Case Overview: Why is the Noun in the Sentence?

You have at this point learned a variety of rules about case, which seem sometimes to contradict each other. The key is that any given noun will be EITHER

the subject, direct object or indirect object of a verb, OR
the object of a preposition. Prepositional objects are just that: objects of a preposition, NOT subject or object of a verb!

In order to know which rule to apply to a given noun, you need first to decide how that noun got into the sentence.

Verbs

…can usually bring only two nouns into the sentence: the subject (person doing the action) and the direct object (person or thing “being verbed”). The subject will be Nominative, the direct object is in the Accusative:

Eine Maschine [Nom] produziert den SPAM [Acc].
Der SPAM [Nom] verpestet [=filthily pollutes] die Umwelt [Acc].
Später genießt [=savors] der Deutschprofessor [Nom] den SPAM [Acc].
Dann schläft er [Nom].

Some verbs can have two objects, one direct (Accusative) and one indirect (Dative). In this case, the person or thing “being verbed” is still the direct, Accusative object, while the recipient or beneficiary of the action (usually a person) is the indirect, Dative object:

Heute früh hat Marlene Dietrich [Nom] mir [Dat] einen Kuss [Acc] gegeben.
Ich [Nom] zeige meinen Freunden [Dat] den Lippenabdruck [lip prints, Acc].
Sie [Nom] empfehlen [=recommend] mir [Dat] einen Psychiater [Acc].

Finally, a few special verbs are “Dative verbs”: for no good reason, the thing “being verbed” is in the Dative case for these verbs. There are only a few “Dative verbs”; the most common are danken, glauben, helfen, gefallen, gehören and schmecken and wehtun, and since you learn them specially, they should stand out to you when they come up:

Die Kriminellen [Nom] helfen dem korrupten Politiker [Dat].
Bitte glaub mir [Dat]: deine Tätowierung [Nom] gefällt mir [Dat] sehr!
Dem Seemann Popeye [Dat] schmeckt Spinat [Nom] sehr gut.

Prepositions

If each verb only brings one, two, or at most three nouns into the sentence, where do the other nouns come from? They are brought into the sentence by prepositions.

As the name “pre-positions” indicates, prepositions always come right before the noun or pronoun they bring into the sentence, and are in fact inseparable from it. They are like thumb-tacks attaching the noun to the sentence: without them, the noun would fall out (==> a preposition at the end of a sentence in German is not a preposition at all, but rather must be part of a separable verb, as in “Ich komme um 9 Uhr an.”!). Hence it is easy to tell if a noun is in a sentence because of a verb or because of a preposition:

Nach der Klasse [Dat] springe ich [Nom; not brought in by a preposition] stundenlang ohne Schuhe [Acc] mit meinen Freundinnen [Dat] auf meinem Bett [Dat].

Here, only ich is not preceded by a preposition. All the other nouns are brought into the sentence by the prepositions nach, in, mit, and auf. They are thus objects of those prepositions, and those prepositions determine their case, NOT the verb. So even though I am jumping on the bed, the bed is NOT the object of the verb springen: it is the object of the preposition auf.

If the noun is in the sentence because it is the object of a preposition, then it is easy to determine its case:

nouns following the Acusative prepositions (ohne, für, um, durch, gegen (& bis)) are in the Accusative
nouns following the Dative prepositions (aus, außer, bei, mit, nach, seit, von, zu) are in the Dative (even if the Dative preposition describes motion, like zu in “Wir gehen zum Bahnhof,” or von in “Ich komme von der Ärztin”!)
nouns following the two-way prepositions (in, auf, an, unter, über, vor, hinter, neben, zwischen) are
- Accusative: if the verb is describing a change of location: where someone or something is going or being put.
- Dative: if the verb is describing where something is located or where an action is taking place
- this is summarized by the nonsense mnemonic: “Accusative-Cruisative; Dative-Stative”

You can practice applying this with any text whatsoever: ask yourself for each noun if it is preceded by a preposition. If yes, that preposition determines its case; if not, it is there because of a verb and then the verb determines its case.

Click here for more info on prepositions

Exceptions

Time Expressions

These fall into two categories:

(1) Time expressions involving a preposition

if it is an Accusative or Dative preposition, the noun is in the Accusative or Dative accordingly:

für einen Monat [Acc], um 4 Uhr [Acc], nach Mitternacht [Dat]

if it is a two-way preposition, the noun is always in the Dative:

am Montag, in einer Woche, vor zwei Jahren

(2) Time expressions not involving prepositions

These always use Accusative:

Wir waren einen Monat in Berlin.
Von München nach Berlin sind wir sechs Stunden gefahren.
Zwei Tage haben wir bei meiner Mutter gewohnt.
Den Rest der Zeit waren wir in einem Hotel.

Genitive

In the last example above, “Den Rest der Zeit waren wir in einem Hotel,” the noun “Zeit” is in the genitive; the phrase means “the rest of the time.”

Nouns in the Genitive work quite differently and should stand out for that reason. They are in fact brought into the sentence not by a verb or a preposition, but by another noun, the thing or person “owned,” which itself may be in any of the four possible cases:

Der Hut des Mannes ist schön.
Ich möchte den Hut des Mannes kaufen.
Mit dem Hut des Mannes würde ich gut aussehen.
Die Farbe des Hutes des Mannes gefällt mir sehr.

In all of the above cases, the noun “des Mannes” is brought into the sentence by the noun “der Hut” (which itself is in a variety of cases), which the man owns. In each case “des Mannes” means “of the man,” usually expressed in English as “the man’s.”