German prepositions — which case each one takes

You can know the case tables perfectly and still get every sentence wrong, because in practice the case is usually chosen by a preposition rather than by the grammar of the sentence. Learning the cases without learning which preposition takes which is the most common way to stall.

There are three groups: always accusative, always dative, and the nine that go either way.

Always accusative

Five, and there is a mnemonic that has survived decades of teaching: DOGFU.

Ich gehe durch den Park. — I walk through the park.

Das ist für dich. — That is for you.

They never take anything else. No exceptions to remember.

Always dative

Nine, and worth learning as a chant because they come up constantly.

Ich fahre mit dem Auto. — I go by car.

Ich komme aus der Stadt. — I come from the city.

The nine that go either way

These take accusative for movement into a place and dative for position in a place.

The test is not "is there motion" — it is does the motion cross into the place.

The contractions you will hear constantly

Germans merge preposition and article whenever they can, and in speech the merged form is the normal one.

im and am are dative, ins and ans are accusative — so the contraction itself tells you which one was meant.

Genitive prepositions

A handful take the genitive. They belong to written and formal German, and in speech most people swap in von plus dative.

wegen (because of), trotz (despite), während (during), statt (instead of).

Wegen des Wetters bleiben wir zu Hause. — Because of the weather we are staying home.

Recognise these; you do not need to produce them early.

What to actually memorise

DOGFU, the nine dative ones as a chant, and the crossing-into test for the two-way group. Then learn each new preposition with its case attached, the way you learn a noun with its article — mit dem, für den, and the case stops being a decision you make each time.

The cases themselves are set out in German cases.