아니오 vs. 아니요
I'm frightening ;-) my poor grey matter by trying to memorize the Korean words I learn.
Now I've come across a puzzle: On Memrise, I found 아니요 for "no", but in my book, it says 아니오.
I checked other sources on the Internet, the first agreed with my book, another one agreed with Memrise.
Now I'm confused: Are both versions permissible? I thought that, given the Korean honorific system, maybe one is more formal than the other?
I would be really grateful for a clarification. Thank you!
They are both correct and different. 아니요 means no, and 아니오 means "(It is) not." i.e. it's a sentence. Since 아니오 is in 하오체 which you probably would never see anyone use these days, you can safely forget it. Use its 합쇼체, 해요체, and 해체 counterparts instead, 아닙니다, 아니에요, and 아니야.
(Though 아니오 is grammatical, I don't think the book intended to teach 하오체. So chances are the book is wrong; put it aside and learn with Duolingo!)