〜次第

〜次第 (しだい) expresses "the moment A is complete, B will be done immediately": 会議が終わり次第、ご連絡します (I will contact you as soon as the meeting ends). This is a formal expression, very common in business email and communication with customers.

Formation: drop ます from the verb and add 次第 (終わり次第, でき次第); action nouns attach directly (到着次第 — as soon as [someone/something] arrives). The key grammar point: the second clause must be a DELIBERATE action by the speaker that has not yet happened — usually in the ます-form, いたします, or a request — never past tense in the second clause.

This is exactly where it contrasts with 〜たとたん: たとたん narrates the past with an unexpected event, while 次第 faces the future with a promise to "do it right away." Compared with the everyday 〜たらすぐに, 次第 is far more formal — use it when writing email to a superior or a business partner.

Examples

• 会議(かいぎ)が終(お)わり次第(しだい)、ご連絡(れんらく)いたします。

  I will contact you as soon as the meeting ends.

• 詳(くわ)しいことが分(わ)かり次第(しだい)、お知(し)らせします。

  As soon as I know the details, I will let you know.

• 準備(じゅんび)ができ次第(しだい)、出発(しゅっぱつ)しましょう。

  Let's set off as soon as we're ready.

Related patterns

• 〜たとたん（に）
• 〜てからでないと／てからでなければ