N5 Lesson 9: 8/13
なくてはいけない なくてはいけない 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. If you are curious about なくて conjugation
Verb[ない+ なくては + いけない
Verb[ない+ なくちゃ + いけない
Verb[ない+ なくては + いけません
Verb[ない+ なくちゃ + いけません
No detail information for 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 行(い)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)9時(じ)寝(ね)なくてはいけない
    Today, I must sleep at 9.
  • 明日(あした)彼女(かのじょ)誕生日(たんじょうび)プレゼント買(か)わなくてはいけない
    I must buy my girlfriend's birthday present tomorrow.
  • 明日(あした)友達(ともだち)来(く)るから、家(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.
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)薬(くすり)飲(の)まなくてはならない
    After breakfast, I must drink my medicine.
  • 野菜(やさい)食(た)べなくてはダメ
    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)行(い)かなくちゃいけない
    I must go to work on Saturdays too.
  • 今日(きょう)スーパー行(い)かなくちゃ
    Today, I must go to the supermarket.
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The JLPT is tomorrow, so I must buy a pencil.
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Tae Kim's Japanese Grammar Guide
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