〜ちゃいけない／〜じゃいけない
Must not ~ (casual)
〜ちゃいけない and 〜じゃいけない are the casual spoken forms of 〜てはいけない, "must not ~". Parents, friends and older siblings use them to tell someone not to do something.
How to make it
| Rule | Example |
|---|---|
| Verb て-form ending in て: ては → ちゃ | 食べて → 食べちゃいけない |
| Verb て-form ending in で: では → じゃ | 飲んで → 飲んじゃいけない |
| Full form for comparison | 見てはいけない → 見ちゃいけない |
Meaning and examples
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1. Telling someone not to do something
A casual way to forbid or warn, often with よ at the end.
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ここであそんじゃいけないよ。
ここであそんじゃいけないよ。
koko de asonja ikenai yo.
You mustn't play here.
-
まだ食べちゃいけないよ。
まだたべちゃいけないよ。
mada tabecha ikenai yo.
You can't eat it yet.
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このへやに入っちゃいけない。
このへやにはいっちゃいけない。
kono heya ni haitcha ikenai.
You mustn't go into this room.
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子どもはおさけを飲んじゃいけないよ。
こどもはおさけをのんじゃいけないよ。
kodomo wa osake o nonja ikenai yo.
Children mustn't drink alcohol.
-
うそを言っちゃいけないよ。
うそをいっちゃいけないよ。
uso o itcha ikenai yo.
You mustn't tell lies.
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2. Asking casually if something is not allowed
With の？ at the end, it asks a friend or family member "Am I not allowed to ~?".
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ここでしゃしんをとっちゃいけないの？
ここでしゃしんをとっちゃいけないの？
koko de shashin o totcha ikenai no?
Aren't we allowed to take photos here?
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これ、見ちゃいけないの？
これ、みちゃいけないの？
kore, micha ikenai no?
Am I not allowed to look at this?
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Nuance
This is spoken, casual Japanese, so don't use it with teachers, customers or in writing; use 〜てはいけません or 〜ないでください instead. The change is regular: ては becomes ちゃ and では becomes じゃ. You will also hear 〜ちゃだめ, which means the same thing and is very common with children.
Compared with
〜てはいけません is the polite, full form. 〜ちゃいけない is its casual spoken contraction.
〜ないでください is a polite request not to do something. 〜ちゃいけない states a casual rule.
〜なくてはいけない means you must do something. Its casual form is 〜なくちゃ, the opposite of 〜ちゃいけない.
Common mistakes
Wrongここであそんちゃいけないよ。
Rightここであそんじゃいけないよ。
あそんで ends in で, so では becomes じゃ, not ちゃ.
Wrong（おきゃくさんに）ここで食べちゃいけないよ。
Rightここで食べないでください。
ちゃいけない is too casual for customers; use a polite form.
Practice
JLPT style: choose the best answer for （ ）.
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1「ここであそん（ ）いけないよ。」
The て-form is あそんで, so では becomes じゃ: あそんじゃいけない. ちゃ is only for て-forms ending in て, and だ and に do not make this pattern.
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2「まだ食べ（ ）いけないよ。」
The て-form is 食べて, so ては becomes ちゃ: 食べちゃいけない. じゃ is only for で-forms, and 食べる and 食べない cannot come before いけない here.
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3「子どもはおさけを飲ん（ ）いけないよ。」
飲む has the て-form 飲んで, so the contraction is 飲んじゃ. ちゃ is for て-forms ending in て, and だ and に do not make this pattern.
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4「このへやに入っ（ ）いけないよ。」
入って ends in て, so ては becomes ちゃ: 入っちゃいけない. じゃ is only for verbs whose て-form ends in で.
FAQ
What does ちゃいけない mean in Japanese?
It means "must not" or "you can't". It is the casual spoken form of てはいけない, made by shortening ては to ちゃ.
Is ちゃだめ the same as ちゃいけない?
Yes, the meaning is the same. ちゃだめ is even more casual and is very common when talking to children.
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