Japanese Grammar

Prohibition: 〜てはいけない / 〜てはいけません

To say 'You must not' or 'It is forbidden to', Japanese uses the ~te wa ikenai form. This is how rules, warnings, and prohibitions are expressed.

How to say 'You must not'

While ~te mo ii means 'It's okay to do X', the opposite is ~te wa ikenai / ~te wa ikemasen, which means 'It's NOT okay / You must NOT do X'.

This is the standard form used for rules (No photography!), parental warnings (Don't do that!), and official prohibitions.

The casual form is ~te wa dame (da/desu), which is softer and used in everyday speech. The more formal/literary form is ~te wa naranai.

Conjugation Rules

Making the Prohibition Form
Te-form
→Te-form + はいけません (wa ikemasen)
It is not allowed to...
食べる -> 食べて
→食べてはいけません。
You must not eat.
入る -> 入って
→入ってはいけません。
You must not enter.
Casual vs Polite vs Formal
Casual
→〜てはだめ (te wa dame)
No! / Don't! (said by parents to children)
Polite
→〜てはいけません (te wa ikemasen)
You must not... (standard)
Formal / Written
→〜てはならない (te wa naranai)
One must not... (legal, very formal)

Example Sentences

ここでタバコを吸ってはいけません。
Koko de tabako o sutte wa ikemasen.
You must not smoke here.
嘘をついてはだめだよ。
Uso o tsuite wa dame da yo.
You must not tell lies. (Casual, parental tone)
法律を破ってはならない。
Houritsu o yabutta wa naranai.
One must not break the law. (Formal/Written)

Teacher's Advice

Permission vs Prohibition

A very common exam trap is mixing up ~te mo ii (OK to do) and ~te wa ikemasen (must NOT do). Remember the key: 'mo ii' has the positive word 'ii' (good/okay). 'wa ikemasen' literally means 'does not go well' → NOT okay.

JLPT Exam Patterns

  • •Choosing between ~te mo ii (allowed) and ~te wa ikemasen (forbidden) (N5)
  • •Reading signs and rules using this grammar (N5)
  • •Understanding ~te wa naranai in written/formal texts (N4)

Know the Rules

Practice making sentences about what you must not do using real-life scenarios.

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