〜てはいけない

〜てはいけない is a て-form extension that expresses must not / may not. The て-form is one of the most productive patterns in Japanese — by combining it with various helper verbs and expressions, you can express a wide range of meanings from ongoing actions to requests to sequential events.

This is an intermediate pattern used regularly in everyday Japanese conversation and writing.

When to Use#

• When prohibiting an action or stating a rule
• When telling someone that something is not allowed

When NOT to Use#

• When the meaning is closer to "may / it's okay to" — use 〜てもいい instead
• In very formal writing where a more sophisticated expression would be expected

Example Sentences#

• 会議に遅れてはいけません。 — You must not be late for the meeting.
• 許可なく帰ってはいけません。 — You must not leave work without permission.
• デスクで食べてはいけません。 — You must not eat at your desk.

Practice#

Try reading these sentences aloud, then check the translation and vocabulary:

Common Mistakes#

1. Confusing 〜てはいけない with 〜てもいい — While both are related, 〜てはいけない expresses "must not / may not" whereas 〜てもいい expresses "may / it's okay to." Pay attention to the specific nuance each pattern conveys.
2. Incorrect て-form conjugation — Make sure you correctly form the て-form of the preceding verb before attaching this pattern. Group 1 verbs have sound changes (く→いて, ぐ→いで, す→して, etc.).

Related Patterns#

• 〜てもいい (may / it's okay to) — Compare