Breakdown of Du darfst dir ein Geschenk aussuchen.
ein
a, an (eine)
du
you (informal singular)
das Geschenk
the gift
dürfen
to be allowed to, may
Questions & Answers about Du darfst dir ein Geschenk aussuchen.
Why use the dative pronoun dir instead of the accusative dich?
Because the sentence already has a direct object (ein Geschenk). In German, if a reflexive verb has a direct object (the thing being acted upon), the reflexive pronoun takes the dative case. It essentially means you are choosing a gift for yourself.
aussuchen is a separable verb. Why isn't it split apart in this sentence?
The modal verb darfst changes the standard rule. When you use a modal verb, it takes the conjugated position, and the main verb (aussuchen) is pushed to the very end of the sentence in its full, unseparated dictionary form.
Is the word dir absolutely necessary, or could I just say "Du darfst ein Geschenk aussuchen"?
People would understand you without it, but using the reflexive pronoun here is much more natural. The German phrase sich etwas aussuchen is specifically used to emphasize picking something out for oneself.
Why does dir come right after the verb instead of later in the sentence?
In German sentence structure, pronouns are "light" and like to sit as close to the conjugated verb (darfst) as possible. If you added other details to this sentence, like when or where, they would come after the pronoun dir.