Grammar Info
N5 Lesson 9: 9/13

なくてはならない
Must do, Have to do

Also used to express duty or necessity. If you are curious about なくて conjugation

Structure
Casual
Formal
Verb[ない+ なくては + ならない
Verb[ない+ なくちゃ + ならない
Verb[ない+ なくては + なりません
Verb[ない+ なくちゃ + なりません
Details
Part of Speech Expression
Word Type Auxiliary Verb
Register Formal
品詞 表現
単語の種類 助動詞
使用域 硬い
Information
Much like てはならない, なくてはならない states that something ‘must not’ be done. However, this is where the similarities end. なくてはならない is an example of a double negative in Japanese, and actually has the meaning ‘(A) must be done’, or ‘must do (A)’.
While this grammar point is usually translated as ‘must do’, the literal translation is ‘must not, not do (A)’. This double ‘not’ is where many learners have difficulties. ならない simply means ‘cannot become’, and comes from the negative form of なる.
To use this structure, simply create the negative form of a verb, and then convert ない to なく (the conjunctive form of an い-Adjective), followed by . After this, is added, and then finally ならない.
  • 私(わたし)次(つぎ)バス停(てい)降(お)りなくてはならないです
    I have to get off at the next bus stop. (I must not, not do it)
  • トムタカお金(かね)返(かえ)さなくてはならないです
    Tom must give back money to Taka. (He must not, not do it)
  • 今日(きょう)漢字(かんじ)勉強(べんきょう)なくてはならないです
    I have to study kanji today. (I must not, not do it)
ならない is considered to be the most formal structure out of ならない, いけない, and だめ. It is regularly used in formal writing, or semi-formal/formal speech. いけない (the most common variation) and だめ (the most casual variation) are also acceptable in many situations.
  • レポート書(か)かなくてはいけない
    I must write a paper.
  • 食(た)べ前(まえ)に手(て)洗(あら)わなくてはダメ
    You must wash your hands before you eat.
Caution
The ては in なくては is often shortened to ちゃ, as this is easier to say. なくちゃ may then be followed by ならない. However, due to ならない being quite formal, なくちゃ (a casual structure) will not be used with ならない on a regular basis. It is more common to see なくちゃ paired with いけない, or だめ.
  • 今日(きょう)沢山(たくさん)走(はし)ったからシャワー浴(あ)びなくちゃならない
    Because I ran a lot today, I must take a shower.
  • バーベキュー肉(にく)持(も)っ行(い)かなくちゃいけない
    I gotta bring meat to the barbeque.
  • 冬(ふゆ)なる前(まえ)にキャンプ行(い)かなくちゃだめ
    We gotta go camping before it becomes winter, right?
These casual structures are very similar to words like ‘gotta’ in English.
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毎日(まいにち)勉強(べんきょう)なくてはならない
You must study every day.
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時(じ)半(はん)までに銀行(ぎんこう)行(い)かなくてはならない
By 3:30, I have to go to the bank.
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もう二(に)時(じ)ですまだお弁当(べんとう)食(た)べてないです食(た)べなくてはならない
It's already two?! I haven't eaten my bento yet. I have to eat.
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Books
Tobira
Page 43
Tae Kim's Japanese Grammar Guide
Page 142