～てはいけない
must not / prohibition
～てはいけない expresses prohibition: “you must not do X”. It is made from the て-form of a verb, the particle は, and いけない, which literally means “it won't go”, so the whole pattern says “doing X won't do”.
It is the opposite of ～なければならない: one tells you an action is required, the other tells you an action is forbidden.
1. Rules and prohibitions
Use ～てはいけない for rules, warnings, and things that are simply not allowed. The polite form is ～てはいけません.
ここに入ってはいけない。
“You must not enter here.”
- ここ = here
- に = marker for the place you move into
- 入ってはいけない（はいってはいけない）= must not enter
ここで写真を撮ってはいけません。
“You must not take photos here.”
- ここ = here
- で = marker for the place where an action happens
- 写真（しゃしん）= photo
- を = object marker
- 撮ってはいけません（とってはいけません）= must not take (polite)
2. Casual contractions: ～ちゃだめ and ～ちゃいけない
In casual speech, ては contracts to ちゃ (and では to じゃ), and いけない is often replaced by だめ (“no good”).
それを食べちゃだめ！
“Don't eat that!”
- それ = that
- を = object marker
- 食べちゃだめ（たべちゃだめ）= must not eat (casual contraction of 食べてはだめ)
How to form it
Verb て-form + は + いけない
- 入る（はいる）= to enter → 入ってはいけない（はいってはいけない）= must not enter
- 使う（つかう）= to use → 使ってはいけない（つかってはいけない）= must not use
- 食べる（たべる）= to eat → 食べてはいけない（たべてはいけない）= must not eat
Key idea
～てはいけない takes an action and declares “that won't do”. When you hear てはいけない, ちゃいけない, or ちゃだめ, someone is drawing a line: this action is not allowed.
Built on the same stem
Updated .