～てはいけない – Expressing Rules and ‘Must Not’ in Japanese [JLPT N5]

Quick Summary

• Meaning: ～てはいけない (~te wa ikenai) means “must not” or “you are not allowed to.” It is used to give strong prohibition.
• How to Use: Attach ～てはいけない to the V-て form of a verb.

• Example:
• 先生のプリンを食べてはいけません。
• Sensei no purin o tabete wa ikemasen.
• You must not eat the teacher’s pudding.

Overview

The grammar pattern ～てはいけない (~te wa ikenai) is one of the most common ways to say that something is not allowed in Japanese. It is often translated as “must not,” “cannot,” or “you may not.”

You use this pattern when you want to say that an action is forbidden by rules, common sense, or the situation. For example, “You must not run in the library,” or “We must not tell this secret.” It is stronger than just “don’t do it”; it feels more like a rule or a serious warning.

In everyday conversation, you will hear both the plain form ～てはいけない (~te wa ikenai) and the more polite form ～てはいけません (~te wa ikemasen). The meaning is the same; only the level of politeness changes.

Some typical situations where you use ～てはいけない:

• Talking about rules at school, work, or home
• Explaining laws or public rules (for example, in a park or on a train)
• Giving a strong warning to a friend, child, or yourself

For example, if you see your friend trying to give spicy curry to a tiny hamster, you might say:

• ハムスターにカレーをあげてはいけないよ。
• Hamusutā ni karē o agete wa ikenai yo.
• You must not give curry to the hamster.

The core feeling is “this action is not okay.” It can sound very strong if used directly to someone, so in real life, Japanese speakers sometimes soften it with words like ちょっと (chotto) or by changing the tone. But the basic grammar remains the same.

Structure / Formation

Basic Pattern

The base formula of this grammar point is:

• V-て + は + いけない

You always attach ～てはいけない to the V-て form of a verb.

In shorthand:

• V-て + は + いけない
• V-て + は + いけません (polite)

Here, いけない (ikenai) literally has the idea of “not good / not acceptable.” So, for example, 食べてはいけない (tabete wa ikenai) is like saying “(It is) not acceptable to eat,” or simply, “You must not eat.”

How to Make the V-て Form

To use ～てはいけない, you first need to change the verb into its V-て form. Here are some common patterns for JLPT N5 verbs.

Verb Type	V-る (dictionary)	V-て form	Meaning
る-verb	食べる taberu	食べて tabete	to eat
る-verb	見る miru	見て mite	to see, to watch
う-verb (ending in う, つ, る)	会う au	会って atte	to meet
う-verb (ending in ぶ, む, ぬ)	遊ぶ asobu	遊んで asonde	to play, hang out
う-verb (ending in く)	書く kaku	書いて kaite	to write
う-verb (ending in ぐ)	泳ぐ oyogu	泳いで oyoide	to swim
う-verb (ending in す)	話す hanasu	話して hanashite	to speak
Irregular	する suru	して shite	to do
Irregular	来る kuru	来て kite	to come

Once you have the V-て form, just add は and いけない / いけません.

Putting It Together

Here is the full pattern again:

• V-て + は + いけない (plain) – must not (casual / neutral)
• V-て + は + いけません (polite) – must not (polite)

Some simple examples with a bit of a twist:

Plain form (いけない)

• テストで宇宙人に答えを聞いてはいけない。
• Tesuto de uchūjin ni kotae o kiite wa ikenai.
• You must not ask aliens for the answers on the test.

Polite form (いけません)

• 図書館でロボットを踊らせてはいけません。
• Toshokan de robotto o odorasete wa ikemasen.
• You must not make your robot dance in the library.

Spoken Shortcut: ～ちゃいけない

In casual spoken Japanese, は is often shortened and slurred. You will hear:

• V-て + は + いけない → V-ちゃいけない

For example:

• ここでドラゴンを呼んじゃいけないよ。
• Koko de doragon o yobja ikenai yo.
• You must not summon a dragon here.

For now, as a beginner, it is safer to use the full form ～てはいけない yourself. Just remember that ～ちゃいけない is the same grammar in very casual speech, so you can recognize it when you hear it.

Nuance and Usage Tips

Some helpful points to use ～てはいけない naturally:

• It sounds like a rule or strong warning. Saying it directly to someone can feel strict, like a teacher or parent talking, depending on the tone.
• The polite form ～てはいけません is common on signs and in public announcements.
• It can also be used when talking about yourself, to remind yourself of rules:
  • 朝にゲームをしすぎてはいけない。
  • Asa ni gēmu o shisugite wa ikenai.
  • I must not play games too much in the morning.

As you read Japanese at N5 level, whenever you see a verb in V-て form followed by はいけない or はいけません, you can safely think: “This action is not allowed.”

Example Sentences

• ここでタイムマシンを使ってはいけません。
• Koko de taimu mashin o tsukatte wa ikemasen.
• You must not use a time machine here.

• テストの前にカンニングしたらいけないよ。
• Tesuto no mae ni kanningu shitara ikenai yo.
• You must not cheat before the test.

• 宇宙船の中でボールを投げてはいけない。
• Uchūsen no naka de bōru o nagete wa ikenai.
• You must not throw a ball inside the spaceship.

• おばあちゃんのスマホを勝手にさわってはいけません。
• Obāchan no sumaho o katte ni sawatte wa ikemasen.
• You must not touch Grandma’s smartphone without permission.

• 天才ねこに宿題をやらせてはいけないと思います。
• Tensai neko ni shukudai o yarasete wa ikenai to omoimasu.
• I think you must not make the genius cat do your homework.

Quick Practice

(Answers and explanations are right under this section.)

Multiple-Choice

1. Choose the correct polite sentence: “You must not sleep in the classroom.”

• A. 教室で寝てはいけません。(Kyoushitsu de nete wa ikemasen.)
• B. 教室で寝てはでもいけません。(Kyoushitsu de nete wa demo ikemasen.)
• C. 教室で寝てはといけません。(Kyoushitsu de nete wa to ikemasen.)
• D. 教室で寝てやいけません。(Kyoushitsu de nete ya ikemasen.)

2. Choose the correct casual sentence using ～てはいけない: “You must not open this magic door.”

• A. このまほうのドアを開けてはいけない。(Kono mahou no doa o akete wa ikenai.)
• B. このまほうのドアを開けてはやいけない。(Kono mahou no doa o akete wa ya ikenai.)
• C. このまほうのドアを開けてといけない。(Kono mahou no doa o akete to ikenai.)
• D. このまほうのドアを開けてなどいけない。(Kono mahou no doa o akete nado ikenai.)

3. Choose the correct sentence that uses the casual spoken form ～ちゃいけない.

• A. 公園でドラゴンを走っちゃいけないよ。(Kouen de doragon o hasoccha ikenai yo.)
• B. 公園でドラゴンを走ってはいけませんよ。(Kouen de doragon o hashitte wa ikemasen yo.)
• C. 公園でドラゴンを走らせちゃいけないよ。(Kouen de doragon o hasirasete cha ikenai yo.)
• D. 公園でドラゴンを走らせてちゃいけないよ。(Kouen de doragon o hasirasete cha ikenai yo.)

4. Choose the correct negative rule sentence: “At this library, you must not eat snacks.”

• A. この図書館ではおかしを食べてはいけません。(Kono toshokan de wa okashi o tabete wa ikemasen.)
• B. この図書館ではおかしを食べませんてはいけません。(Kono toshokan de wa okashi o tabemasen te wa ikemasen.)
• C. この図書館ではおかしを食べたてはいけません。(Kono toshokan de wa okashi o tabetate wa ikemasen.)
• D. この図書館ではおかしを食べるといけません。(Kono toshokan de wa okashi o taberu to ikemasen.)

5. Choose the sentence that correctly says “We must not forget Grandma’s birthday.”

• A. おばあちゃんのたん生日をわすれてはといけません。(Obaachan no tanjoubi o wasurete wa to ikemasen.)
• B. おばあちゃんのたん生日をわすれてはいけません。(Obaachan no tanjoubi o wasurete wa ikemasen.)
• C. おばあちゃんのたん生日をわすれないではいけません。(Obaachan no tanjoubi o wasurenai de wa ikemasen.)
• D. おばあちゃんのたん生日をわすれてやいけません。(Obaachan no tanjoubi o wasurete ya ikemasen.)

Spot-the-Error

6. One of the following sentences has a mistake with ～てはいけない. Which one is incorrect?

• A. 夜にロボットとあまりさわいではいけません。(Yoru ni robotto to amari sawaide wa ikemasen.)
• B. 博物館で写真をとってはいけません。(Hakubutsukan de shashin o totte wa ikemasen.)
• C. テストのとき、スマホを見てはいけません。(Tesuto no toki, sumaho o mite wa ikemasen.)

7. One of the following sentences has a mistake with the form before ～てはいけない. Which one is incorrect?

• A. 学校で先生のロボットをこわしてはいけない。(Gakkou de sensei no robotto o kowashite wa ikenai.)
• B. プールでサメにさわっいてはいけません。(Puuru de same ni sawaitte wa ikemasen.)
• C. 電車の中で大きい声で歌ってはいけません。(Densha no naka de ookii koe de utatte wa ikemasen.)

Translation

8. Translate into Japanese using ～てはいけない: “You must not tell this secret to the goldfish.”

9. Translate into Japanese using the polite form ～てはいけません: “In this park, you must not fly a UFO.”

10. Translate into Japanese using the casual spoken form ～ちゃいけない: “You must not eat my cake.”

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Answers and Explanations

1. 教室で寝てはいけません。(Kyoushitsu de nete wa ikemasen.) – This is the correct polite pattern V-て＋は＋いけません with the meaning “must not sleep.”
2. このまほうのドアを開けてはいけない。(Kono mahou no doa o akete wa ikenai.) – This uses the standard casual form ～てはいけない correctly after the V-て form 開けて.
3. 公園でドラゴンを走らせちゃいけないよ。(Kouen de doragon o hasirasete cha ikenai yo.) – This correctly uses the contracted spoken form ～ちゃいけない after 走らせて → 走らせちゃ.
4. この図書館ではおかしを食べてはいけません。(Kono toshokan de wa okashi o tabete wa ikemasen.) – This is the correct polite prohibition with V-て＋は＋いけません to state a rule.
5. おばあちゃんのたん生日をわすれてはいけません。(Obaachan no tanjoubi o wasurete wa ikemasen.) – The verb わすれる is in て-form わすれて, then followed by はいけません for “must not forget.”
6. 夜にロボットとあまりさわいではいけません。(Yoru ni robotto to amari sawaide wa ikemasen.) – The error is the extra で after さわい; it should be さわいではいけません using the て-form さわいで＋は＋いけません.
7. プールでサメにさわっいてはいけません。(Puuru de same ni sawaitte wa ikemasen.) – The mistake is the wrong て-form さわっいて; the correct て-form is さわって, so it should be さわってはいけません.
8. このひみつを金魚に言ってはいけない。(Kono himitsu o kingyo ni itte wa ikenai.) – 言う becomes 言って in て-form, then plus はいけない for “must not tell.”
9. この公園ではUFOを飛ばしてはいけません。(Kono kouen de wa yūfō o tobashite wa ikemasen.) – The polite prohibition uses 飛ばして (て-form of 飛ばす) with ～てはいけません.
10. 私のケーキを食べちゃいけない。(Watashi no kēki o tabecha ikenai.) – 食べて＋はいけない becomes the spoken contraction 食べちゃいけない for a casual “must not eat.”