Or is it whom? In what context would I either use whom or who? Does it have to do with placement in the sentence? Also, whose and who is? I believe whose is used as a possessive article... I'm not too sure though. (Who's sitting in my chair?, Whose car is sitting on my lawn?)
Who is correct; whom is not. "Who" is the subject of the verb "will". You could rephrase the question as "This post will be answered by whom?" In that case, "post" is the subject. At least, I think that's how it works. By whom are other ideas had?
Correct. Who is the subject of the sentence. Whom takes the role of the acute case or objective case in English. Hence, by whom, for whom, to whom, from whom, etc. A preposition is your indicator, your flag, that what follows is no longer the subject of the sentence. EDIT ~ For the most part. There are constructions in English which are a little more convoluted that will not strictly adhere to this rule.
Who will reply to this post? He will reply to this post. Will he reply to this post? Who = He To whom are your referring? Are you refererring to him? With whom will you go? I will go with him. Whom = him I am not saying this is correct but just lately I have been trying to get my head around who and whom and this is how I have interpreted the rules.
Ok, thanks guys! It makes much more sense know that I've heard it... Who - the primary subject: Who is in the kitchen? Whom - the secondary subject: The bed is occupied by whom? Score!
Note that modern usage accepts who in nearly every context in which whom is technically correct. About the only case that will even raise an eyebrow is if you use who as the object of an adjacent preposition. For example, if you say: To who was the letter addressed? just about any editor would correct it to: To whom was the letter addressed? But if you rearrange it to: Who was the letter addressed to? most editors would leave it alone, even though it parses exactly the same.