English is/ will be the internationally held dialect. Any discussion on this is welcome. Any flames of “American” English, please start a new BBQ thread
Well, there’s the story of the convicted prostitute up for parole who tried to end her sentence with a proposition, but that’s quite a different circumstance.
In point of fact, we’re playing Pedantic Prescriptivist in claiming “It’s incorrect to end a sentence with a preposition,” but not in defending whom.
The usage is quite simple: Spoken English, except in the speech of the greatest precisionists, sees nothing wrong in a terminal preposition, and in a who used objectively but disjunctively. “Who are you coming with?” is quite correct spoken English, but most literate speakers would say “Send that letter to Corporate HQ, addressed to whom it ought to be sent…” instead of “…to who…”
In most written English, friendly letters to one side, moving the preposition to the beginning of the sentence and following it with whom is still customary – but less out of obedience to a debatable rule than that the sentence is usually clearer written in that form, especially if it is relatively long. “Okay, you want 2001 sent to all Science Fiction Book Club members. Who did you want to send 2010: Odyssey II to, too?” Extreme example, but switch that one around!
Real simple answer to the OP: Imagine that the answer to the question calling for "who or “whom” is “he” or “him” – use “who” whenever you’d use “he” to repeat the sentence as an answer; use “whom” when you’d use “him.”
But, of course, on Abbott and Constello’s baseball team, they put Who out at second on a fielder’s choice play.
Oh, but you do. If you know the difference between “he” and “him”, you already know the difference between “who” and “whom”.
This is the third time I’ve seen this claimed, so I want to be sure it gets pointed out clearly that ClairaJade and the other two are absolutely, positively wrong about this. “Whom did you arrive with?” is completely correct, althout it’s acceptable to use “who” in informal settings. In formal settings, it’s preferred to put the preposition up front, but whether it’s in the front or the end, “whom” is its object, therefore takes the objective case.
What RealityChuck is saying is that there are two ways of looking at how a sentence would get diagrammed in these cases.
Take the question “Whom did you arrive with?” The older-fashioned way is to say that “you” is the subject, “did arrive” is the verb, an intransitive one (which doesn’t take an object), and “with whom” is a tacked-on prepositional phrase. In this case, the question ends in a preposition (nothing wrong with that, of course).
A more modern view is that “you” is the subject, but we’ve turned the verb from intransitive to transitive (needs an object to receive the action) by tacking on this other part, which by itself would be a preposition. In this view, “did arrive with” is the verb, and “whom” is the object of that verb. This makes sense to native speakers, but was never taught in schools back in my day.