(Joy saying “Ii!” casually vs. Joy writing “Yoi” formally)
“Today is a good day.” (Kyou wa ii tenki desu.)
“Yesterday was a good day.” (Kinou wa ikatta… wait, yokatta?)
Both よい (Yoi) and いい (Ii) mean “Good.” But they have strict rules about when you can use them. If you make a mistake, it sounds very strange! Let’s master the rules with Joy and Ken.
🗣 Conversation Scene
Joy is talking about a movie she saw yesterday.
(Ken-san, yesterday’s movie was very “ikatta” [good]!)
「いい」は過去形（かこけい）にできませんよ！
(Hmm? Joy, not “ikatta,” but “yokatta.” You cannot conjugate “ii” into past tense!)
💡 Explanation
Basically, Ii is for speaking now. Yoi is for changing forms (grammar).
Rule 1: “Ii” cannot change!
You can use いい (Ii) only in the Present Tense dictionary form. It sounds casual and conversational.
- それは いい ですね。 (That is good.)
- いい 天気（てんき）ですね。 (Nice weather.)
- 頭（あたま）が いい です。 (He is smart.)
Rule 2: For conjugation, switch to “Yoi”
If you need Past Tense, Negative, or Te-form, you MUST use the base よい (Yoi).
Think of it as: “Ii” transforms into “Yo-“!
- Past: よかった (Yokatta) ❌ いかった
- Negative: よくない (Yokunai) ❌ いくない
- Te-form: よくて (Yokute) ❌ いくて
📊 Conjugation Table
🌟 Phrase Cheat Sheet
Some phrases are fixed!
✅ Must use “Ii”:
- いいね！ (Ii ne!) – Nice! / Like button
- いい加減 (Ii kagen) – Irresponsible / Good amount
- 仲がいい (Naka ga ii) – Good relationship
✅ Must use “Yoi” (Formal/Written):
- 良いお年を (Yoi otoshi o) – Have a good New Year
- 良い旅を (Yoi tabi o) – Have a good trip
- 用意 (Youi) – Preparation (Different word, but sounds similar!)
🚧 Joy’s Mistake
(Remembering yesterday’s lunch)
❌ Wrong: 昨日のランチは いかった です。
(Never conjugate “Ii”.)
✅ Right: 昨日のランチは よかった です。
(Use the “Yoi” base for past tense!)
🔥 Practice Quiz
Tap to check the answer!
