Grammar Info
N5 Lesson 1: 9/12

良(い)い
い-Adjective meaning 'good'

よく can also mean 'frequently/often', and has several different potential kanji

Structure
Casual
Formal
Non-Past Form: いい
Non-Past Negative Form: よくない
Past Form: よかった
Past Negative Form: よくなかった
Polite Non-Past Form: いいです
Polite Non-Past Negative Form: よくないです
Polite Past Form: よかったです
Polite Past Negative Form: よくなかったです
Details
Part of Speech Adjective
Word Type Independent Word
Register Standard
品詞 形容詞
単語の種類 自立語
使用域 一般
Information
いい is an adjective that means ‘good’ in Japanese. It can be a little bit difficult to use at first, as it conjugates differently to other い-Adjectives.
  • これいい映画(えいが)
    This is a good movie.
  • これ良(よ)くない。
    This is not good.
  • 昨日(きのう)天気(てんき)かった。
    Yesterday’s weather was good.
  • 昨日(きのう)天気(てんき)くなかった。
    Yesterday’s weather was not good.
In these sentences, we can see that the first い in いい changes to よ, depending on the form. This is unique to いい, and does not happen with other adjectives.
いい can sometimes be seen as 良(よ)い, in these cases, the kanji is likely to be read as よい, and not いい. There is technically no difference between these two meanings, but よい does sound more formal/old-fashioned.
  • これいい車(くるま)
    This is a good car.
  • これ良(よ)い
    This is also splendid. (‘Splendid’ is similar to the nuance that よい gives いい)
Caution
When used as an adverb, よく should not be confused as a conjugation of いい. よく has several possible kanji that it may stem from, and means frequently/often/well.
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いいです
(It is) good.
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これいいです
This is good.
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これいい本(ほん)です
This is a good book.
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Books
みんなの日本語 I
Page 56 [CH 8]
Tae Kim's Japanese Grammar Guide
Page 42