Grammar Info

N5 Lesson 9: 8/13

なくてはいけない

Must do, Have to do

Also used to express duty or necessity. Click here if you are curious about なくて conjugation

Structure

Verb[ない+ なくては + いけない
Verb[ない+ なくちゃ + いけない

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

About なくてはいけない

Much like てはいけない, なくてはいけない states that something 'must not' be done. However, this is where the similarities end. なくてはいけない 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. いけない simply means 'cannot go', and comes from the negative potential form of ()く.
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 いけない.
  • 今日(きょう)()()なくてはいけない
    Today, I must sleep at 9. (I must not, not do it)
  • 明日(あした)彼女(かのじょ)誕生日(たんじょうび)プレゼント()なくてはいけない
    I must buy my girlfriend's birthday present tomorrow. (I must not, not do it)
  • 明日(あした)友達(ともだち)()から(いえ)掃除(そうじ)なくてはいけない
    Since my friend is coming tomorrow, I must clean my house. (I must not, not do it)
いけない is considered to be the most common structure used with the 'must', and 'must not' grammar points, and is natural in both speech, and written Japanese. Alternatively, ならない may be used in formal speech, but is much better suited to writing. だめ is also acceptable, but much more casual than either いけない or ならない.
  • 朝食後(ちょうしょくご)(くすり)()なくてはならない
    After breakfast, I must drink my medicine.
  • 野菜(やさい)()なくてはダメ
    You must also eat vegetables.
Caution
The ては in なくては is often converted to ちゃ, as this is easier to say. なくちゃ may then be followed by いけない, or いけない may be omitted, without changing the meaning.
  • 土曜日(どようび)会社(かいしゃ)()なくちゃいけない
    I gotta go to the company on Saturdays too.
  • 今日(きょう)スーパー()なくちゃ
    Today, I gotta go to the supermarket.
These casual structures are very similar to words like 'gotta' in English.

Examples

  • テスト(まえ)、よく()なくてはいけない

    Before a test, you must sleep well.

  • 12(がつ)なってから暖房(だんぼう)つけなくてはいけない

    Once December comes, you have to turn on the heating.

  • 来週(らいしゅう)試合(しあい)があるのでたくさん練習(れんしゅう)なくてはいけない

    Because I have a game next week, I must train a lot.

  • 今日(きょう)いい天気(てんき)だから(そと)(あそ)なくてはいけない

    Because the weather is nice today, I have to play outside.

  • まだやりたいことがあるけどもう()なくてはいけない

    There are still things that I want to do, but I have to sleep already.

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なくてはいけない – Grammar Discussion

Most Recent Replies (21 in total)

  • nekoyama

    nekoyama

    About 1 year ago

    This “long form” and “short form” isn’t a grammar term; it refers to whether bunpro wants an unabbreviated way to say “must” or a shorter, more colloquial one (e.g. なくてはいけない vs なくちゃ).

    て and ば refer to which pattern to say “must” is used (…なくては… vs. …なければ…, and …ないと… also exists).

    いく refers to which word is used in the second part (いけない / ならない / だめ) if one exists.

  • Marcus

    Marcus

    About 1 year ago

    Thank you so much! I’m going to be copying all that down in a minute, it’s so useful. I really, really struggle with Japanese and this grammar is killing me, but your answer helps a lot! Thank you so much! Much appreciated!

  • Asher

    Asher

    About 1 year ago

    Thanks for the reply here @nekoyama ! Yes, the long form/short form hints are actually just abbreviated/unabbreviated. The ‘tense’ hints are something that we will be making universal between all grammar points in the very near future, with as clear language as possible. There are still a lot of questions in the database that use things that are a little sub-optimal right now.

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