ちゃいけない / じゃいけない

ちゃいけない / じゃいけない is the casual, spoken contraction of ～てはいけない / ～ではいけない, used to express prohibition – telling someone they must not do something. It is very common in everyday conversation, especially among friends, family, or when speaking to children.

How the contraction works

The contraction depends on the ending of the verb's て-form:

• When the て-form ends in て → ては contracts to ちゃ: たべて食べて → 食べては → 食べちゃいけない
• When the て-form ends in で → では contracts to じゃ: のんで飲んで → 飲んでは → 飲んじゃいけない

More examples of the contraction:

• いって行って → 行っちゃいけない (must not go)
• あそんで遊んで → 遊んじゃいけない (must not play)
• みて見て → 見ちゃいけない (must not look)
• しんで死んで → 死んじゃいけない (must not die)

Usage

This form is used to forbid or warn against doing something:

Polite variant

In slightly more polite casual speech, you may hear ちゃいけません / じゃいけません, which combines the contraction with the polite いけません:

Related forms

• ～てはいけない / ～ではいけない – the uncontracted, standard form (slightly more formal)
• ～てはならない / ～ではならない – a more formal/literary prohibition
• ～ちゃだめ / ～じゃだめ – another casual way to say "must not", using だめ instead of いけない