Grammar Info

N5 Lesson 9: 7/13


Must not, May not


Verb[て]+ は + いけない


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About てはいけない

てはいけない is used in Japanese to express that (A) 'cannot', or 'must not' be done. It is the combination of a verb in form, the particle, and the negative potential form of () (to be able to go). In this way, it literally means '(A) cannot/is not able to go'.

Although can be dropped from many phrases and expressions, the in this particular grammar point is usually not. This is because いけない would then become the second action in a sequence of events (the usual function of form). However, to make this more casual, is often changed to ちゃ (ては becomes ちゃ), or じゃ (では becomes じゃ), as this is easier to say.


Apart from いけない; ならない and だめ are also frequently used to get across the same meaning. However, they are used in different situations.

いけない - Fairly neutral. Used in both spoken and written language.

ならない - Fairly formal. Used mostly in written language.

だめ - Very casual. Used almost exclusively in spoken language.




    You must not go in there.


    We must not eat whale.


    You must not go into this building.


    You must not eat candy before dinner.


    You must not swim in this pond.

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てはいけない – Grammar Discussion

Most Recent Replies (18 in total)

  • GrimeyPlopFlop


    If this conjugation uses the verb 行く, why does the polite negative and non-polite negative conjugate as いけない and いけません instead of いかない and いきません like 行く does normally?

  • ResFort


    This construction uses the potential form of 行く (行ける, “can go”), not the dictionary form.
    So when conjugating it into the negative we get いけない/いけません (行ける itself is an ichidan verb).

    The literal translation for Aてはいけない is then something like “doing A cannot go”, which is better interpreted as “must not do A”.

  • GrimeyPlopFlop


    Ah, that makes a a lot of sense, thank you!

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