Some prepositions require the dative case....do all? Or, do some dictate another case, and if so how does one find which requires which case? How about "für" does it affect case at all?
Prepositions require either the dative case, the accusative case or (less common) the genitive case. "Für", for instance, requires the accusative case. A good dictionary will tell you which case is needed when you look up the preposition.
Most prepositions like "für" can be followed by only one case. However, a certain group of prepositions called "two-way prepositions" can be followed by either the dative case or the accusative case depending on whether they indicate a fixed location (dative) or motion (accusative).
Ex. 1 "Ich bin in EINEM Haus" (I am in a house. Fixed location - dative).
Ex. 2 "Ich gehe in EIN Haus" (I go into a house. Movement - accusative).
Dative prepositions: aus, außer, bei, mit, nach, seit, von, zu, gegenüber
Accusative prepositions: durch, um, gegen, für, bis, ohne, entlang [when used as an accusative preposition, "entlang" comes after the noun, e.g. "die Straße entlang" = along the road]
Genitive prepositions: anstatt, statt, außerhalb, innerhalb, trotz, während, wegen
Two-way prepositions: vor, hinter, über, unter, neben, an, zwischen, auf, in