"He found none of the hats."
Translation:Er hat keinen der Hüte gefunden.
Why "keinen" though???
Accusative masculine singular... but referring to what? - the gentive plural Hüte??
Or does "gefunden" cause some kind of dative plural case from all the way at the end there?
Good gosh - it seems I'll only ever be able to speak shirty German, and right now, I'm ok with that.
Unless I misunderstand what's going on in this sentence, there's nothing dative here. "Der Hüte" is genitive. It's not changing because of "none" (the "positive"/"negative" distinction you made), but rather because of "of". If, as was asked about elsewhere in this thread, the sentence was "He has found no hats" instead of "none of the hats", you'd use the accusative ("keine Hüte").