There are various ways to write sentence with "nandemo" and "nantomo". I'll try to answer the difference between "nandemo nai / なんでもない" and "nantomo nai / なんともない" "nandemo nai / なんでもない" Person A : You seem a bit down today. Are you OK? What happened? : 今日は元気がないようだけど。大丈夫？何かあった？ Person B : Nothing. / Don't care. 　　　　　　 : なんでもない This is sort of mental question, and Person B doesn't want to talk about oneself to Person A. "nantomo nai / なんともない" Person A : You've been coughing all day. Are you OK? : 1日中せきをしていたけど、大丈夫？ Person B : No problem. / Don't worry. : なんともない（よ） This is sort of physical question, and Person B doesn't want to make Person A worry about Person B. ------------------ Hope this will help :)