auf dem Tisch vs. auf den Tisch
Could someone enlighten me as to when to use which? Thank you!
It depends on whether it's taking the accusative or dative. Since 'auf' is a two-way preposition, it will generally take the dative when describing the position or location of something (indirect object), but the accusative otherwise, such as describing an action. (direct object)
Es ist auf dem Tisch. (dative, "It's on the table.") Er legt es auf den Tisch. (accusative, "He's laying it on the table.")
More humorously, if I recall correctly: Ich warte auf den Arzt. (I'm waiting for the doctor.) Ich warte auf dem Arzt. (I'm waiting on top of the doctor.)
Accusative is the direct object, and dative is the indirect object, generally. In 'He gives that to me.', 'He' is nominative, 'that' is accusative, and 'me' is dative. I think English doesn't usually distinguish accusative and dative as visibly, but we do share the concept of direct and indirect objects.
It's a little hard to put into words, but for the two-way prepositions (an/auf/hinter/in/neben/über/unter/vor/zwischen), if the preposition describes the action, it takes the accusative. If it describes the existing position or location of something, it's dative.
'He sits (down) in the chair' is 'Er setzt sich auf den Stuhl'. (if I'm remembering correctly) 'He is (currently) sitting in the chair' is 'Er sitzt auf dem Stuhl. In the former, the action is the man sitting himself down in the chair, so 'auf' takes the accusative. The latter is only describing that the man is already sitting in the chair, (in a simple sense, 'nothing is moving'), so it takes the dative.
Here's an article which does a more thorough job of explaining two-way prepositions: http://german.about.com/library/weekly/aa052101a.htm
Haha! Your last example was pretty funny!
Unfortunately, I'm still a little unclear. As judysavit mentioned, I'm not familiar with the difference between "dative" and "accusative".
So when you say "Es ist auf dem Tisch," the "dem" describes the "it"? And when you say "Er stellen die Teller auf den Tisch," you're describing, erm, "placing of plates"?
Gets rather confusing for me. :(
We are all confused. Here is the best source I have found online: http://www.german-grammar.de/grammar/content/english_german_table_of_content.htm
Everything is there.
It really does come down to - is the indirect object receiving an object (this usually requires an action verb).
"The plate is on the table"
verb : is
subject : plate
indirect object: table
is the table receiving an object? no = dative
"He puts the plate on the table"
verb : puts
subject : he
object : plate
indirect object : table
is the table receiving an object? yes = accusative
Ever wonder why "mit" is always dative? Because if an object is with something it impossible to be receiving the object when it is already with the indirect object.