だい (informal WH-question)

• 読み: だい
• ローマ字: dai
• 形: WH-word + ～ + だい

意味

A sentence-final particle used in informal male speech to mark questions containing an interrogative word (what, where, who, etc.). It adds a casual, familiar tone to information questions.

だい is the information-question counterpart to かい. While かい marks yes-no questions, だい marks questions that contain an interrogative word such as 何, どこ, だれ, いつ, or どう. Like かい, it is primarily used by male speakers and conveys a warm, approachable tone. だい typically attaches after a noun or na-adjective (which would normally end in だ) at the end of the sentence, effectively replacing the plain だ. It is most natural in questions structured as ～は何だい, ～はどこだい, etc. Learners sometimes confuse だい with かい; the key distinction is that だい appears specifically with WH-words. だい is limited to casual spoken contexts and would sound out of place in polite or formal speech.

例文

1. お名前は何だい。
2. 次の休みはいつだい。
3. トイレはどこだい。

使い方ガイド

場面: spoken, everyday

トーン: friendly

正しい言い方

• 今日の予定は何だい。
• 一番好きな映画は何だい。
• どこに行きたいんだい。

避ける言い方

• 先生、これは何だい。(Using だい toward a superior — too casual and disrespectful) → 先生、これは何ですか。
• 明日来るだい。(Using だい for a yes-no question — だい is for WH-questions only) → 明日来るかい。

起源と歴史

だい developed from だ (the casual copula) combined with the interrogative nuance of the い suffix. Like かい, it emerged during the Edo period as part of the softened masculine question-particle system.

文化的背景

世代: Adults and elderly

社会的背景: Universal