〜てはならない: meaning and usage

How to form it

• verb (te-form)+は+ならない
• verb (te-form)+は+なりません

How it is used

Forbids something: 'must not'. It is found mostly in rules, written warnings and statements of principle, and sounds more formal and serious than 「〜てはいけない」, the everyday choice.

Examples

1. 先生が執筆している最中は、声をかけてはならないよ。

   You mustn't talk to the teacher while they're in the middle of writing.

2. 試験中は、ほかの人と話してはならない。

   During the exam, you must not talk to anyone else.

3. 一度の失敗であきらめてはならない。

   You must not give up after a single failure.