modality N5 common casual
〜ちゃいけない — must not ~
〜ちゃいけない ・ ちゃいけない
Builds on て形
Meaning
- must not ~ / you can't ~ — casual contraction of 〜てはいけない (prohibition)
Key sentence
ここで遊んじゃいけない。
You can't play here.
Formation
| Attaches to | Form | Example |
|---|---|---|
| verb (て-form, contracted) | ては → ちゃ; では → じゃ, then + いけない／だめ | 見て + は → 見ちゃ / 飲んで + は → 飲んじゃ |
Examples
授業中にスマホを見ちゃいけないよ。
You mustn't look at your phone during class.
そんなこと、人に言っちゃいけない。
You can't go telling people that.
まだ食べちゃだめだよ。
You can't eat it yet.
When you can't use it
- Verbs whose て-form is voiced (で) contract to じゃ, not ちゃ: 飲んでは → 飲んじゃ, 死んでは → 死んじゃ. Match the contraction to the て/で of the base verb.
Easily confused with
See 〜ちゃいけない in real sentences
Jengo shows 〜ちゃいけない the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.
Study it in JengoSources Compiled from published Japanese grammar references.