Must not / Should not – Casual prohibition expressions
JLPT N5 文法 ～ちゃいけない / ～じゃいけない 解説
Master ～ちゃいけない / ～じゃいけない in 5 minutes. Learn how to say "must not" in casual Japanese – a must‑know for understanding real conversations and JLPT N5 listening.
🚀 Quick JLPT N5 Warm-up Quiz
Q1: How do you say "You must not eat here" in casual Japanese? A. ここで食べちゃいけない B. ここで食べますいけない
Answer: A (食べちゃ = 食べては → ちゃいけない = must not eat)
Quick Summary
Grammar Point ～ちゃいけない / ～じゃいけない
Meaning Must not / Should not
Formation Verb て-form: ～ては → ～ちゃ ～では → ～じゃ
Example 食べちゃいけない。たべちゃいけない。Tabecha ikenai. Must not eat.
💡 Switch to Hiragana only or Rōmaji if you're just starting out.
What does ～ちゃいけない / ～じゃいけない mean?
This casual grammar pattern means "must not" or "should not" — it expresses strong prohibition. It's the everyday spoken version of the formal ～てはいけません / ～ではいけません.
～ちゃいけない → used after て-form verbs that end in て (e.g., 食べて → 食べちゃ).
～じゃいけない → used after て-form verbs that end in で (e.g., 飲んで → 飲んじゃ).
友達との会話でよく使います。ともだちとのかいわでよくつかいます。Tomodachi to no kaiwa de yoku tsukaimasu.
The formal version uses ～てはいけません / ～ではいけません, but on the JLPT N5, the casual forms often appear in listening sections.
How to Pronounce
～ちゃいけない： cha i ke na i
～じゃいけない： ja i ke na i
食べちゃいけない / 飲んじゃいけない / 行っちゃいけない
Examples & Mini Dialogue
食べちゃいけない。たべちゃいけない。Tabecha ikenai.
Must not eat it. (Verb: 食べる → 食べて → 食べちゃ)
食べては → 食べちゃ. The ては contracts to ちゃ.
飲んじゃいけない。のんじゃいけない。Nonja ikenai.
Must not drink it. (Verb: 飲む → 飲んで → 飲んじゃ)
飲んでは → 飲んじゃ. The では contracts to じゃ.
行っちゃいけない。いっちゃいけない。Itcha ikenai.
Must not go. (Verb: 行く → 行って → 行っちゃ)
行っては → 行っちゃ. Note the small っ.
🗣️ Mini Dialogue
A: 写真を撮ってもいい？しゃしんをとってもいい？Shashin o totte mo ii?
B: ダメ、撮っちゃいけない。だめ、とっちゃいけない。Dame, totcha ikenai.
("Can I take a photo?" — "No, you mustn't.")
When to Use in Real Japan
With close friends:言っちゃいけないいっちゃいけないitcha ikenai (Don't say that)
Parents to children:触っちゃいけないさわっちゃいけないsawatcha ikenai (Don't touch)
Rules in casual settings:入っちゃいけないはいっちゃいけないhaiccha ikenai (No entry)
⚡ Casual (ちゃ/じゃ) vs Formal (ては/では) – When to Use Which
The JLPT N5 may test your ability to recognize both forms. The informal contraction is extremely common in spoken Japanese.
Formality
Pattern
Example
Casual
～ちゃいけない / ～じゃいけない
食べちゃいけない
Formal
～てはいけません / ～ではいけません
食べてはいけません
💡 Exam tip: If you hear ちゃ/じゃ in the listening section, it's the casual prohibition. The formal version ends with いけません.
Common Mistakes
✕食べじゃいけないたべじゃいけないTabe ja ikenai
✓食べちゃいけないたべちゃいけないTabecha ikenai
(食べて → 食べちゃ, not 食べじゃ)
🔍 Why? The contraction depends on the て-form ending: て becomes ちゃ; で becomes じゃ.
✕飲むちゃいけないのむちゃいけないNomu cha ikenai
✓飲んじゃいけないのんじゃいけないNonja ikenai
(Must first make て-form: 飲んで → 飲んじゃ)
🔍 Always start from the て-form, then apply the contraction rule.
🎌 JLPT N5 Exam Trick
In the listening section, you might see a sign or hear a phrase like:
ここで遊んじゃいけない
Don't be thrown off by the casual ending. Just remember: ちゃ/じゃ + いけない = prohibition. The formal equivalent would be ～てはいけません.
JLPT N5 Practice Questions
1. Which is the casual prohibition of "must not write" (書く)?
A. 書いちゃいけない
B. 書くちゃいけない
Show AnswerCorrect: A (書いて → 書いちゃ)
2. "Must not drink" (飲む) in casual form:
A. 飲むじゃいけない
B. 飲んじゃいけない
Show AnswerCorrect: B (飲んで → 飲んじゃ)
3. What is the formal equivalent of 入っちゃいけない?
A. 入ってはいけません
B. 入りはいけません
Show AnswerCorrect: A (入って + はいけません)
⚠️ N5 listening often uses casual speech — don't get confused on test day.
This lesson is taught by Anup Sensei, an experienced Japanese language instructor at Gogaku Language & Training Center in Pokhara. He has studied and worked in Japan and specializes in practical JLPT preparation and real-life communication skills.
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