ちゃいけない・じゃいけない means must not do or you can’t do that. It is the spoken, squeezed-together version of てはいけない: when people say 〜てはいけない quickly, the ては turns into ちゃ and the では turns into じゃ. The meaning is the same prohibition; only the sound and the tone change.
You will hear it constantly from parents, older siblings, teachers talking to small children, and friends warning each other. You will almost never see it on a sign.
ちゃいけない is てはいけない said at the speed of real conversation — same rule, friendlier (or sharper) voice.
Practice this in Hane: Practice ちゃいけない・じゃいけない in short JLPT-style rounds in Hane.
What does ちゃいけない・じゃいけない mean?
〜ちゃいけない tells someone that an action is not allowed. The speaker is either stating a rule (“you can’t swim in this river”) or warning someone in the moment (“don’t eat that yet!”).
Natural English depends on who is talking:
- you can’t ~ / you’re not allowed to ~ — explaining a rule to a friend
- don’t ~! — a quick warning
- you mustn’t ~ — a parent or teacher talking to a child
There are two spellings because there are two kinds of て-form. Verbs whose て-form ends in て get ちゃ; verbs whose て-form ends in で get じゃ. That is the whole difference between ちゃいけない and じゃいけない — you never choose between them by meaning.
How to form ちゃいけない・じゃいけない
Start from the full form 〜てはいけない, then squeeze it:
Some pairs to get the rhythm:
- 食べてはいけない → 食べちゃいけない
- 見てはいけない → 見ちゃいけない
- 撮ってはいけない → 撮っちゃいけない (the small っ stays)
- 飲んではいけない → 飲んじゃいけない
- 読んではいけない → 読んじゃいけない
- 泳いではいけない → 泳いじゃいけない
The で-group is small and easy to spot: verbs ending in む, ぶ, ぬ (飲む → 飲んで, 遊ぶ → 遊んで) plus ぐ (泳ぐ → 泳いで). Everything else takes ちゃ.
The polite version is 〜ちゃいけません, and the even more casual version swaps いけない for だめ: 食べちゃだめ.
When is ちゃいけない・じゃいけない used?
Use it when you are speaking casually and want to say that something is off-limits:
- warning a friend or family member in the moment: “Don’t touch that, it’s hot.”
- explaining a rule casually: telling a friend that phones aren’t allowed in class
- adults talking to children: 走っちゃいけません (no running!) is classic teacher Japanese at a pool
- asking whether something is forbidden: ここで食べちゃいけないの？ (Can’t I eat here?)
Keep it out of writing and out of formal speech. Signs, school handbooks, and your boss use the uncontracted てはいけません. When you talk to a customer or a teacher, a request with ないでください usually sounds better than any form of いけない.
ちゃいけない・じゃいけない example sentences
ここで写真を撮っちゃいけない。
You can't take photos here.
まだ食べちゃいけないよ。みんなを待とう。
Don't eat yet. Let's wait for everyone.
この手紙は読んじゃいけない。
You mustn't read this letter.
この川で泳いじゃいけないよ。
You're not allowed to swim in this river.
プールで走っちゃいけません。
No running at the pool!
授業中にスマホを使っちゃいけない。
You can't use your phone during class.
ここで食べちゃいけないの？
Am I not allowed to eat here?
After the examples: Turn these prohibition sentences into active recall with Hane’s short JLPT-style rounds.
Nuance of ちゃいけない・じゃいけない
Because it is casual, ちゃいけない sounds personal. With the full てはいけない, the speaker points at a rule; with ちゃいけない, the speaker is talking to you, right now. That makes it warmer between friends and sharper when an adult scolds a child. The same words can be caring (まだ食べちゃいけないよ, “not yet, wait for everyone”) or a telling-off, depending on voice.
Sentence-final particles shape it further. Adding よ turns it into friendly advice: 泳いじゃいけないよ. Adding の？ turns it into a genuine question: 食べちゃいけないの？ (“So I can’t eat here?”). Without either, a bare ちゃいけない can sound blunt.
Listen for the ちゃ: ちゃいけない (must not do) and なくちゃ (must do) both contain ちゃ and both come from casual speech. Check what comes before it: a plain て-form means “don't”, a ない-form (食べなくちゃ) means “have to”.
ちゃいけない・じゃいけない vs てはいけない
These are the same grammar point in two registers, so the question is never “what does it mean?” but “where am I?”
If you are writing, choose てはいけない. If you are chatting and the full form feels stiff, contract it. And if you are asking a stranger or a customer not to do something, switch to a request with ないでください instead of either.
Common mistakes with ちゃいけない・じゃいけない
The て-form of 飲む is 飲んで, with で. で becomes じゃ, not ちゃ.
起きちゃいけない means “you must not get up.” To say you have to do something, use the ない-form: なくちゃ.
Contractions belong in speech. Written notices and rules use the full てはいけません.
Is ちゃいけない・じゃいけない on the JLPT?
Yes. The prohibition てはいけない is core N5 grammar, and its contracted form ちゃいけない・じゃいけない shows up mainly in the listening section, where speakers talk naturally.
- Hear 撮っちゃいけない and understand it as 撮ってはいけない
- Tell ちゃいけない (don't) apart from なくちゃ (have to) by the verb form in front
- Know that じゃ appears after で-type verbs such as 飲んで and 泳いで
In a listening question, a mother or teacher often says something like 「そこで遊んじゃいけませんよ」 and you have to pick what the child must not do. The trap answer usually shows the opposite action, so decide whether you heard a prohibition or an obligation before looking at the pictures.
Practice questions for ちゃいけない・じゃいけない
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図書館で食べちゃいけないよ。 — You can't eat in the library.
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遊んじゃいけない。 — You mustn't play.
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窓を開けちゃいけないよ。 — Don't open the window.
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ここで写真を撮っちゃいけないの？ — Am I not allowed to take photos here?
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読んじゃいけない。 — You mustn't read it. (読んで ends in で, so it becomes じゃ.)
Learning path for ちゃいけない・じゃいけない
Related grammar to review next
- てはいけない — the uncontracted form; use it in writing and polite speech.
- なくちゃ — the casual “have to”; it sounds similar but means the opposite.
- てもいいです — the permission question that ちゃいけない often answers.
- ないでください — the polite request to use instead of a prohibition with strangers.
- ちゃう — the N4 contraction built on the same ちゃ/じゃ sound change.
Learn ちゃいけない・じゃいけない with Hane
Hane drills ちゃいけない side by side with てはいけない and なくちゃ, so you learn to hear the difference at conversation speed. Try Hane and keep going with the N5 grammar lessons.
FAQ about ちゃいけない・じゃいけない
What does ちゃいけない・じゃいけない (cha ikenai ja ikenai) mean in Japanese?
ちゃいけない・じゃいけない (cha ikenai ja ikenai) means “must not do”. It is JLPT N5 grammar. 〜ちゃいけない tells someone that an action is not allowed. The speaker is either stating a rule (“you can't swim in this river”) or warning someone in the moment (“don't eat that yet!”).
How do you form ちゃいけない・じゃいけない (cha ikenai ja ikenai)?
Start from the full form 〜てはいけない, then squeeze it: 食べては→ちゃ+いけない 飲んでは→じゃ+いけない て-form ending in て: drop て, add ちゃいけない · て-form ending in で: drop で, add じゃいけない Some pairs to get the rhythm: - 食べてはいけない → 食べちゃいけない - 見てはいけない → 見ちゃいけない - 撮ってはいけない → 撮っちゃいけない (the…
What is the difference between ちゃいけない・じゃいけない and てはいけない?
ちゃいけない・じゃいけない: spoken, casual. てはいけない: full form, neutral to formal.
What is an example sentence with ちゃいけない・じゃいけない (cha ikenai ja ikenai)?
ここで写真を撮っちゃいけない。 — You can't take photos here.