第103課: Must Not

In this lesson, we will learn about the phrases for “must not”. Now, contrary to what many textbooks may say, there are actually differences among the several options that you as the listener must understand. Before we study “must” phrases, it’s important to learn about the “must not” phrases because there are fewer of them and less information overall to go through. So, let’s begin. 



  • 動詞: 連用形 + ては+ならない・いけない・だめだ
  • 形容詞: 連用形(く) + ては+ならない・いけない・だめだ
  • 名詞・形容動詞: 連用形(で) + は+いけない・だめだ/ではあっては+ならない・いけない
Contraction NoteIn casual speech ては → ちゃ では →じゃ 
 使っては → 使っちゃ 死んでは → 死んじゃ


~てはならない: A prohibitory command accompanied with a sense of societal duty. This is the only pattern appropriate for law documents or judicial verdicts. It is obligatory in the written language in showing commands that regard society. 

~てはいけない: A prohibitory command accompanied with a sense of personal duty. ~てはならない would be more stern than ~てはいけない in this situation in the written language.  

~てはだめだ: A prohibitory command projecting warning, chastise, or criticism to the listener. It may not always be a literal command. It may simply suggest prohibition or avoidance of an action. It may also be used to encourage someone like in “don’t give up”: 諦めてはだめだ!This pattern is used primarily in the spoken language. 

Spelling Note: These phrases are typically spelled in ひらがな. However, だめ is frequently spelled in 漢字 as 駄目.

In the spoken language, there is a lot of interchangeability between ~てはいけない and ~てはだめだ, and in the written language, there is a lot of interchangeability between ~てはならない and ~てはいけない.

1. 日本は、憲法(けんぽう)()らして、いかなる武器(ぶき)も保持してはならない。(Formal document; 書き言葉)
   Japan must not maintain any arms in light of the constitution. 

2a. 町民(ちょうみん)(とう)は、いかなる理由(りゆう)にせよ、廃棄物(はいきぶつ)不法(ふほう)投棄(とうき)してはならない。 (法律; 書き言葉)
2b. 市民は、いかなる理由であっても、廃棄物を不法投棄してはならない。(書き言葉)
     Townspeople must by no reason unlawfully dump waste matter. 

3. この薬は副作用(ふくさよう)があり、血糖値(けっとうち)の上昇を引き起こす可能性(かのうせい)があるので、2日以上(いじょう)連続(れんぞく)して服用(ふくよう)しては{ならない・いけない}。(書き言葉)
There are side effects to this drug with one being a possible rise in blood sugar. So, you mustn't use it more than two days consecutively. 

 The Person Commanding

If we think of who makes the command, the person is of a higher status than the listener. It does not necessarily have to be the speaker who is the commander. The commander is likely as such based on what exactly you use.

 Pattern Style? Description of Use
 ~てはならない 書き言葉 Commanded person is an overseeing/administering agency.
 ~てはいけない Both Commanded person is a responsible party. 
 In the spoken language, it is mainly used by men.
 ~てはいけません 話し言葉 Used mainly by women: mothers, teachers, and bosses
 ~てはだめだ 話し言葉 Used mainly by men: fathers, teachers, bosses, and sempai. 
 ~てはだめです 話し言葉 Used mainly by women: mothers, teachers, bosses, and sempai.

Speech Style Note: If a man is to use the non-敬語 phrases ~てはいけない and ~てはだめだ and they are not a person of ultimate authority, one can imagine the speaker becoming in an emotional state in which he just ignores the character of the addressee.

~てはだめ(だよ・よ)when used among friend and family becomes advice rather than a straight out command and can be used to one’s technical superior and inferior in this situation.

4. お母さん、そんなに働いちゃだめよ。体を壊しちゃうわ。(女性語)
    Mom, don't work so hard like that. You'll get sick. 

5. そのぬいぐる、まだ持ってたの?ルパートは危ないから、持ってちゃだめだよ。捨てなさい。(Family Guy reference)
You still have that stuffed animal? I told you that Rupert was dangerous, so you can't keep him. Throw him away. 

 Gender Trend?

It is not that ~てはいけません and ~てはだめです are exclusively used by women, but women are often expected to be more polite. So, in this sense, regardless of whether one is male or female, the use of these polite forms emphasizes ones class more than actually showing respect to the addressee. This is expected of any well-educated 成人.

6a. 今日は、自分の車で帰るつもりでしょう?お酒を飲んでは{いけません・だめです}よ。(敬意けいい
b. 今日は、車で帰る?じゃ、飲んじゃ{いけません・だめです}よ。(品格ひんかく保持ほじ

6a. Aren't you going home in your own car today? You mustn't drink.
6b. You're going home by car today? Well, you mustn't drink.      

Grammar NoteNot using polite forms of conjunctive phrases makes it clear whether someone is showing 敬意 (respect) or 品格保持 (societal standing). This would show the latter.

 More on ~てはならない

Using ~てはならない in things based on personal experience and knowledge in spoken, colloquial contexts is unnatural except in dramas and movies. 

7. 敵に後ろを見せるのかい。そりゃならぬ。武士として、あるまじきことじゃ。  (Samurai talk)
   Show our rear to the enemy? That mustn't happen. That is unworthy of a warrior. 

The Difference between ~てはいけない & ~てはだめだ

When ~てはいけない is used, there is a rule that needs to be protected/followed, and if one breaks the rule, punishment follows. When ~てはだめだ is used, it is most often the case that there is no penalty or responsibility implied for the addressee. Even if there isn’t a rule to follow, if you are scolded or are to run into an unpleasant circumstance, it becomes understood to the speaker and listener that there is an unwritten rule to abide by.

8. ご飯を食べたら、すぐにお風呂! それまでゲームをやっては{いけません・だめです}よ。
   Bath right after supper! Until then, you must not play video games. 

9. こんなに雨が降ってきては{だめだ 〇・いけない X}、計画は中止だ。
   This can't do with all rain falling like this; plans are cancelled. 

It’s impossible for man to actually command the weather. So, in this sentence, using ~てはいけない is just wrong. 

Summary Chart

  書き言葉 話し言葉 ばつ・ペナルティ 命令めいれいぶん 非命令ひめいれいぶん
 ~てはならない 〇 X  〇 〇 X
 ~てはいけない 〇 〇 〇 〇 △
 ~てはだめだ X 〇 X 〇 〇

Definition Notes: 罰 = Punishment; 命令文 = Imperative sentence; 非命令文 = Non-imperative sentence


First, before we look at how these phrases differ with the ones above, consider the conjugation rules below.  

  • 動詞:終止形+と{いけない・だめだ}
  • 形容詞・形容動詞:終止形+{といけない・だめだ}
  • 名詞:である・だ+(といけない・だめだ)

As you can see, there is no ~とならない. You can’t use ~といけないand ~とだめだ to make sentences that urge someone. They may be used in declarative and affirmation sentences, but they can’t be interpreted as prohibitory commands.

と marks a general condition, and it can only be used with confidence based on personal experience and or knowledge. So, even if you were to tell a listener a message involving having been prohibited, the use of these options would still be unnatural. As ~てはならない exists as an absolute prohibitory imperative phrase, there’s no way a declarative ~とならない could exist.

10. 心臓しんぞう悪いから、歩くのはいいが、走ると{いけない・だめな}のだ。   (書き言葉)
      My heart is not good, so it's OK for me to walk, but I can't run. 

More Examples

11. 子供はお酒を飲んではいけない。 
      Children must not drink sake.

12. の中では走ってはいけませんよ。
      You must not run in the middle of the house!

13. おくれちゃだめ(だよ)。
   You can't be late!