How to tell them apart
な attaches directly to a verb and delivers a blunt, informal command not to do something, typically from a male speaker in casual speech. てはいけない uses the て-form plus てはいけない and expresses a rule or prohibition that applies regardless of who is speaking, often in formal contexts. Swapping them feels wrong because な is too rough for posted rules like 部屋に入ってはいけない, while てはいけない is too stiff for a direct personal order like 行くな！.
- な Use な when giving a blunt, informal command to someone not to do something, typically as a male speaker.
- はいけない Use てはいけない when stating a rule or prohibition that something must not be done, in formal or neutral contexts.
| Grammar point | Meaning | JLPT level |
|---|---|---|
| な na | A command form telling someone not to do something | N5 |
| はいけない haikenai | Not allowed; must not do | N4 |
な na
A command form telling someone not to do something
な turns a verb into a blunt negative command, telling someone not to do the action. It follows the dictionary form of the verb directly, as in 行くな or 食べるな. The tone is strong and direct, so it is mostly used in casual speech or when speaking down to someone.
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あなたからさまざまなことを学びました。
I learned a lot from you.
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あなたって、なんてきれいなんでしょう！
How beautiful you are!
はいけない haikenai
Not allowed; must not do
はいけない follows the te-form of a verb and states that the action is forbidden or should not be done, as in 読んではいけない. With a negative te-form, なくてはいけない instead expresses that something must be done. It is used in both plain and polite contexts.
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母は昼食後すぐに運動しすぎてはいけないと言う。
My mother disapproves of too much exercise right after lunch.
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問題をこのままにしておいてはいけない。
We shouldn't let the problem rest here.
な and はいけない are JLPT N5–N4 grammar points that Japanese learners often mix up. This page compares them side by side on meanings, usage and example sentences, so you can tell them apart.