～てはいけません (How to Say “You Must Not” in Japanese)

So you’ve learned how to say “please do” (～てください), and even how to ask, “Can I?” (～てもいい). But what if you want to say:

• ❌ “You can’t smoke here.”
• ❌ “Don’t enter.”
• ❌ “That’s not allowed!”

In Japanese, the grammar you’re looking for is ～てはいけません.

It’s the polite way to say “You must not…”, and it’s super common on signs, in rules, and in everyday situations where something’s off-limits.

In this guide, you’ll learn:

• What ～て はいけません means
• How to form it with any verb
• Real examples of it in action
• Fun practice to help you remember

Let's get started!

What Does ～て はいけません Mean?

「～て はいけません」literally means “If you do ___, it’s no good.”
But functionally, it means:

❗️ “You must not ___”
❗️ “You’re not allowed to ___”
❗️ “Don’t do ___” (polite version)

It’s formal and polite, but still firm.
You’ll see it used in rules, schools, offices, and public signs.

(PS: Did you know Japanese people like to use "no good" = "NG"? Yeah, they just say NG like, literally pronounced like エヌジー. Sorry, that was a tangent.)

How to Make the ～て はいけません Form

Super easy!

Step 1: Put the verb into the ～て form

(のむ → のんで, はいる → はいって, etc.)

Step 2: Add 「はいけません」

Examples:

• たべる → たべて → たべてはいけません
• のむ → のんで → のんではいけません
• する → してはいけません
• くる → きてはいけません

This turns your verb into a polite prohibition, a way to say “don’t” or “not allowed.”

What Does「いけません」Mean?

「いけません」comes from the verb いける (to be acceptable / okay).

So when you say:

～て はいけません
You're literally saying:
"If you do ___, it’s not acceptable."

That’s why it sounds like a rule, even though it’s grammatically polite.

いけてる and いけてない (Slang)

To help put things into context, いけてる is used as slang to mean "good" and いけてない is slangy for "not good."

And derived from this, イケメン (ikemen) ＝ いけてるめん（面）-> Nice face = good-looking (usually) guy 😍.

Real-Life Examples Using ～て はいけません

Here’s what it looks like in real life:

ここでタバコをすってはいけません。

Koko de sutte wa ikemasen. → You must not smoke here. 🚭

クラスでけいたいをつかってはいけません。

Kurasu de keitai wo tsukatte wa ikemasen. → You’re not allowed to use your phone in class. 📱

そのドアをあけてはいけません。

Sono doa wo akete wa ikemasen. → You must not open that door.

たちいりきんし！はいてはいけません！

Tachiiri kinshi! Haite wa ikemasen! → Off-limits! Don’t enter!

うそをついてはいけません。

Uso wo tsuite wa ikemasen. → You must not lie. (Classic mom line 💬)

Shorter & Casual Variations

In casual speech, you might hear:

• ～ちゃダメ
• ～じゃダメ
• ～ちゃいけない

They all mean “don’t do it,” but are less polite.

Examples:

• のんじゃダメ！ → Don’t drink it!
• すてちゃダメ → Don’t throw it away!
• はいっちゃいけない → Don’t go in

But in writing or normal polite situations, stick with ～てはいけません .

Practice Time!

Practice 1: Make Prohibiting Sentences

Turn these verbs into ～て はいけません form:

のみます → __________

つかいます → __________

はいります → __________

たべます → __________

します → __________

Answers:

のんではいけません

つかってはいけません

はいってはいけません

たべてはいけません

してはいけません

Practice 2: Translate It!

Write these in Japanese using ～て はいけません:

• You must not run here.
• You can’t take photos.
• Don’t be late!

Answers:

• ここではしってはいけません。
• しゃしんをとって は い けません。
• おくれてはいけません。

Important Cultural Tip

In Japan, rules are taken seriously, and you’ll often see ～て はいけません on public signs, especially in:

• Trains 🚆
• Temples and shrines ⛩️
• Schools 🏫
• Museums 🖼️
• Parks and events 🌳🎤

So this form is important as survival Japanese 😅

Final Recap

～てはいけません = You must not / Not allowed

• Use ～て form + はいけません
• It’s polite but firm
• Great for rules, signs, and formal speech

Examples:

• のんではいけません。→ Don’t drink.
• いってはいけません。→ You must not go.
• わすれてはいけません！→ Don’t forget!