てはいけない is used in Japanese to express that (A) ‘cannot’, or ‘must not’ be done. It is the combination of a verb in
て form, the
は particle, and the negative
potential form of
行(い)く (to be able to go). In this way, it literally means ‘(A) cannot/is not able to go’.
-
タクシーの扉(とびら)を自分(じぶん)で開(あ)けてはいけない。
You must not open the taxi door by yourself.
-
子供(こども)の前(まえ)でタバコを吸(す)ってはいけません。
You must not smoke cigarettes in front of children.
Although
は can be dropped from many phrases and expressions, the
は in this particular grammar point is usually not. This is because
いけない would then become the second action in a sequence of events (the usual function of
て form). However, to make this more casual,
ては is often changed to ちゃ (ては becomes ちゃ), or じゃ (では becomes じゃ), as this is easier to say.
-
危(あぶ)ない場所(ばしょ)に行(い)っちゃいけない。
You must not go to dangerous places.
-
旗(はた)を踏(ふ)んじゃいけないよ。
You must not step on a flag.
Apart from いけない; ならない and だめ are also frequently used to get across the same meaning. However, they are used in different situations.
いけない - Fairly neutral. Used in both spoken and written language.
ならない - Fairly formal. Used mostly in written language.
だめ - Very casual. Used almost exclusively in spoken language.