Strict Prohibition: 〜てはいけません (Rules, laws & social boundaries)

Mental Model: The Barrier Across the Path

When society, laws, or safety guidelines erect an absolute boundary against an action, Japanese uses: [Verb in て-form] + は + いけません

Linguistically, this construction is built from three distinct elements: • 〜て: The action under consideration. • は (pronounced wa): The topic particle, establishing the action as the target of evaluation. • いけません: The polite negative potential of 行く (iku, to go), literally meaning “it cannot go forward” or “it will not do”.

Put together, the sentence states: “As for doing [action], it cannot proceed / it won't do.”

Because it carries clear authority, it is the primary pattern used on warning signs in museums, instructions from doctors, rules enforced by schoolteachers, and safety protocols in public spaces.

The Voiced Euphonic Shift: ではいけません

Remember that verbs ending in む, ぶ, or ぬ end their て-form with a voiced nasal: 〜んで. When attaching the topic marker は to a voiced で, the particle softens:

• Verbs ending in て: Take 〜てはいけません:
• 食べる → 食べてはいけません (”You must not eat”)
• 撮る → 撮ってはいけません (”You must not take photos”)

• Verbs ending in で: Take 〜ではいけません:
• 飲む → 飲んではいけません (”You must not drink”)
• 遊ぶ → 遊んではいけません (”You must not fool around”)

Conversational Contractions: Casual Prohibitions

In everyday spoken Japanese among family members and close friends, the formal 〜てはいけません contracts into punchy, immediate forms:

• The ては contraction to ちゃ:
• 入ってはいけない → 入っちゃだめ / 入っちゃいけない (”Don't go in!”)
• 食べてはいけない → 食べちゃだめ (”Don't eat that!”)

• The では contraction to じゃ:
• 飲んではいけない → 飲んじゃだめ (”Don't drink that!”)
• 遊んではいけない → 遊んじゃだめ (”Don't mess around!”)

Sociolinguistic Pitfall: Who Can You Forbid?

Because 〜てはいけません expresses top-down authority, you must never use it toward customers, guests, or superiors:

• Telling a customer *ここでタバコを吸ってはいけません sounds inappropriately patronizing and confrontational.
• In professional service Japanese, businesses use humble, indirect formulas instead: 恐れ入りますが、こちらでの喫煙はご遠慮ください。 (”We humbly ask that you refrain from smoking here.”)