～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!