How to conjugate いい [ii] (=good)

This post provides important additional information for the post “い-adjective & な-adjective : Introduction.”

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いい (=good)

いい [ii] means “good,” and it is classified as an い-adjective.However, いい does not fully follow the normal い-adjective conjugation rules.

For the present affirmative (“is good”), いい becomes いいです, which follows the regular い-adjective pattern.However, for the negative and past tenses, we conjugate よい instead of いい.

◼️ Conjugation of いい

いい (=good)
いい です (= is good) Just attach です [desu] to いい	よ かった です (= was good) Conjugate as よい. Remove い [i] at the end, then attach かったです [kattadesu]
よ く ない です (= is not good) Conjugate as よい. Remove い [i] at the end, then attach くないです [kunaidesu]	よ く な かった です (= was not good) Conjugate as よい. Remove い [i] at the end, then attach くなかったです [kunakattadesu]

Examples

• きょう、てんきは いいです。

  The weather is good today.

  
  

• あした、てんきは よくないです。

  The weather will not be good tomorrow.

  
  

• きのう、てんきは よかったです。

  The weather was good yesterday.

  
  

• おととい、てんきは よくなかったです。

  The weather was not good the day before yesterday.

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かっこいい vs. かわいい

かっこいい [kakkoii] (“good-looking,” “cool”) conjugates the same way as いい (“good”).

This is because かっこいい is made up of two words:

• かっこう [kakkou]（格好 かっこう）= shape, figure, appearance

• いい [ii] = good

  
  

Since the いい in かっこいい truly means “good,” it changes to よい in negative and past forms.

かっこいい (=good looking, cool)
かっこいい です (= is good looking) Just attach です [desu] to かっこいい	かっこよ かった です (= was good looking) Conjugate as かっこよい. Remove い [i] at the end, then attach かったです [kattadesu]
かっこよ く ない です (= is not good looking) Conjugate as かっこよい. Remove い [i] at the end, then attach くないです [kunaidesu]	かっこよ く な かった です (= was not good looking) Conjugate as かっこよい. Remove い [i] at the end, then attach くなかったです [kunakattadesu]

On the other hand, かわいい [kawaii] (“cute”) is a single word.The いい in かわいい is not the adjective “good,” but simply part of the word itself.

Therefore, かわいい conjugates like a normal い-adjective.

かわいい (=cute)
かわいい です (= is cute) Just attach です [desu] to かわいい	かっこよ かった です (= was good looking) Remove い [i] at the end, then attach かったです [kattadesu]
かわい く ない です (= is not good looking) Remove い [i] at the end, then attach くないです [kunaidesu]	かっこよ く な かった です (= was not good looking) Remove い [i] at the end, then attach くなかったです [kunakattadesu]