ちゃいけない・じゃいけない: must not do

ちゃいけない・じゃいけない means must not do. It is a JLPT N5 Japanese grammar pattern used to tell someone that an action is prohibited.

This grammar point appears often in beginner conversations, textbooks, and JLPT-style reading questions. If you want to say that something is not allowed in casual Japanese, ちゃいけない・じゃいけない is a useful pattern to learn early because it connects directly to everyday communication.

What does ちゃいけない・じゃいけない mean?

Use ちゃいけない・じゃいけない when you want to say that an action is against a rule, request, or expectation.

Natural translations include:

• must not
• should not
• it is not okay to

The exact English translation changes with context. The important point is to understand what job the pattern is doing in the sentence, not to memorize only one English phrase.

How to form ちゃいけない・じゃいけない

Verb て-form without て + ちゃいけない / Verb で-form without で + じゃいけない

Examples of the pattern:

• 食べてはいけない → 食べちゃいけない
• 飲んではいけない → 飲んじゃいけない
• 見てはいけない → 見ちゃいけない

Pay attention to the form that comes before the grammar point. Many beginner mistakes happen because the learner understands the meaning but attaches the pattern to the wrong word form.

When is ちゃいけない・じゃいけない used?

Use ちゃいけない・じゃいけない in situations like:

• giving casual warnings
• explaining rules to friends or children
• saying what someone should avoid

Tone and register:

• casual and spoken; use てはいけません for formal rules
• Common in daily speech, textbook examples, and beginner JLPT questions

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 must not take pictures here.
• まだそれを食べちゃいけないよ。 — You should not eat that yet.
• この部屋に入っちゃいけない。 — You must not enter this room.
• 授業中にスマホを使っちゃいけない。 — You must not use your phone during class.
• お酒を飲んじゃいけない日は運転しない。 — On days when you must not drink alcohol, do not drive.

Read the Japanese sentence first, then check whether the English translation matches the feeling of the whole sentence. This helps you avoid translating each piece too literally.

Nuance of ちゃいけない・じゃいけない

The key nuance is a casual spoken prohibition.

This matters because learners often know the dictionary meaning but miss the speaker’s intention. In real Japanese, grammar points show attitude, politeness, contrast, certainty, desire, or context. For ちゃいけない・じゃいけない, focus on how the pattern changes the role of the sentence.

For example:

• In conversation, it can sound direct but familiar, especially with people you know.
• Compared with てはいけない, it feels more casual and compressed.

ちゃいけない・じゃいけない vs てはいけない

Both ちゃいけない・じゃいけない and てはいけない can be related in beginner Japanese, but they are different.

ちゃいけない・じゃいけない:

• spoken contraction of てはいけない / ではいけない
• sounds natural in casual warnings

てはいけない:

• more complete and more formal
• better for signs, school rules, and polite explanations

Quick contrast examples:

• ここで走っちゃいけない。— Do not run here.
• ここで走ってはいけません。— Running here is not allowed.

If you are unsure which one to use, ask what the sentence is trying to do: define something, ask something, show a reason, mark a subject, describe a desire, or connect ideas.

Common mistakes with ちゃいけない・じゃいけない

Watch out for these mistakes:

• Using ちゃ with verbs that require じゃ after the んで form
• Using it in very formal writing when てはいけません is better
• Confusing prohibition with necessity, such as なければならない

A good study habit is to make one simple original sentence, then change only one part of it. That makes the function of the grammar point easier to see.

Is ちゃいけない・じゃいけない on the JLPT?

Yes. ちゃいけない・じゃいけない is commonly taught as JLPT N5 grammar.

That means learners should be able to:

• recognize it in reading
• understand its nuance in context
• use it in simple original sentences

For test preparation, do not only memorize the English gloss. Practice identifying the word before and after the grammar point, because JLPT questions often test structure and context together.

Practice questions for ちゃいけない・じゃいけない

Try making your own sentences with these prompts:

• Say that you must not eat in the library.
• Tell a friend they should not forget their passport.
• Write one school rule using ちゃいけない.

Keep the sentences short at first. Once the form feels natural, add time words, places, reasons, or contrast to make the sentence more realistic.

Learn ちゃいけない・じゃいけない with Kanjiru

If you want to review ちゃいけない・じゃいけない together with kanji, vocabulary, and other JLPT N5 patterns, Kanjiru helps you practice Japanese in short, focused sessions.

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