How to Say “You Must Not” in Japanese | Using te-form + wa ikemasen（〜てはいけません）

level1 (N5)

Video

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How to Say “You Must Not” in Japanese | Using te-form + wa ikemasen（〜てはいけません）
Source: gokigen japanese official YouTube Channel

Introduction

Want to say things like:

  • “You must not smoke.”
  • “You must not talk in the library.”
  • “You must not forget your homework.”

In Japanese, the expression 〜てはいけません is used to clearly prohibit actions. Whether you’re reading a sign in Japan or giving a rule to someone, this is the go-to grammar point for saying “Don’t do that!”

Let’s learn how to use this powerful and polite form of prohibition in Japanese.

1. What Does 〜てはいけません Mean?

V-てはいけません means:

  • You must not do 〜
  • It is not allowed to 〜
  • Don’t do 〜 (polite)

It combines the て-form of a verb with はいけません, which literally means “you can’t go on (doing something)” — but in actual use, it functions as “you must not.”

ここで写真しゃしんを撮とってはいけません。
No photography allowed here.

2. How to Form the Sentence

The structure is simple: Verb (in て-form) + はいけません

Example Conjugations:

Verbて-formFinal SentenceMeaning
寝ねる寝て寝てはいけませんYou must not sleep
話はなす話して話してはいけませんYou must not talk
飲のむ飲んで飲んではいけませんYou must not drink
忘わすれる忘れて忘れてはいけませんYou must not forget
開あける開けて開けてはいけませんYou must not open

3. When to Use This Grammar

Use 〜てはいけません when:

  • You want to prohibit an action
  • You’re talking about school, work, or public rules
  • You need to be polite but clear

It’s commonly found on signs, in instructions, and in classroom settings.

4. Real-Life Examples

JapaneseEnglish
学校がっこうで寝ねてはいけません。You must not sleep at school.
お酒さけを飲のんではいけません。You must not drink alcohol.
ドアを開あけてはいけません。You must not open the door.
宿題しゅくだいを忘わすれてはいけません。You must not forget your homework.
自転車じてんしゃに乗のってはいけません。You must not ride a bicycle.

5. Practice: Can You Say It?

Convert the following into 〜てはいけません form:

  1. 座すわる → 座ってはいけません
  2. 話はなす → 話してはいけません
  3. 休やすむ → 休んではいけません
  4. 忘わすれる → 忘れてはいけません
  5. 開あける → 開けてはいけません
  6. ゲームをする → ゲームをしてはいけません

6. Asking and Answering with 〜てはいけません

You can answer questions about permission like this:

QuestionAnswer
学校がっこうでゲームをしてもいいですか。
Is it okay to play games at school?		いいえ、してはいけません。
No, you must not do that.
図書館としょかんで話はなしてもいいですか。
Is it okay to talk in the library?		いいえ、話してはいけません。
No, you must not talk.
子こどもはお酒さけを飲のんでもいいですか。
Is it okay for children to drink alcohol?		いいえ、飲んではいけません。
No, they must not drink (it).

7. FAQ – Frequently Asked Questions

Q
What’s the casual version?
A
  • 〜ちゃだめ (Use the て form but remove て. Example: たべる→たべて→たべちゃだめ)
    • そのクッキーは食たべちゃだめだよ！ / Don’t eat those cookies!
  • 〜じゃだめ (If the て form is で. Example: のむ→のんで→のんじゃだめ)
    • 未成年みせいねんはお酒さけを飲のんじゃだめ！ / Minors should not drink alcohol!
Q
How strong is the prohibition with “~te wa ikemasen”? How does it differ from other prohibition expressions like “~naide kudasai”?
A

“~te wa ikemasen” expresses a relatively clear “prohibition,” often used for rules, regulations, or by a superior towards a subordinate. It clearly conveys something one must not do. On the other hand, “~naide kudasai” takes the form of a request, “Please stop doing ~” or “Please don’t do ~,” carrying a nuance of a more polite and milder prohibition or request.

Q
Although “~te wa ikemasen” is a polite expression, can it sometimes give a strict impression?
A

Although it uses the polite form (desu/masu style), because it directly conveys prohibition, it can potentially sound a bit strict or cold depending on the situation and the listener.

It should especially be avoided when speaking to someone of equal or higher status. In situations requiring more consideration, using softer expressions like “~naide itadakemasu ka” (Could I possibly ask you not to do ~?) or “~ wa go-enryo kudasai” (Please refrain from ~) might be more appropriate.

Q
What’s the opposite of 〜てはいけません？
A

It’s 〜てもいいです, which means “It’s okay to do 〜.”
Example: 写真しゃしんを撮とってもいいです。 = You may take a picture.

Conclusion

Now you can say what is not allowed in Japanese!

✅ Use 〜てはいけません to express prohibition
✅ Master the て-form of verbs to build correct sentences
✅ Be clear and polite when giving rules or instructions

🎯 Try writing 3 classroom rules using this pattern!

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Our native Japanese instructors at gokigen japanese can help you perfect your pronunciation and learn real-life usage.

Whether you’re completely new to Japanese or looking to refine your skills, book a one-on-one session.


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    Japanese native and language educator with about 10 years of experience teaching and developing courses and materials.
    She studied and taught in 5 different countries. Her most recent teaching role was at University of Pennsylvania in the U.S.
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    Education: M.A. in Japanese pedagogy, Purdue University. B.A from the school of Japanese language and culture, Tsukuba University.