Breakdown of Du glaubst keiner Frau.
du
you (informal singular)
die Frau
the woman
kein
no, not any
glauben
to believe
Questions & Answers about Du glaubst keiner Frau.
Why is it keiner Frau instead of keine Frau?
The verb glauben (to believe) is a special verb that requires its object to be in the dative case when you are talking about believing a person. Since Frau is a feminine noun, the negative article changes from keine to keiner in the dative case.
Would the ending change if I were talking about a man?
Yes! For masculine and neuter nouns in the dative case, the negative article ending is -em. So if you wanted to say 'You do not believe a man', it would be Du glaubst keinem Mann. The -er ending on keiner is strictly for feminine nouns in the dative case.
Wait, doesn't keiner mean 'nobody'?
keiner can mean 'nobody' when it stands completely alone. But here, it is attached to the noun Frau as a negative article. When used with a noun, it simply means 'no' or 'not a'.
Why is there no word for 'not' in the German sentence?
In English you say 'You do not believe a woman', but German handles this differently. When you want to negate a noun that would normally use 'a' or 'an', you do not use nicht (not). Instead, you use the kein family of words. The German sentence literally translates to 'You believe no woman'.