Grammar Info
N5 Lesson 9: 12/13

なくちゃ・なきゃ
Must do, Have to do

Common abbreviations

Structure
Casual
Formal
Verb[ない] + きゃ(1) + いけない
Verb[ない] + くちゃ+ いけない

(1) なけりゃ
Verb[ない] + きゃ(1) + いけません
Verb[ない] + くちゃ+ いけません

(1) なけりゃ
Details
Part of Speech Expression
Register Casual
品詞 表現
単語の種類 砕けた言い方
使用域 タメ語
Information
なくちゃ (short forなくては), and なきゃ (short for なければ) are the most common colloquial abbreviations used to convey that something ‘must’, or ‘has to’ be done.
Like てはいけない (must not), なくてはいけない (must), and なくてはならない (must), these abbreviation forms can be followed by いけない, ならない, or だめ. However, they are usually omitted, without changing the meaning.
Structures like this are called 口語(こうご) (spoken/colloquial language) in Japanese. These casual variations can come across in a very similar way to words like ‘gotta’ in English.
  • 今日(きょう)家(いえ)掃除(そうじ)なきゃだめだから、遊(あそ)ばない
    Since I must tidy up the house today, I won’t hang out.
  • 野菜(やさい)食(た)べなくちゃいけない。
    I must eat vegetables.
  • あっ、洗濯(せんたく)なきゃ
    Oops, I gotta do laundry.
  • 宿題(しゅくだい)なくちゃ
    I gotta do my homework.
In these examples, a variety of forms have been used naturally. There is no ‘most natural’ form, and it will often depend on the speaker as to which they choose.
As with almost all grammatical structures, the shortest variations (not including いけない, etc.) are the most casual/used the most often.
There are several other ways that these common abbreviations can appear based on region, or even an individual speaker's preference. An example of this is なけりゃ, which is a (very) casual form of なければ.
  • お前(まえ)やらなけりゃだめだろ
    You must do it! (Why aren't you doing what you must do?)
In this example, we can see that some of these less common variations are used specifically by certain genders (in general). なけりゃ itself tends to be used by male speakers, and may be considered a bit rougher than なきゃ, or なくちゃ, which can be used by anybody.
Slow Male
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日本語(にほんご)勉強(べんきょう)なくちゃいけない
You must study Japanese.
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暑(あつ)いので水(みず)飲(の)まなきゃいけない
Since it is hot, you must drink water.
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もっと文法(ぶんぽう)勉強(べんきょう)なくちゃいけない
I must study more grammar.
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Books
Genki I
Page 233
Genki I 2nd Edition
Page 273
Tae Kim's Japanese Grammar Guide
Page 144