How to Use 〜てはいけない

The phrase “〜てはいけない” is a common Japanese grammatical structure used to express prohibition, or things that are not allowed. It translates to “must not” or “cannot” in English. This phrase is widely used in various contexts, from giving instructions to setting rules.

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Formation of 〜てはいけない

The structure “〜てはいけない” is formed by attaching て-form of a verb to はいけない. Here’s how it works:

1. Convert the verb to its て-form.
2. Add はいけない to the end of the verb.

Example:

• 食べる (to eat) → 食べてはいけない (must not eat)
• 行く (to go) → 行ってはいけない (must not go)

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Situations Where “〜てはいけない” is Used

1. Rules and Regulations
   Used to express prohibitions in formal and informal rules:
   • 学校で携帯電話を使ってはいけない。
     (You must not use mobile phones at school.)
   • ここでタバコを吸ってはいけません。
     (You must not smoke here.)
2. Giving Orders or Instructions
   Often used in scenarios where instructions need to be clear:
   • 試験中に話してはいけない。
     (You must not talk during the exam.)
   • このドアを開けてはいけません。
     (You must not open this door.)
3. Moral or Ethical Prohibitions
   Refers to socially unacceptable behaviors:
   • 他人のものを勝手に使ってはいけない。
     (You must not use someone else’s belongings without permission.)
   • 嘘をついてはいけません。
     (You must not lie.)
4. Safety Warnings
   Used to highlight actions that could lead to danger:
   • この薬を飲んでお酒を飲んではいけません。
     (You must not drink alcohol after taking this medicine.)
   • 火のそばで遊んではいけない。
     (You must not play near fire.)
5. Expressing Social Norms
   Indicates socially expected behaviors or taboos:
   • ご飯を食べながらしゃべってはいけません。
     (You must not talk while eating.)
6. Parent-Child or Teacher-Student Scenarios
   Frequently used in educational or authoritative contexts:
   • 遅くまでテレビを見てはいけない。
     (You must not watch TV until late.)
   • 宿題を忘れてはいけません。
     (You must not forget your homework.)

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Points to Remember

1. Polite Variations
   In formal or polite speech, いけない can be replaced with いけません:
   • ここに入ってはいけません。
     (You must not enter here.)
2. Casual Variations
   In casual speech, てはいけない may become ちゃいけない or じゃいけない:
   • そんなことしちゃいけないよ！
     (You shouldn’t do that!)
3. Cultural Context
   Understanding when to use “〜てはいけない” depends on the context. Japanese culture often emphasizes politeness and indirectness. Therefore, use polite forms in formal settings to avoid sounding harsh.

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Examples of Verbs and Usage

Verb (Dictionary Form)	て-Form	Usage Example
飲む (to drink)	飲んで	お酒を飲んではいけない。(You must not drink alcohol.)
遊ぶ (to play)	遊んで	道路で遊んではいけない。(You must not play on the road.)
書く (to write)	書いて	壁に書いてはいけません。(You must not write on the wall.)
行く (to go)	行って	危険な場所に行ってはいけない。(You must not go to dangerous places.)
話す (to talk)	話して	授業中に話してはいけません。(You must not talk during class.)

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List of Situations for “〜てはいけない”

1. At school (e.g., no phones, no talking during tests)
2. At work (e.g., no eating at desks, no accessing unauthorized files)
3. Public spaces (e.g., no littering, no smoking in non-smoking zones)
4. During social interactions (e.g., no interrupting others, no offensive comments)
5. While driving (e.g., no using phones, no speeding)
6. At home (e.g., no playing with dangerous tools, no staying up too late)
7. With safety rules (e.g., no entering restricted areas, no consuming certain substances)

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By understanding and mastering the use of “〜てはいけない,” you can effectively communicate prohibitions and rules in Japanese. This structure is crucial for clear, polite, and culturally appropriate expressions in both written and spoken Japanese.

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