What are the nine two-way prepositions?

An, auf, hinter, in, neben, über, unter, vor, zwischen. All nine take the accusative for movement towards a place and the dative for position. The test is wohin? for where to, against wo? for where at.

Is there a trick for the dative verbs?

Not a rule, but the list is short enough to learn: helfen, danken, folgen, gehören, gefallen, passen, schmecken, antworten, glauben, gratulieren, begegnen. Many involve doing something for or to a person rather than acting on an object, which is a weak pattern but a memorable one.

Why does only the masculine change in the accusative?

Historical erosion, the other genders lost the distinction over time. It has a practical consequence worth knowing: you can produce a lot of correct German while ignoring the accusative entirely, right up until a masculine noun appears. That is why the case feels sporadic rather than systematic at first.

Which one to useA2

Akkusativ vs Dativ

The short answer

The accusative marks the direct object: the thing being acted on. The dative marks the indirect object, usually the person receiving something. Three things decide which you need: the verb, the preposition, and with two-way prepositions, whether there is movement towards a place.

At a glance

Akkusativ or Dativ?

Compare	AkkusativThe direct object. What is acted on.	DativThe indirect object. Who receives.
The question it answers	Wen? Was?	Wem?
Masculine article	den / einen	dem / einem
Feminine, neuter, plural	die, das, die	der, dem, den (+n on the noun)
Fixed prepositions	durch, für, gegen, ohne, um	aus, bei, mit, nach, seit, von, zu
Two-way prepositions	Movement towards: in die Stadt	Position: in der Stadt
Typical verbs	haben, sehen, kaufen, brauchen	helfen, danken, gehören, gefallen, antworten

How to choose

Ask these, in order

1
Is there a preposition, and is it on a fixed list?
The preposition decides outright. Durch, für, gegen, ohne, um always take the accusative; aus, bei, mit, nach, seit, von, zu always take the dative.
Ich fahre mit dem Bus durch die Stadt.
I’m going through the city by bus.
NBMit forces dative, durch forces accusative, in the same sentence.
2
Is it one of the nine two-way prepositions?
Ask whether there is movement towards a destination. Movement takes the accusative, position takes the dative.
Ich gehe in die Küche. / Ich bin in der Küche.
I’m going into the kitchen. / I’m in the kitchen.
3
Is the verb one that always takes the dative?
Dative, regardless of what the object looks like. Helfen, danken, folgen, gehören, gefallen, passen, antworten, glauben.
Kannst du mir helfen?
Can you help me?
NBEnglish “help me” looks direct; German helfen never is.
4
Are there two objects?
The person takes the dative, the thing takes the accusative.
Ich gebe meinem Bruder das Buch.
I’m giving my brother the book.

Side by side

Each one, in full

Akkusativ

When to use the accusative

The direct object. What is acted on.

The accusative marks whatever the verb acts on directly: ich sehe den Mann, wir kaufen einen Tisch. Only the masculine changes visibly: der becomes den, ein becomes einen, which is why the case is easy to overlook until a masculine noun appears.

It follows five prepositions unconditionally: durch, für, gegen, ohne, um. And with the two-way prepositions it signals movement towards a destination, which is the distinction most worth practicing.

Ich habe einen Termin um drei.

I have an appointment at three.

Sie hat das Fenster geöffnet.

She opened the window.

Wir laufen ohne den Hund.

We’re walking without the dog.

NBOhne always takes the accusative, so den rather than dem.

Dativ

When to use the dative

The indirect object. Who receives.

The dative marks the person something is done to or for: ich gebe dem Kind ein Buch. All four articles change: dem, der, dem, den, and plural nouns take an extra -n: mit den Kindern.

A group of verbs takes the dative where English would use a plain object, and they have to be memorised: helfen, danken, folgen, gehören, gefallen, passen, schmecken, antworten, glauben, gratulieren. Gefallen also inverts the sentence: das Buch gefällt mir is literally the book pleases me.

Das Buch gehört meiner Schwester.

The book belongs to my sister.

Wie gefällt dir die Wohnung?

How do you like the flat?

NBThe flat is the subject; you are in the dative.

Nach dem Essen gehen wir spazieren.

After dinner we’ll go for a walk.

Mistakes to avoid

What learners actually get wrong

Ich helfe dich.
Ich helfe dir.
Helfen takes the dative, always. English “help you” looks like a direct object and gives no warning, so the dative verbs have to be learned as a list rather than derived from meaning.
Ich gehe in der Stadt.
Ich gehe in die Stadt.
In is a two-way preposition: movement towards takes the accusative, position takes the dative. Ich gehe in der Stadt is grammatical and means walking around inside the city, so if you meant going into town, the article has to change.
Mit den Kinder
Mit den Kindern
Dative plural adds -n to the noun as well as changing the article, unless the plural already ends in -n or -s. It is easy to change the article and forget the noun.
Ich gebe das Buch meinen Bruder.
Ich gebe meinem Bruder das Buch.
With two objects, the person goes into the dative and normally comes first. Here both the case and the order are wrong, and they usually go wrong together.

Questions

Asked and answered

What are the nine two-way prepositions?: An, auf, hinter, in, neben, über, unter, vor, zwischen. All nine take the accusative for movement towards a place and the dative for position. The test is wohin? for where to, against wo? for where at.
Is there a trick for the dative verbs?: Not a rule, but the list is short enough to learn: helfen, danken, folgen, gehören, gefallen, passen, schmecken, antworten, glauben, gratulieren, begegnen. Many involve doing something for or to a person rather than acting on an object, which is a weak pattern but a memorable one.
Why does only the masculine change in the accusative?: Historical erosion, the other genders lost the distinction over time. It has a practical consequence worth knowing: you can produce a lot of correct German while ignoring the accusative entirely, right up until a masculine noun appears. That is why the case feels sporadic rather than systematic at first.