んだい
Meaning
A casual, masculine-sounding way to ask a question, usually with a question word, asking for an explanation or information about something.
Conjugation
V・Adjい (plain form) + んだい: Nな-adj・Noun + なんだい
Examples
Show translation
どうして君は僕に冷たいんだい？
それで、君はこれからどうするんだい？
どうしてそういう映画が好きなんだい？
おじいちゃん、何を読んでいるんだい？
昨日の夜はどこにいたんだい？
今日の試合は何時からなんだい？
grammarDetailPage.commonMistakes.title
grammarDetailPage.commonMistakes.wrong: 明日学校に行くんだい？
grammarDetailPage.commonMistakes.correct: 明日はどこに行くんだい？ / 明日学校に行くのかい？
grammarDetailPage.commonMistakes.why: んだい is normally used with a question word. For a plain yes/no question, use のかい (or んですか in polite speech).
grammarDetailPage.commonMistakes.wrong: これは何だんだい？
grammarDetailPage.commonMistakes.correct: これは何なんだい？
grammarDetailPage.commonMistakes.why: Nouns and na-adjectives need な before んだい (なんだい), not だ.
grammarDetailPage.commonMistakes.wrong: 先生、どうするんだい？
grammarDetailPage.commonMistakes.correct: 先生、どうなさるんですか？
grammarDetailPage.commonMistakes.why: んだい is casual and sounds like an older man talking to a child or an equal. It is rude or odd when addressed to a teacher, a boss or a stranger.
Key points
Used with a question word (どうして, 何, 誰, どこ, etc.) between close people or when speaking to someone younger or of equal standing. It sounds masculine, gentle or somewhat old-fashioned, and is not suitable for superiors or formal situations (use んですか instead). For yes/no questions, use のかい / んですか, not んだい.
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