The preposition "in", like several other prepositions is followed by both the accusative and dative cases, depending upon the sense of the sentence:
If the sentence involves movement ("into" in English) then the accusative is used.
If the sentence involves position ("in" in English) then the dative case is used.
| Masculine | Feminine | Neuter | Plural | |
| Movement = Accusative | in den | in die | ins (= in das) | in die |
| Position = Dative | im (= in dem) | in der | im (= in dem) | in den |
Examples:
Max geht in die Bäckerei. The verb "goes" shows movement, so the accusative is used - Max moves through the door INTO the baker's shop.
Max kauft ein Brötchen in der Bäckerei. The verb "buys" does not show movement, rather position, so the dative is used. Max buys bread rolls IN the baker's shop.
Um ... zu ... clauses add information to a sentence and tell us why something is done. In English we might say "in order to", or more likely just "to".
Example:
Max geht in die Bäckerei. Er kauft Brötchen in der Bäckerei.
Using an um ... zu ... clause we can combine these two sentences into one:
Max geht in die Bäckerei, um Brötchen zu kaufen.
More examples:
Ich gehe zum Park, um mit meinen Freunden Fußball zu spielen.
Wir gehen in die Stadt, um ins Kino zu gehen.
Mein Bruder muss zu Hause bleiben, um seine Hausaufgaben zu machen.
Ich arbeite in einem Geschäft, um Geld zu verdienen.