also: ちゃ · ちゃあ
expression
Expresses a conditional or hypothetical situation, often with a negative or undesirable result. Used after the て-form of verbs and adjectives.
そんなことをしてはだめだ。
You must not do such a thing.
雨が降っては試合は中止だ。
If it rains, the game will be cancelled.
expression
since ...; if you are going to ...
Indicates that once an action is taken or a state is reached, a certain consequence follows; often used for giving reasons or warnings.
こうなってはもう手遅れだ。
Since it has come to this, it's too late.
やるって言ったからには、最後までやらなくては。
Since you said you'd do it, you have to see it through.
expression
one after another; repeated action
Used with verbs to indicate repetition or alternation of actions, often in the pattern 〜ては〜、〜ては〜.
彼は書いては消し、書いては消しして、なかなか手紙が書けない。
He writes and erases, writes and erases, and just can't seem to finish the letter.
expression
Attaches to the て-form to add emotional emphasis, often in negative commands or strong assertions. Common in casual speech with ちゃ.
泣いちゃだめだよ。
Don't cry.
勝手に入っちゃだめ！
Do not go in without permission!