Two types of “can’t” in Japanese: improper vs impossible

By | January 29, 2018

When learning a foreign language, often it is good to try and get away from your native language and think in the foreign language so you don’t end up saying things that sounds like they came out of a translation program. Having said that, when speaking that foreign language it will take time for your native-language thinking to go away, so sometimes it can be insightful to look at a foreign language through the lens of your own.

In this post I’d like to talk about how the idea of “can’t” can be represented in Japanese to mean two very different things. The trick here is that (though you may not be consciously aware of it), the word “can’t” can be used to describe two concepts. Let’s compare these sentences:

  • You can’t run that toy without a battery.
  • You can’t smoke in here.

Can you see the difference?

The first is expressing that using the toy without a battery is impossible, the second says that it is improper (or impolite) to smoke somewhere. For the second case, you can replace the word “shouldn’t” with “can’t” to clarify the meaning, but you can’t do that with the first.

The reason having an active understanding of this difference is important is because in Japanese these two ideas are expressed with very different grammar.


There word ‘impossible’ can be expressed in a few ways in Japanese, for instance:

  • 無理 (muri)
  • 不可能 (fukanou)
  • ありえない (arienai)

The first of these (無理) is more informal and more conversational, the second (不可能) sounds more scientific and technical.

Anyway, there are two common ways to express something being impossible in Japanese. The first is to use the negative form of the verb できる (dekiru, “to be able to”), which is できない (dekinai) in the following patterns:

  • noun + できない
  • dictionary-form verb + ことができない

For example:

  • 僕は運転できない (boku ha unten dekinai)
    • I can’t drive
  • 僕はフランス語を話すことができない (boku ha fransugo wo hanasu koto ga dekinai)
    • I can’t speak French.

(Note: for polite-form Japanese you would use 出来ません (dekimasen) instead)

The second common way to express impossibility is with the negative of the potential form. So for example, with the word 話す (hanasu), the potential would be 話せる (hanaseru) and the negative potential 話せない (hanasenai):

  • 僕は日本語を話せない  (boku ha nihongo wo hanasenai)
  • I can’t speak Japanese.

This form is the shortest and the best for casual conversation, in my opinion. The disadvantage of this form for beginning students is you have to learn the conjugation of the potential form (you can see a convenient table midway down this page). Also, if you are using a verb that only works in combination in する (like 勉強する), you end up using できない anyway since できない is the negative potential form of する.

By the way, another way to state the impossible is by using words I listed above (無理・不可能・ありえない). The pattern is:

  • dictionary-form verb + のは +  無理 or 不可能 or ありえない

For example:

  • フランス語を話すのは無理。  (furansugo wo hanasu no ha muri)
  • French is impossible to speak.

Keep in mind that just like the above English translation, this form sounds a little stiff so I generally would stick to other two alternatives I mentioned (できない or the negative potential form).


Japanese has several commonly used patterns to express something is improper. Here is a summary of the most common ones:

  • te-form verb + は + だめ     (polite form: 〜だめです)
  • te-form verb + は + いけない  (polite form: 〜いけません)
  • te-form verb + は + ならない  (polite form: 〜なりません)

The first of these (だめ)is the most informal, the second (いけない) is a bit more formal, and the third (ならない) sounds a bit classic to me, though it is still used.

Here is examples of each in the non-polite forms. I’ll use the same verb (走る, hashiru, “to run”) to make it easy to follow:

  • 走ってはだめ (hashitte ha dame)
  • 走ってはいけない  (hashitte ha ikenai)
  • 走ってはならない  (hashitte ha naranai)
  • It’s is not proper to run (here)

Even in the non-polite form, the above Japanese sentences sound a little stiff because the ては (te ha) combination is commonly contracted to ちゃ (cha) in this context (see my list of abbreviations here). So these would become:

  • 走っちゃだめ (hashiccha dame)
  • 走っちゃいけない  (hashiccha ikenai)
  • 走っちゃならない  (hashiccha naranai)

I have occasionally heard the word 悪い (warui, “bad”) instead of だめ to mean the same thing, though I wouldn’t recommending using that. (Ex: 走っちゃ悪い)


I hope this article was a good review of the two different ways of expressing “can’t” in Japanese.

I didn’t focus on it in this article, but you can make a similar distinction for the word “can”. For example:

  • I can speak English.   (possibility)
    • 僕は英語を話せる   (boku ha eigo wo hanaseru)
  • You can go home. (permission)
    • 帰っていいよ  (kaette ii yo)

Note that for the “permission” case, not only to you use いい (“ii”, good) instead of a word like だめ, but you don’t use the particle は after the te-form of the verb, unlike the “improper” case where you do.

Once you get used to thinking in Japanese, this distinction will come naturally. But for students that are just learning these  forms (and once in awhile maybe for experienced learners too), you may have to stop and think whether you are trying to express improper or impossible.


Translate the following sentences into Japanese, being careful to think about how “can’t” is used.

  1. You can’t walk 1000 miles.
  2. You can’t interfere.
  3. You can’t dance in those shoes.


Note: there are several right answers, but I’ll just give a few for each.

  1. 1000マイルは歩けない  (also  1000マイルは歩くことができない)
  2. 邪魔しちゃだめ。  (also  邪魔してはだめ  or  邪魔ちゃいけない   etc…)
  3. その靴で踊れない   (or  その靴で踊っちゃだめ   etc…)

The last question (#3) is actually tricky since it can be interpreted in two ways:

  • Those shoes are not permitted or improper for dancing (maybe they scratch up the floor?)
  • It is impossible to dance in those shoes  (maybe they will be painful, or the high heel will break off immediately)





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3 thoughts on “Two types of “can’t” in Japanese: improper vs impossible

    1. locksleyu Post author

      I guess it is more traditional to write “wa” in this case, but I was just typing the romaji the same way I would write it in Japanese, using “ha” which represents the は character.

      Japanese is generally pretty consistent but this is one of the few exceptions in how characters are read..


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