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JLPT N3 · Reason & cause

てはいけないから (te wa ikenai kara)

～てはいけないから — “because we mustn't ～”

In short · Verb te-form + はいけない + から gives a reason based on a prohibition: “because I/we must not ～.” The speaker explains an action taken in order to avoid something bad. The second half is what to do to avoid it.
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Pattern

  • 動詞て形 ＋ はいけない ＋ から、〜 te-form + はいけない + から (遅刻してはいけないから)

Meaning and connection

～てはいけない is “must not ～,” and から gives the reason. Together they say: “Because it would be bad to ～, I do this.” 遅刻してはいけないから、早めに出ましょう.

How it is used

The second half is a countermeasure or an action to prevent the bad result: 早めに出る, 家で休む, 水をやる. The listener sees both the danger and the response.

Natural alternatives

In writing, ～ないように (so as not to ～) is more common and smooth: 遅刻しないように、早めに出ましょう. ～てはいけないから is more direct and strong.

Examples

  • 遅刻（ちこく）してはいけないから、早（はや）めに出（で）ましょう。

    Chikoku shite wa ikenai kara, hayame ni demashō.

    Because we mustn't be late, let's leave early.

  • 風邪（かぜ）をうつしてはいけないから、今日（きょう）は家（いえ）で休（やす）む。

    Kaze o utsushite wa ikenai kara, kyō wa ie de yasumu.

    Because I mustn't pass on my cold, I'll rest at home today.

  • 花（はな）を枯（か）らしてはいけないから、毎朝（まいあさ）水（みず）をやっている。

    Hana o karashite wa ikenai kara, maiasa mizu o yatte iru.

    Because I mustn't let the flowers wither, I water them every morning.

Common mistakes

  • Do not drop は: ～てはいけない (or the casual ～ちゃいけない). Plain ～ていけない is wrong.
  • から is plain and direct. To a superior, use ～てはいけませんので or ～ないように.

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