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
(to be able to go). In this way, it literally means ‘(A) cannot/is not able to go’.
You must not open the taxi door by yourself.
You must not smoke cigarettes in front of children.
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.
You must not go to dangerous places.
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.