〜ないうちに

〜ないうちに expresses "do B while A hasn't happened yet" — seizing the moment to act before the situation turns unfavorable: 暗くならないうちに帰りましょう (let's head home before it gets dark). This is the negative counterpart of 〜うちに: the window being seized here is the state of "A not yet having happened."

Compared with 〜前に, which you've used since N5, the difference lies in nuance: 暗くなる前に merely states a time point neutrally, while 暗くならないうちに implies "darkness would be a problem — act now before it's too late." That's why ないうちに suits cases where you can't predict exactly when A will happen, and it often carries a slight sense of urgency.

This pattern also describes something happening before you even notice: 気がつかないうちに寝てしまった (I fell asleep before I knew it). The familiar phrase 知らないうちに (without realizing it) is exactly this use.

Examples

• 暗(くら)くならないうちに、家(いえ)に帰(かえ)りましょう。

  Let's head home before it gets dark.

• 忘(わす)れないうちに、メモしておきます。

  I'll jot it down before I forget.

• 雨(あめ)が降(ふ)らないうちに、洗濯物(せんたくもの)を入(い)れてください。

  Please bring in the laundry before it starts raining.

Related patterns

• 〜うちに
• 〜ずに