Making Adverbs from Adjectives形容詞から副詞へ
Japanese has a clean, predictable system for turning adjectives into adverbs. For い-adjectives, drop い and add く: 速い → 速く (quickly). For な-adjectives, add に to the stem: 静か → 静かに (quietly). These adverbs modify verbs, telling you HOW an action is performed.
Japanese has a clean, predictable system for turning adjectives into adverbs. For い-adjectives, drop い and add く: 速い → 速く (quickly). For な-adjectives, add に to the stem: 静か → 静かに (quietly). These adverbs modify verbs, telling you HOW an action is performed.
い-adjectives → adverbs: い → く
Drop the final い and add く. This is the same く that appears in the negative (くない) and て-form (くて). Examples: 速い → 速く (fast), 強い → 強く (strongly), 早い → 早く (early), 大きい → 大きく (greatly), 美しい → 美しく (beautifully). These adverbs typically appear right before the verb they modify: 速く走る (run fast), 早く起きる (wake up early).
な-adjectives → adverbs: stem + に
Add に to the adjective stem. Examples: 静か → 静かに (quietly), きれい → きれいに (neatly/beautifully), 上手 → 上手に (skillfully), 丁寧 → 丁寧に (carefully/politely). These also appear before verbs: 静かに話す (speak quietly), きれいに書く (write neatly).
Adverb + なる = "become ~"
One of the most important patterns using adverbial forms is ～くなる (for い-adj) and ～になる (for な-adj), meaning "become ~." 大きい → 大きくなる (become big), 暖かい → 暖かくなる (become warm), 元気 → 元気になる (become healthy), 上手 → 上手になる (become skilled). This pattern is used constantly in daily Japanese.
Adverb + する = "make ~"
Similarly, ～くする and ～にする mean "make something ~": 大きい → 大きくする (make bigger), 小さい → 小さくする (make smaller), きれい → きれいにする (make clean), 静か → 静かにする (make quiet). Example: テレビの音を小さくする (turn down the TV volume).
Adjective to adverb conversion
| Type | Adjective | Adverb | Example sentence |
|---|---|---|---|
| い-adj | 速い (fast) | 速く | 速く走る (run fast) |
| い-adj | 早い (early) | 早く | 早く起きる (wake up early) |
| い-adj | 強い (strong) | 強く | 強く押す (push hard) |
| な-adj | 静か (quiet) | 静かに | 静かに話す (speak quietly) |
| な-adj | きれい (neat) | きれいに | きれいに書く (write neatly) |
| な-adj | 上手 (skilled) | 上手に | 上手に弾く (play skillfully) |
| irregular | いい (good) | よく | よくできた (well done) |
Example sentences
速く走ってください。
Hayaku hashitte kudasai.
Please run fast.
い → く: 速い → 速く
静かに食べなさい。
Shizuka ni tabenasai.
Eat quietly.
な-adj + に: 静か → 静かに
日本語が上手になった。
Nihongo ga jouzu ni natta.
I’ve become good at Japanese.
になる = become ~
部屋を暖かくした。
Heya o atatakaku shita.
I made the room warm.
くする = make ~
よく分からない。
Yoku wakaranai.
I don’t really understand.
いい → よく (irregular adverb)
Common mistakes
速いに走る
速く走る
い-adjectives use く for the adverbial form, not に. に is only for な-adjectives.
静かく話す
静かに話す
な-adjectives use に for the adverbial form, not く. く is only for い-adjectives.
いいく分かる / いく分かる
よく分かる
いい is irregular. Its adverbial form is よく, following the よ- stem. There is no いく in Japanese.
Frequently asked questions
What is the difference between 速く and 速い?
速い is the adjective (modifies nouns: 速い車 = fast car). 速く is the adverb (modifies verbs: 速く走る = run fast). English uses "fast" for both, but Japanese requires the correct form.
Can I use よく to mean "often"?
Yes! よく has two meanings as an adverb: "well" (よくできた = well done) and "often/frequently" (よく行く = go often). Context makes the meaning clear.
Does every adjective have an adverb form?
Yes. Every い-adjective and な-adjective can be converted to an adverb using the く / に rule. Whether the resulting adverb sounds natural depends on context, but the grammar always works.
What is the adverb of 速い?