How to say Must not do and Cannot continue to do in Japanese

1. Introduce about 「てはいけない」and 「てはいられない」

✅ Similarities:

Both structures include 「ては」 and are somewhat related to restrictions or inability to continue an action.

✅ Main Differences:

Expression	Meaning & Nuance	Usage
「てはいけない」	“Must not do A” (Prohibition, restriction, rules)	Used to express rules, moral constraints, or prohibitions
「てはいられない」	“Cannot continue A” (Due to urgency or necessity)	Used to express that one cannot continue an action due to external circumstances or personal determination

2.「てはいけない」: Prohibition

✅ Structure:

Vて + はいけない

✅ Meaning:

Indicates prohibition or restriction, meaning “must not do A”.

Stronger than “だめ” (dame) and more formal.

Used in laws, rules, commands, and societal regulations.

✅ 📌 Example Sentences:

「ここでタバコを吸ってはいけません。」
(You must not smoke here.)
→ (A rule or restriction.)

「夜遅くまでゲームをしてはいけません。」
(You must not play games until late at night.)
→ (A parental rule or restriction.)

「授業中に携帯を使ってはいけない。」
(You must not use your phone during class.)
→ (A school rule or disciplinary measure.)

✅ 📌 Usage Contexts:

Laws & Regulations: 「車は赤信号で進んではいけません。」(You must not proceed when the traffic light is red.)

Social Norms: 「他人のものを勝手に使ってはいけない。」(You must not use other people’s belongings without permission.)

School & Work Rules: 「仕事中に私用電話をかけてはいけません。」(You must not make personal calls during work.)

3.「てはいられない」: Inability to Continue an Action

✅ Structure:

Vて + はいられない

✅ Meaning:

Indicates that one “cannot afford to continue doing A”.

Can be used for both external situations (time constraints, urgency) and personal will (determination).

Emphasizes that continuing the action is no longer possible.

✅ 📌 Example Sentences:

「のんびりしてはいられない。」
(I can’t afford to be relaxed.)
→ (The situation demands action.)

「もう待ってはいられない。」
(I can’t wait any longer!)
→ (Indicates frustration or urgency.)

「試験が近いので、遊んではいられない。」
(The exam is approaching, so I can’t keep playing.)
→ (Indicates necessity to focus on studies.)

✅ 📌 Usage Contexts:

Urgent Situations: 「こんな状況では安心してはいられない。」(In this situation, I can’t afford to feel at ease.)

Time Constraints: 「時間がないので、ゆっくりしてはいられない。」(There’s no time, so I can’t take it easy.)

Personal Determination: 「いつまでも親に頼ってはいられない。」(I can’t keep relying on my parents forever.)

4. Can “てはいけない” and “てはいられない” Be Used Interchangeably?

✅ They CANNOT be directly interchanged because their functions are entirely different:

Sentence	Can It Be Replaced?	Reason
「ここでタバコを吸ってはいけません。」	❌ 「ここでタバコを吸ってはいられません。」	“てはいけない” means prohibition, while “てはいられない” would mean “I can’t resist smoking,” which changes the meaning.
「試験が近いので、遊んではいられない。」	❌ 「試験が近いので、遊んではいけない。」	“てはいられない” expresses subjective urgency, while “てはいけない” would mean a strict rule against playing.
「こんな状況では安心してはいられない。」	❌ 「こんな状況では安心してはいけない。」	“てはいられない” means “I can’t stay relaxed,” while “てはいけない” would mean “it is forbidden to be relaxed,” which is unnatural.

📌 Summary:

「てはいけない」 = External prohibition (rules, laws, instructions).

「てはいられない」 = Subjective inability to continue (urgency, pressure, determination).

5. Which One Appears More in JLPT N2/N3?

✅ 「てはいけない」 → N4 / N3 Grammar (Basic Rules & Prohibition)

Common in N4/N3 exams, mainly in grammar and reading comprehension.

Used in daily life, school rules, company policies, and general prohibitions.

✅ 「てはいられない」 → N2 Grammar (More Advanced Usage)

Common in N2 exams, especially in reading comprehension and writing.

Frequently appears in scenarios involving urgency, time constraints, and personal decisions.

Often tested alongside「〜ていられない」「〜ていられなくなる」.

📌 JLPT Exam Frequency

Grammar	JLPT Level	Exam Frequency
「てはいけない」	N3 / N4	🌟🌟🌟🌟🌟（Very High）
「てはいられない」	N2	🌟🌟🌟🌟（High）

6. Summary

Grammar	Meaning	Usage	JLPT Level
「てはいけない」	“Must not do” (Prohibition)	Rules, laws, instructions	N3 / N4
「てはいられない」	“Cannot continue A” (Urgency, necessity)	Time constraints, determination	N2

💡 How to Choose? ✅ If it’s about prohibition, rules, or restrictions → Use「てはいけない」
✅ If it’s about not being able to continue an action due to circumstances or determination → Use「てはいられない」

7. 🎯 Practice Questions

「明日は試験があるので、今日は遊ん＿＿＿＿＿＿。」
(Tomorrow is the exam, so I can’t keep playing today.)
- A. てはいられない
- B. てはいけない
- ✅ Correct Answer: A (indicating “I can’t keep playing” due to urgency.)

「学校のルールでは、教室でスマホを使っ＿＿＿＿＿＿。」
(According to school rules, you must not use a smartphone in the classroom.)
- A. てはいられない
- B. てはいけない
- ✅ Correct Answer: B (expressing a strict rule.)