〜てはいけない

Meaning

〜てはいけない means must not do something or it is not allowed to do something. It expresses prohibition.

Formation

Use the て形 of a verb and add はいけない. In polite speech, use 〜てはいけません. In casual speech, 〜てはいけない or 〜ちゃいけない can be used, but 〜ちゃいけない is more casual.

Usage

Use this pattern to explain rules, restrictions, or actions that are forbidden. It is common in schools, public places, homes, and instructions.

Nuance

〜てはいけません sounds clear and rule-like. It is stronger than a simple request not to do something. Because it tells someone that an action is not allowed, it can sound strict depending on the situation.

Comparison

〜ないでください politely asks someone not to do something. 〜てはいけない says the action itself is not allowed. 〜てもいい is the opposite pattern and means the action is allowed.

Common Mistakes

A common mistake is confusing 〜てはいけない with 〜ないでください. For a rule, use 入ってはいけません. For a polite request, use 入らないでください. Also, remember that this pattern uses the て形, not the negative form.