～ては成らない
Must not, Cannot, Should not
Structure
Explanation
While many learners are first introduced to なくてはならない, which means 'must do', the phrase てはならない on its own expresses a strong prohibition, meaning 'must not do' or 'you are forbidden from doing'. This grammar pattern is a combination of a verb's て-form, the particle は, and ならない (the negative of the verb なる). Even though ならない can have other meanings on its own, like 'not permissible' or 'unacceptable', its meaning is always 'must not' in this specific structure.
When used after a verb's て-form plus は, ならない specifically indicates a strict prohibition: 'you must not' or 'you cannot'.
- この美術館で写真を撮ってはならない。You must not take pictures in this art museum.
- 授業中にガムを噛んではならない。You must not chew gum during class.
- 危険な場所に一人で行ってはならない。You must not go to a dangerous place by yourself.
Caution
Remember that てはだめ, てはいけない, and てはならない all express prohibition and are often used interchangeably. Their main difference is the level of formality, ordered here from most casual to most formal.
- 夜おそくまで起きていてはだめだ！You shouldn't stay up so late at night!
- 図書館で大きな声で話してはいけない。You must not speak loudly in the library.
- 試験中は辞書を使ってはならない。You must not use a dictionary during the exam.
Because the ならない form carries the most formal nuance, you will encounter it most frequently in written rules, public announcements, or very polite speech.
Examples
図書館では大声で話してはならない。
You must not talk loudly in the library.
この秘密は決して誰にも言ってはならない。
You absolutely must not tell this secret to anyone.
試験中に隣の人の答えを見てはならない。
During the test, you must not look at the answers of the person next to you.
美術館の展示品に触ってはならない。
You must not touch the exhibits at the art museum.
人から受けた恩は忘れてはならない。
You must not forget the kindness you receive from others.
薬を飲んだ後は、絶対に運転してはならない。
After taking this medicine, you absolutely must not drive.
目標を達成するまで、途中で諦めてはならない。
You must not give up halfway until you've reached your goal.
ホームでは危険ですから、走ってはならない。
It's dangerous on the platform, so you must not run.
ポイ捨ては絶対にしてはならない。
You absolutely must not litter.
甘い言葉を言う人を、すぐ信用してはならない。
You must not immediately trust people who use sweet words.
関係者以外、この部屋に入ってはならない。
Unauthorized personnel must not enter this room.
このエリアでは許可なく写真を撮ってはならない。
You must not take pictures in this area without permission.