てはいけない (te wa ikenai) Meaning Japanese Grammar - Must Not

Author Sandro Maglione for article 'てはいけない (te wa ikenai) Meaning Japanese Grammar - Must Not'

Sandro Maglione

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てはいけない (te wa ikenai) Meaning Japanese Grammar - Must Not

The expression てはいけない (tewaikenai) means must not. It is one of the grammatical forms in Japanese that are used to state something you must not do.

Other grammatical forms that indicate must not or should not are:

In this post we are going to learn more about the meaning of てはいけない, how it is formed, and when てはいけない is used through real example sentences.

How てはいけない is formed

てはいけない is composed by:

  • て form of the preceding verb (which is the action that must not be done)
  • Particle は (wa), which indicates the topic
  • いけない: Potential form (られる) of the verb ()く (to go)

For this reason, the literal translation of てはいけない is:

てはいけない: Not being able to go



You must not enter there.

How and when to use てはいけない

てはいけない is the most common expression for stating an action that must not be done.

てはいけない can be translated as must not, should not, or even it would be better not to, depending on the context of the sentence.


You must not make noise here。

Let's break this sentence down to understand its meaning:

  • ここ: means this, and is part of the Kosoado series
  • : Particle used to indicate the place where an action is performed (swimming in the pond)
  • (さわ)いではいけない: Form of てはいけない
    • (さわ)いで: The verb (さわ)ぐ means to make noise, and in this sentence we use its て form (changing ぐ to いで)
    • : Particle indicating the topic
    • いけない: Potential form of the verb ()

It is also possible to find ては in its more colloquial form ちゃ or じゃ instead of では:


You mustn’t play outside.

ちゃ and じゃ are more common in spoken language as they are easier and faster to pronounce.

てはいけません - Polite form of てはいけない

To make the sentence more formal, you can use the polite form of ない: ません; the expressione becomes てはいけません.



You must not swim in this pond.

だめだ, いけない, and ならない

だめだ (dameda), てはいけない (tehikenai), and てはならない (tehanaranai) are three expressions that all mean must not.

The main difference between these three forms is the degree of formality and prohibition:

  • てはいけない: most common expression, used both in written and spoken language
  • てはならない: more formal and direct version of てはいけない, used more often in written language
  • だめだ: more colloquial expression, used almost exclusively in spoken language

The meaning of ()かない is to not go, while the meaning of ()けない is cannot go.

Examples of てはいけない


Do not watch TV.

Cover of the book 'terebi o mitewa ikenai'
Publication by Dr. Tomabeichi Hideto, expert in Cognitive Science, Neuroscience, scientific researcher on the influence of mass media on the human brain.


You must not sleep during the lesson.


Don't forget to practice.