いい

いい is an い-adjective meaning **"good"**. It is one of the most common adjectives in Japanese, but it has an **irregular conjugation** that learners must memorize. While the dictionary form is いい, all conjugated forms are based on its older form よい.

Conjugation

Unlike regular い-adjectives where you simply drop い and add the ending, いい reverts to よい before conjugating:

• Non-past: いい / よい

  このほん本はいい。

  This book is good.

• Negative: よくない

  てんき天気がよくない。

  The weather is not good.

• Past: よかった

  えいが映画はよかった。

  The movie was good.

• Past negative: よくなかった

  きのう昨日のしあい試合はよくなかった。

  Yesterday's game was not good.

• て-form: よくて

  せいせき成績がよくて、うれしい嬉しい。

  My grades are good, so I'm happy.

• Adverbial form: よく

  よくきいてください聞いてください。

  Please listen well.

• Conditional: よければ

  よければ、いっしょに一緒にいきません行きませんか。

  If it's okay with you, would you like to go together?

A common mistake is to conjugate directly from いい (e.g., ×いくない, ×いかった). Always use the よ- stem for conjugated forms.

Common expressions

いい appears in many everyday phrases:

• いいてんきいい天気 – nice weather

  きょう今日はいいてんきいい天気ですね。

  It's nice weather today, isn't it?

• もういい – "enough already" or "it's fine now"

  もういいよ。

  That's enough. / It's fine now.

• いいですね – "that's nice" or "sounds good"
• いいですよ – "sure, that's fine" (giving permission)

いい vs. よい

よい can also be used as the dictionary form, especially in formal writing or set phrases. In everyday conversation, いい is far more common.