Why is this not an accusative case? If it were "Ich esse den Mann" (cannibal sentence, sorry), then it would've been accusative, right? Is danken an exception verb?
Some verbs in German imply a certain case. 'Danken' implies the dative. http://german.about.com/library/verbs/blverb_dativ.htm
Thanks for your help! The DuoLingo tips section said "Ich danke ihr" is correct instead of "ich danke sie," but did a terrible job explaining--it didn't even say that "danken" implies dative. Thank you!
I think it's because you "give" thanks to the man. To thank the man would mean you do something to him, whereas giving thanks to the man makes it dative.
Because the German verb is "jemandem danken", and it requires the dative object. So it would be best to memorize verbs and the case of its object.
Because the means "der" and "that/this" means dieser. It is not a specific man in the sentence so you can't use that or this