German has four cases. A case may determine the particular adjective, adjective ending, pronoun, and noun ending to use. If there is a definite article, the case is often easier to recognise.

The nominative case is used in reference to the subject of a sentence.

Der Mann / Die Frau / Das Kind isst. (The man / the woman / the child is eating.)

The accusative case is used in reference to the direct object of a sentence.

Ich sehe den Mann / die Frau / das Kind. (I see the man / the woman / the child.)

The dative case is used in reference to the indirect object of a sentence.

Er gibt dem Mann / der Frau / dem Kind den Löffel. (He gives the spoon to the man / the woman / the child.)

The genitive case is used in reference to a possessed object of a sentence.

das Buch des Mannes / der Frau / des Kindes (the man's / woman's / child's book)

To determine the case of a noun or pronoun in German, use the following steps, in order.

Determining Cases

• If the noun or pronoun is a subject, it takes the nominative case. If the noun is an object, it takes either the accusative, dative or genitive case.
• If the expression contains a dative, accusative or genitive preposition, the case of the noun or pronoun takes the case of that preposition.
• If the expression contains a two-way preposition, if the verb is transitive, the expression takes the accusative case. If the verb is intransitive, the expression takes the dative case.
• If the expression contains no prepositions, the expression takes the accusative case if the verb is intransitive, and the dative case if the verb is transitive. (see also Prepositions and Postpositions)
• In some cases, a noun or pronoun will take the genitive case, if it is possessed by the subject, or if the verb implies possession.

What are cases for?

In English, and many other languages, you know what role a noun plays from its place in the sentence. For example:

The dog bit the man

Here, you know that the man has bite-marks on his leg.

The man bit the dog.

Here, surprisingly, the dog has the bite-marks.

In German, you can change the word order around as you like. You can write:

Der Hund biss den Mann (The dog bit the man)

or

Den Mann biss der Hund (The dog bit the man)

These are both the "unsurprising" version where the man has teeth-marks. You can see that because in both sentences, it says "den Mann", not "der Mann". "Den Mann" is the accusative form which means that the person is the one bitten, not the biter. In both cases, the dog is "der Hund", making it the biter. "The man bit the dog" would be "Der Mann biss den Hund" or "Den Hund biss der Mann".

So while English uses word order to tell us what is the subject (here, the biter) and what is the object (here, the bitten), German uses cases to give us this important information. This allows German to have the advantage over English of being able to stress the object or the subject of a sentence by changing the word order (normally the first noun is the stressed part).