Prepositions determine the case of the accompanying nouns or pronouns. There are two main categories :


One-case prepositions.


Most prepositions govern only one case.


ohne + accusative ohne seine Hilfe
nach + dative nach der Pause
infolge + genitive infolge dichten Nebels


This category also includes prepositions that, in everyday language or dialects, can govern two (or even three cases), without any changes in their meaning


wegen + genitive / (dative) wegen Umbaus / wegen Umbau
ab + dative / (accusative) ab 18 Jahren / ab 18 Jahre
entlang + accusative / dative / genitive den Fluss entlang / entlang dem Fluss / entlang des Flusses



Two-case prepositions

This category includes prepositions that can govern two cases. The change of case changes the meaning of the preposition.


Examples   meaning
in + accusative Tu die Milch in den Kühlschrank! direction
dative Die Milch ist im Kühlschrank. state/absence of motion
an + accusative Paul hängt das Bild an die Wand. direction
dative Das Bild hängt an der Wand. state/absence of motion