JapaneseJLPT
JLPT N5 grammar · Chapter 15

～ちゃいけない・～じゃいけない

Casual way to say “must not”

You’ll be able to tell friends casually that something isn’t allowed.

Illustration of the scene described by You mustn’t take photos here.
Read it first

ここで写真しゃしんを撮とっちゃいけない。

koko de shashin o toccha ikenai.

What do you think this sentence means?

You mustn’t take photos here.

Why it means that

Say “must not” in casual speech

These are casual contractions of ～てはいけない and ～ではいけない. Use ちゃ after a て-form and じゃ after a で-form.

Examples

夜よる遅おそくに電話でんわしちゃいけないよ。

yoru osoku ni denwa shiccha ikenai yo.

You shouldn't make phone calls late at night.

川かわで泳およいじゃいけない。

kawa de oyoija ikenai.

You must not swim in the river.

How it is built

ては → ちゃ

When the て-form ends in て, contract ては to ちゃ before いけない.

Verb stem+ては+いけない→Verb stem+ちゃいけない
Examples

食たべてはいけない → 食たべちゃいけない

tabete wa ikenai → tabecha ikenai

must not eat → casual contraction

入はいってはいけない → 入はいっちゃいけない

haitte wa ikenai → haiccha ikenai

must not enter → casual contraction

見みてはいけない → 見みちゃいけない

mite wa ikenai → micha ikenai

must not look → casual contraction

How it is built

では → じゃ

When the て-form ends in で, contract では to じゃ before いけない.

Verb stem+では+いけない→Verb stem+じゃいけない
Examples

飲のんではいけない → 飲のんじゃいけない

nonde wa ikenai → nonja ikenai

must not drink → casual contraction

遊あそんではいけない → 遊あそんじゃいけない

asonde wa ikenai → asonja ikenai

must not play → casual contraction

泳およいではいけない → 泳およいじゃいけない

oyoide wa ikenai → oyoija ikenai

must not swim → casual contraction

Compare

～てはいけません vs ～ちゃいけない・～じゃいけない

Both express prohibition (“must not”). Use the casual contractions with friends and family, and the full forms for polite speech and written rules.

  • Casual (ちゃ)

    ここで走はしっちゃいけない。

    koko de hashiccha ikenai.

    You mustn’t run here.

    Casual warning to a friend or classmate.

  • Polite (ては)

    ここで走はしってはいけません。

    koko de hashitte wa ikemasen.

    You must not run here.

    Formal prohibition, used for public rules and signs.

  • Casual (じゃ)

    川かわで泳およいじゃいけない。

    kawa de oyoija ikenai.

    You mustn’t swim in the river.

    Casual warning to a friend or family member.

  • Polite (では)

    川かわで泳およいではいけません。

    kawa de oyoide wa ikemasen.

    You must not swim in the river.

    Formal prohibition, used on warning signs and in official notices.

Examples

ここで写真しゃしんを撮とっちゃいけない。

koko de shashin o toccha ikenai.

You must not take photos here.

このケーキを食べたべちゃいけない。

kono keeki o tabecha ikenai.

You must not eat this cake.

その部屋へやに入っはいっちゃいけない。

sono heya ni haiccha ikenai.

You must not enter that room.

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