GrammarJLPT N5
→ why
Why; How
JLPT N5AdverbNeutral
なぜ is an interrogative adverb meaning "why" or, less commonly, "how." It is used to ask about the reason or cause behind an action, state, or event. Among the three common ways to say "why" in Japanese — なぜ, どうして, and なんで — なぜ carries the most neutral-to-formal tone and is frequently found in writing, news, formal speech, and composed questions. なんで is the most casual of the three and is predominantly used in everyday spoken conversation, while どうして sits in between, suitable for both spoken and written contexts. Because なぜ sounds somewhat deliberate and measured, it is often chosen when the speaker wants to convey a serious or thoughtful inquiry rather than a casual or emotional one. It is typically paired with the question particle か in formal sentences, but か can be dropped in casual speech with rising intonation. なぜ is usually written in kana alone rather than in its kanji form 何故.
Examples
Example #1
なぜ今日は学校に来なかったのですか。
Here なぜ is placed at the beginning of the sentence to ask for the reason behind someone's absence. The sentence uses the polite form with のですか, which is very natural when paired with なぜ because of its neutral-to-formal tone. The combination of なぜ and のですか creates a composed, respectful inquiry suitable for a teacher speaking to a student or similar situations.Why didn't you come to school today?
Structures
- Basic question
- なぜ + Predicate (+ か)
- Embedded question
- なぜ + Clause + か / のか + Main predicate
Common mistakes
A common mistake is using なぜ in very casual, friendly conversations where なんで would be far more natural — this can make the speaker sound overly stiff or formal. Conversely, some learners avoid なぜ entirely and rely only on なんで, which can sound too casual in writing or formal contexts. Another frequent error is confusing なぜ with なぜなら (because); なぜ asks a question while なぜなら provides a reason in response. Finally, learners sometimes forget to include か or のか when embedding a なぜ clause inside a larger sentence, producing ungrammatical constructions like 「なぜ怒っているわかりません」 instead of the correct 「なぜ怒っているかわかりません」.
Related
どうしてなんで何でどうやってなぜなら