Japanese Words for Why: Difference Between なぜ, どうして and なんで The difference between なぜ (naze), どうして (doushite) and なんで (nande) is that なぜ is a more formal term for asking why and is purely an inquiry about the reason or cause of something, whereas どうして and なんで are casual terms which can be used to convey a speaker’s emotion when asking why