Must not: てはいけません

～てはいけません ~te wa ikemasen Must not

Te-form + はいけません (wa ikemasen) states a rule: you must not do it. 廊下を走ってはいけません, "Don't run in the corridor."

Level: JLPT N5, beginner
Type: The te-form
English links: prohibition, modal verbs, must vs have to

What it means

Te-form + は + いけません means "must not". Word for word, it is "if you do it, it won't go". It is the language of school rules and signs.

The は here is the particle, so you say it "wa". 走ってはいけません is "hashitte wa ikemasen".

In speech, people shorten it. 食べてはいけません becomes 食べちゃいけません, and 飲んではいけません becomes 飲んじゃいけません. With children you will hear だめ: 走っちゃだめ!

It is strong. For a softer "please don't", use the not form + でください: 走らないでください.

How to build it

Pattern	How it works
Te-form + はいけません (食べる → 食べてはいけません) taberu → tabete wa ikemasen	A firm rule. は is said "wa".
Te-form + はだめです (走る → 走ってはだめです) hashiru → hashitte wa dame desu	More direct, common in speech. 走る is Group 1.
～ちゃいけません / ～じゃいけません (食べちゃいけません, 飲んじゃいけません) tabecha ikemasen, nonja ikemasen	Spoken short forms. て + は → ちゃ, で + は → じゃ.
Not form + でください (走らないでください) hashiranai de kudasai	A softer way: "please don't".

Examples

廊下を走ってはいけません。 rouka o hashitte wa ikemasen. Don't run in the corridor.
授業中に携帯電話を使ってはいけません。 jugyouchuu ni keitai denwa o tsukatte wa ikemasen. You can't use your phone in class.
ここでたばこを吸ってはいけません。 koko de tabako o sutte wa ikemasen. You must not smoke here.
図書館で食べてはいけません。 toshokan de tabete wa ikemasen. You're not allowed to eat in the library.
ここに車を止めてはいけません。 koko ni kuruma o tomete wa ikemasen. You can't park here.

How English says it

English has many ways to say this: "You must not...", "You can't...", "You're not allowed to...", and the plain "Don't...". "Must not" is strong and formal. It suits signs and written rules. In speech, "can't" and "don't" are far more common.

English also has "don't have to", which looks similar but means something else: "it is not necessary". "You mustn't come" and "You don't have to come" are very different messages.

Why it can make English hard

"Must not" and "don't have to" look like a pair, and many students mix them up. One is a rule; the other is a choice.
Textbooks teach "must not" first, so students use it everywhere. In conversation it can sound stiff or even rude.
After "must", students sometimes add "to", because "have to" has one.

Mistakes you will hear

You don't have to run in the corridor. You must not run in the corridor. "Don't have to" means it is not necessary. A rule needs "must not" or "can't".
You must not to use your phone. You must not use your phone. After "must", use the base verb. No "to".
It is not good to smoke here. You can't smoke here. A word-for-word copy of いけません or だめ. English states the rule directly.

In the classroom

Have students write the rules for their own school in English. Then sort them: "must not" for the written rules, "can't" and "don't" for what a teacher would say.
Use two signs on the board: a red circle with a line ("must not") and a shrug ("don't have to"). Read sentences aloud, and students point to the right sign.
Show real English signs from the internet: "No smoking", "Do not enter", "Staff only". Students turn each one into a full sentence.

Practice

Try each one, then open it to check.

1. Fill the gap: ここで写真を撮っ＿いけません。 (You must not take photos here.)

Answer: ては

Te-form + は + いけません. Say the は as "wa".
2. Make the rule: 走る

Answer: 走ってはいけません

走る looks like Group 2, but it is Group 1, so 走って.
3. A student writes "In the library, you don't have to talk." The student means it is a rule. Fix it.

Answer: In the library, you must not talk. (or: you can't talk.)

"Don't have to" means "not necessary". A rule needs "must not" or "can't".
4. Translate: 教室で食べてはいけません。

Answer: You can't eat in the classroom. (or: You must not eat in the classroom.)

てはいけません is a rule. "Can't" is the natural spoken English.