Most German prepositions always take the same case. But nine of them can take two, and they cause more confusion than almost anything else at beginner level. The good news is that one question decides which case you need.

The one question

These nine prepositions are an, auf, hinter, in, neben, über, unter, vor and zwischen. After them, ask:

  • Wo? (where?) means a position or a place, so use the dative.
  • Wohin? (where to?) means movement towards a place, so use the accusative.

Ich bin in der Küche.

I am in the kitchen. (Wo? Dative.)

Ich gehe in die Küche.

I am going into the kitchen. (Wohin? Accusative.)

It is the same preposition, in, in both sentences. Only the case, and so the article, changes. Compare the definite articles:

  • Masculine: auf dem Tisch (wo?) and auf den Tisch (wohin?)
  • Feminine: in der Küche (wo?) and in die Küche (wohin?)
  • Neuter: an dem Fenster (wo?) and an das Fenster (wohin?)

Only one letter separates dem from den, so masculine nouns are where most mistakes happen. Note that in dem usually becomes im, in das becomes ins, an dem becomes am and an das becomes ans.

Let the verb help

Many verbs come in pairs, and the pair tells you the case. A verb that describes where something is goes with the dative, and a verb that describes putting something somewhere goes with the accusative:

Das Buch liegt auf dem Tisch.

The book is lying on the table.

Ich lege das Buch auf den Tisch.

I put the book on the table.

The pairs to learn are stehen / stellen (to stand / to stand something), liegen / legen (to lie / to lay), sitzen / setzen (to sit / to seat) and hängen / hängen (to hang, which has two versions of its own: das Bild hängt an der Wand but ich hänge das Bild an die Wand).

A catch: moving around inside a place

If something moves but stays inside the place, the question is still wo?, so use the dative.

Die Kinder spielen im Garten.

The children are playing in the garden.

Die Kinder laufen in den Garten.

The children are running into the garden.

In the first sentence the garden is where they are. In the second it is where they are heading.

A second catch: fixed combinations

Some verbs come with their own preposition and their own case, whether or not anything moves. These do not follow the wo and wohin test, so learn them with the verb:

Ich warte auf den Bus.

I am waiting for the bus.

Ich denke an dich.

I am thinking of you.

Both use the accusative, although nobody is going anywhere.