Dative or not? Hi. My friend who is eine Österreicherin posted a picture on FB of her front room, with posters and stuff on there. I wanted to say to her: Dein Wohlzimmer ist geil! Ich mag die Sachen auf der Mauer. Your front room/living room is cool! I like the stuff on your walls. Now i corrected myself on FB because according to my little grammar chart that i have, auf is a dative preposition and therefore i thought it should be 'den Mauer' but she said that my original der Mauer was correct. So now i'm confused. Can someone explain this and also explain how i would go about picking the right declension of the word Mauer (not even sure i got the correct version of this) in each case? I feel she may be wrong (my chart has always been right) but then who am i to tell a native speaker! Thanks.