くない

い-adjective Negation

Level 1Sounds Like i

To say something is 'not [adjective]' in Japanese, you change the ending of the い-adjective from 〜い to 〜くない.

How It Works

In Japanese, negating an adjective isn't just adding a word like 'not'; it involves changing the word itself.

1. The Basic Rule:
Take the dictionary form of an い-adjective, remove the final い, and add くない.

  • 安い（やすい - cheap）→ 安くない（やすくない - not cheap）
  • 寒い（さむい - cold）→ 寒くない（さむくない - not cold）

2. Politeness Levels (Present Tense):

  • Casual: Just use 〜くない (e.g., 寒くない).
  • Polite: Add です after the negative form (e.g., 寒くないです).
  • Formal: Use the form 〜くありません (e.g., 寒くありません). This is common in business or writing.

3. Past Negative Forms:
To express that something was "not [adjective]" in the past, use the following endings:

  • Casual: Replace the final い of the negative form with かった to get 〜くなかった (e.g., 寒くなかった - was not cold).
  • Polite: Add です to the casual past negative (e.g., 寒くなかったです) or use the formal 〜くありませんでした.

4. The Irregular Exception:
The adjective いい (good) is special. You must use its alternative stem よ before adding any negative or past endings. It becomes よくない. This also applies to compound adjectives where "good" is the final component, such as かっこいい (cool) becoming かっこよくない or 気持ちいい（きもちいい - feels good）becoming 気持ちよくない.

Note: This rule does not apply to other adjectives that simply end in the sound "ii," such as 美味しい（おいしい - delicious）or 美しい（うつくしい - beautiful）. These follow the standard rule (e.g., 美味しくない).

Examples (4)

  1. この本は面白くないです。

    This book is not interesting.

    Word by Word: This book (topic) interesting-not is.

    面白（おもしろ）い becomes 面白くない. Adding です makes it polite.

  2. 今日はあまり寒くない。

    It’s not very cold today.

    Word by Word: Today (topic) not-very cold-not.

    This is a casual sentence. The word あまり is often used with negative forms to mean 'not very'.

  3. そのテストはよくありませんでした。

    That test was not good.

    Word by Word: That test (topic) good-not-was (formal).

    This uses the formal negative form (〜くありません) in the past tense (〜でした). Note that いい changed to よく.

  4. このカメラは高くありません。

    This camera is not expensive.

    Word by Word: This camera (topic) expensive-not (formal).

    高い（たかい） becomes 高くありません in formal speech.

Common Mistakes

  • Using 〜じゃない with い-adjectives.

    高いじゃないです。
    高くないです。

    〜じゃない is only for nouns and な-adjectives. い-adjectives must use the 〜くない conjugation.

  • Forgetting to drop the final い.

    おもしろいくないです。
    おもしろくないです。

    You must remove the original い before adding くない. Don't leave it in!

  • Treating きれい as an い-adjective.

    きれくないです。
    きれいじゃないです。

    Even though きれい ends in 'i', it is a な-adjective. Therefore, it follows the な-adjective negation rules.

How It Connects

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くないLevel 1い-adjective Negation

Learn This First

Negating い-adjectives involves a specific morphological change (replacing the final 'い' with 'くない'). Therefore, a learner must be able to identify い-adjectives and understand their basic function in a sentence before learning this conjugation rule.

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Patterns that build on this one.

Words in This Pattern

無い