Ich glaube an dich.

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Breakdown of Ich glaube an dich.

• dich: you; (informal singular, accusative)
• glauben an: to believe in

Questions & Answers about Ich glaube an dich.

Why is the preposition an necessary in Ich glaube an dich?

Because glauben when meaning “to believe in” is a prepositional verb in German. It always combines with an plus an accusative object. Without an, the sentence would be ungrammatical (and you’d lose the sense of having faith in someone).

What case is dich here and why?

dich is the accusative form of du. German prepositions govern specific cases; in this abstract meaning, an always takes the accusative, so you must use dich, not dir.

How would I say “I believe you” in the sense of “I trust what you’re saying”?

You’d say Ich glaube dir. In that sense, glauben takes a dative object.

• Ich glaube dir = “I believe you (that you’re telling the truth).”
• Ich glaube an dich = “I believe in you / I have faith in you.”

Why can’t I just say Ich glaube dich?

Because the meaning “to believe in” requires the construction glauben an + accusative. Dropping an leaves glauben without its required preposition, so it’s simply wrong in German.