Grammar › Questions › どうして・なぜ・なんで

Grammar · why

どうして・なぜ・なんで

Three words for "why". They mean the same thing — the difference is register. Pick the one that matches who you're talking to.

The short version

Same question, three levels of formality. なぜ is the most formal — writing, news, analysis. どうして is the neutral middle, fine spoken or written. なんで is casual and conversational. All three often get answered with から ("because…").

WordRegisterWhere you hear it
formalwriting, news, analytical
neutralspoken & written, all-round
casualfriends, family, chatting

どうして — the safe middle

The default "why" — polite enough for most situations, natural in conversation.

I don't know why. (どうして + か = "the why of it")
▶ Japanese with Shun · Ep18 · 0:55 — hear it →

なんで — casual, spoken

Among friends, なんで is the everyday "why / how come". It's the one you'll hear most in relaxed talk.

Why, I wonder. (なんで + かな = musing "I wonder why")
▶ Nihongo con Teppei · #1556 田舎日記① · 6:22 — hear it →

なぜ — formal, written

なぜ is crisp and bookish — presentations, essays, headlines. In speech it can sound a bit stiff, which is exactly its job.

The reason is… (なぜかというと — a set phrase introducing a reason)
▶ Let's Talk in Japanese! · ep379 · 2:05 — hear it →

Watch out

🗣 They mix in the same breath. Because they're synonyms, speakers even chain them for emphasis or to soften a blunt なぜ into a chattier なんで — as in なぜ、なんでですかね ("why… how come, I wonder?").
Why… how come, I wonder. (formal なぜ slid into casual なんで)
▶ Nihongo con Teppei Z · #202 · 5:49 — hear it →
Match the register. なんで with a boss or in keigo sounds too casual; なぜ among close friends sounds oddly formal. When in doubt, どうして is safe almost anywhere. (One aside: なんで can also be read literally as "by what means" — context makes clear which is meant.)
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Next: Question words — どんな・どこ・だれ → · から・ので — because → · All grammar

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