Prepositional Phrases and Verbvalenz

Now we are ready for a better understanding of prepositional complements. We said that the preposition auf can be translated on, in, at, by, onto, and it takes the accusative when there is a movement involved, the dative when a static relationship is described. Now consider three verbs that are regularly used with auf + accusative as a prepositional complement:

warten auf + acc. - to wait for
sich freuen auf + acc. - to look forward to
sich konzentrieren auf + acc. - to focus on

You have three aufs in German, but you have to translate them with idioms using the English prepositions for, to, and on. Auf does not "mean" for or to here - the preposition in every case is just providing the verb with a special kind of movement towards the object.

There are various ways of thinking about this need of the verb for a prepositional phrase to rule, or to complement it. In German, one speaks of 'Verbvalenz'. That means verbs sometimes demand the presence of one or more objects in order to be used in a specific meaning.

Let's have a look at the following sentences:

Sie hängt das Bild von der Wand ab.
Unsre Ferienpläne hängen von den Ferienplänen unsrer Kinder ab.

Both have the same verb and the same preposition. However, they translate quite differently:

She takes the picture down from the wall.
The plans for our holidays depend on the holiday planning of our children.

Well, von der Wand in the first sentence is a prepositional phrase, whereas von den Ferienplänen unsrer Kinder is a prepositional complement that changes the meaning of abhängen.

Now, try to take the prepositional phrase and the prepositional complement out of these sentences and see what you get:

Sie hängt das Bild ab.
*Unsre Ferienpläne hängen ab.

Clearly, the first sentence makes sense and means: She takes the picture down. The second sentence, however, is incomplete and makes no sense (that's what the * means).

Why? When a verb uses a prepositional complement to change its meaning, you cannot omit the prepositional object without changing the verb's sense (and making nonsense, usually, of the statement).

Verbs can drive you crazy! Not so the prepositional phrases. In most cases you use them because they are needed to give a proper account of the events you are talking about, but they don't have any effect on the rest of the syntax or sense of the sentence.