Grammar Info
N4 Lesson 9: 9/15

なければならない
must do, have to do

Verb[ない]+と+いけない/ならない is also used to express duty or necessity.

Structure
Casual
Formal
Verb[ない] + ければ + ならない
Verb[ない] + きゃ + ならない
Verb[ない] + ければ + なりません
Verb[ない] + きゃ + なりません
Details
Register Formal
使用域 硬い
Information
Like なければいけない, なければならない is a structure that implies that something ‘must be done’. However, it is important to remember that this is actually a double negative, and therefore means ‘If (A) is not done, it cannot become’, or more simply ‘(A) cannot not be done’.
To make this construction, the auxiliary verb ない will need to be conjugated with , creating なければ (if not). After this, ならない (to not become) will be added to the end.
  • 仕事(しごと)なければならない
    I must do my work.
  • 先輩(せんぱい)部屋(へや)に入(はい)って来(き)たら立(た)っ挨拶(あいさつ)なければならない
    If your senpai comes into the room, you must stand and greet them.
As we learned in the なきゃ lesson, なければ may be shortened to なきゃ. This structure is frequently used, either with or without the added ならない.
  • 今日(きょう)帰(かえ)り遅(おそ)くなったら妻(つま)に怒(おこ)られるから、もうすぐ帰(かえ)らなきゃ
    My wife is going to scold me if I come home late today too, so I have to go home soon.
  • 今日(きょう)家事(かじ)やらなきゃならないから出(で)かけられない
    I have to do some chores today, so I can't go out.
Caution
While いけない (to not be able to go) and ならない (to not become) are quite similar, ならない will rarely be used outside of formal situations, or in writing. Due to this, いけない will be heard much more frequently in speech (when it is not omitted).
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たくない時(とき)でも宿題(しゅくだい)なければならない
Even when you don't want to, you have to do your homework.
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飛行機(ひこうき)乗(の)りたいなら、空港(くうこう)行(い)かなければならない
If you want to ride an airplane, you have to go to the airport.
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先生(せんせい)話(はなし)聞(き)かなければならない
You have to listen to the teacher (talk).
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Books
みんなの日本語 I
Page 110 [CH 17]
Tobira
Page 43
[DBJG] A Dictionary of Basic Japanese Grammar
Page 274
Tae Kim's Japanese Grammar Guide
Page 142