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Grammar Book

GrammarBook N5: Adverbial Adjectives in Japanese (ku/ni)

  • 06 Feb, 2026
  • Com 0

N5-G-071

Adverbial Adjectives (く / に)

Supporting / Description

👀 Layer A: Visual Guide (直感理解)

📝 Quick Summary (まとめ)

形容詞を変化させて、動詞を詳しく説明する形(副詞)にします。「早い(Adjective)」を「早く(Adverb)」に変えて、「早く走る(Run fast)」のように使います。
Change Adjectives into Adverbs to describe actions. Use this to say *how* you do something (e.g., “clean neatly”, “wake up early”).

i-adj: い → く (Haya-ku)
na-adj: + に (Kirei-ni)

🔗 Connected Grammar (関連文法):

  • N5-G-046: ~なります (Become – Uses ku/ni)
  • N5-G-020: い-adjectives (Base)
  • N5-G-021: な-adjectives (Base)

🔍 Layer B: Deepening (深掘り)

💡 Raya’s Hack (攻略法)

「いい (Good)」は「よく (Well)」!
英語で “Good” (形容詞) と “Well” (副詞) が違うように、日本語でも形が大きく変わります。
* いい です (It is good.)
* **よく** できました (You did well.)
* **よく** 寝ました (I slept well.)
「いく」とは言いません。「よく」を使いましょう!

“Ii” (Good) transforms into “Yoku” (Well). Never say “Iku”. “Yoku” is used for “doing something well” or “often”.

🚧 Joy’s Mistake (よくある間違い)

Scene: Joy wants to say “Please speak slowly.”

Joy: 「ゆっくりな 話してください。」
(Yukkuri na hanashite kudasai.)

❌ Wrong Particle!

Why?

「ゆっくり (Slowly)」は副詞的に使う言葉なので、「な」は不要です。そのまま使うか、強調して「と」をつけることもありますが、「な」は間違いです。
正解は「**ゆっくり** 話してください」です。
※「静か(な)」はナ形容詞なので「静か**に** 話してください」となります。

“Yukkuri” is already an adverb. You don’t need “na” or “ni”. Just say “Yukkuri hanashite”. But for Na-adjectives like “Shizuka”, you MUST add “ni” -> “Shizuka NI hanashite”.

🔥 Layer C: Practice Loop

Now it’s time to test your learning through the next 10 practice drills!

Level 1: Change to Adverb (ku/ni)

Q1. Hayai (Fast/Early) -> Fast/Early

答え: 早く (Hayaku)

(i-adj: Drop i + ku)

Q2. Kirei (Clean/Pretty) -> Cleanly/Prettily

答え: きれいに (Kirei ni)

(na-adj: Add ni)

Q3. Oishii (Delicious) -> Deliciously

答え: 美味しく (Oishiku)

(i-adj: Drop i + ku)

Q4. Shizuka (Quiet) -> Quietly

答え: 静かに (Shizuka ni)

(na-adj: Add ni)

Q5. Ii (Good) -> Well

答え: よく (Yoku)

(Irregular)

Level 2: Describing Actions

Q6. I wake up early. (Hayai, Okiru)

答え: 早く 起きます。 (Hayaku okimasu.)

(How do you wake up? Early.)

Q7. Please write neatly. (Kirei, Kaku)

答え: きれいに 書いてください。 (Kirei ni kaite kudasai.)

(How do you write? Neatly.)

Q8. I bought it cheaply. (Yasui, Kau)

答え: 安く 買いました。 (Yasuku kaimashita.)

(How did you buy? Cheaply.)

Q9. He became strong. (Tsuyoi, Naru)

答え: 強く なりました。 (Tsuyoku narimashita.)

(Standard “Naru” pattern)

Q10. Translate: “I studied well.” (Ii, Benkyou suru)

答え: よく 勉強しました。 (Yoku benkyou shimashita.)

(Often / A lot / Well)


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Related posts:

GrammarBook N5 : AはBです (A is B) GrammarBook N5: The Particle も (also) GrammarBook N5: い-adjectives GrammarBook N5: ~たいです
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