～てはいけない
Must not, May not
Structure
Explanation
てはいけない is a Japanese grammar pattern used to state that an action is forbidden or not permitted. It's constructed with the て form of a verb, the topic particle は, and いけない, the negative potential form of the verb 行く (to go). Literally, this can be understood as 'if you do (verb), it will not go well', which implies prohibition.
- それに触ってはいけない。You must not touch that.
- 廊下を走ってはいけません。You must not run in the hallway.
The particle は is a crucial component of this grammar and is rarely omitted. Leaving it out would change the meaning to a simple sequence of actions (verb-て, いけない). In casual conversation, however, ては frequently contracts to ちゃ (ては becomes ちゃ), and では contracts to じゃ (では becomes じゃ), which makes pronunciation smoother.
- 宿題を忘れちゃいけない。You mustn't forget your homework.
- それを飲んじゃいけないよ。You mustn't drink that.
Caution
In addition to いけない, the words ならない and だめ can be used to express the same idea of prohibition. Each one, however, carries a different nuance and is appropriate for different contexts.
いけない - Generally neutral. It is suitable for both spoken and written Japanese.
ならない - More formal. Primarily found in written contexts like rules or regulations.
だめ - Highly informal. Almost always used in casual speech, often when speaking to children or close friends.
Examples
この絵に触ってはいけません。
You must not touch this painting.
廊下を走ってはいけない。
You must not run in the hallway.
図書館で携帯電話を使ってはいけません。
You must not use your cell phone in the library.
大事なことを忘れてはいけない。
You must not forget important things.
ここに車を止めてはいけません。
You must not park your car here.
そのドアを開けてはいけない。
You must not open that door.
試験中に話してはいけません。
You must not talk during the exam.
建物の中でタバコを吸ってはいけない。
You must not smoke inside the building.
公園にゴミを捨ててはいけません。
You must not throw away trash in the park.
この椅子に座ってはいけない。
You must not sit on this chair.
明日の会議に遅れてはいけません。
You must not be late for tomorrow's meeting.
最後まで諦めてはいけない。
You must not give up until the very end.