Adjectives as Adverbs in Japanese

Overview

In English, you often add "-ly" to an adjective to make it an adverb: "quick" becomes "quickly." Japanese has a similarly straightforward system for converting adjectives into adverbs, but the transformation depends on which type of adjective you are working with. Since Japanese has two main adjective classes -- い-adjectives and な-adjectives -- there are two conversion patterns to learn.

This is a CEFR A1 concept, and it is one of the first ways you will start building more expressive sentences. Instead of just saying "the music is quiet," you can say "please speak quietly." Adverbs let you describe how actions are performed, making your Japanese sound more natural and precise from the very beginning.

Mastering these two simple rules unlocks a huge amount of vocabulary, because every adjective you already know can now also function as an adverb. This is an efficient way to expand your expressive range without learning new words.

How It Works

い-Adjectives: Drop い, Add く

Remove the final い and replace it with く.

Adjective	Meaning	Adverb	Meaning
速い (hayai)	fast	速く (hayaku)	fast/quickly
早い (hayai)	early	早く (hayaku)	early
高い (takai)	high/expensive	高く (takaku)	highly/expensively
安い (yasui)	cheap	安く (yasuku)	cheaply
強い (tsuyoi)	strong	強く (tsuyoku)	strongly
大きい (ookii)	big	大きく (ookiku)	greatly/in a big way
良い (yoi/ii)	good	良く/よく (yoku)	well/often

Note that いい (good) is irregular -- its adverb form is よく (yoku), based on the older form 良い (yoi).

な-Adjectives: Add に

Simply attach に to the adjective stem (the part before な).

Adjective	Meaning	Adverb	Meaning
静か (shizuka)	quiet	静かに (shizuka ni)	quietly
上手 (jouzu)	skillful	上手に (jouzu ni)	skillfully
きれい (kirei)	clean/pretty	きれいに (kirei ni)	cleanly/beautifully
簡単 (kantan)	simple	簡単に (kantan ni)	simply/easily
丁寧 (teinei)	polite/careful	丁寧に (teinei ni)	politely/carefully

Word Order

Adverbs typically come directly before the verb they modify:

[Subject は] + Adverb + Verb

• 彼は速く走ります。(kare wa hayaku hashirimasu) -- He runs fast.
• 静かに食べてください。(shizuka ni tabete kudasai) -- Please eat quietly.

Examples in Context

Japanese	English	Note
速く走ります。(hayaku hashirimasu)	I run fast.	い → く
静かに話してください。(shizuka ni hanashite kudasai)	Please speak quietly.	な-adj + に
上手に歌います。(jouzu ni utaimasu)	I sing well.	な-adj + に
早く起きました。(hayaku okimashita)	I woke up early.	い → く
大きく書いてください。(ookiku kaite kudasai)	Please write it big.	い → く
きれいに掃除しました。(kirei ni souji shimashita)	I cleaned it neatly.	な-adj + に
安く買いました。(yasuku kaimashita)	I bought it cheaply.	い → く
簡単に説明します。(kantan ni setsumei shimasu)	I will explain simply.	な-adj + に
よく分かりました。(yoku wakarimashita)	I understood well.	Irregular: いい → よく
丁寧に書きます。(teinei ni kakimasu)	I write carefully.	な-adj + に
強く押してください。(tsuyoku oshite kudasai)	Please push hard.	い → く
彼女は上手にピアノを弾きます。(kanojo wa jouzu ni piano o hikimasu)	She plays the piano well.	Full sentence with topic

Common Mistakes

Using な instead of に for adverbs

• Wrong: 静かな話してください。
• Right: 静かに話してください。
• Why: な connects an adjective to a noun (静かな部屋 -- a quiet room). To modify a verb, you need に.

Forgetting to drop い before adding く

• Wrong: 速いく走ります。
• Right: 速く走ります。
• Why: You must remove い before adding く. The い is replaced, not kept.

Using いい instead of よく

• Wrong: いいく分かりました。
• Right: よく分かりました。
• Why: いい is an irregular adjective. Its conjugated forms all come from 良い (yoi), so the adverb is よく (yoku).

Confusing adverb position

• Wrong: 走ります速く。
• Right: 速く走ります。
• Why: Adverbs come before the verb they modify. Placing them after the verb sounds unnatural.

Practice Tips

• Convert your existing adjective vocabulary. Go through all the い-adjectives and な-adjectives you know and write out their adverb forms. This reinforces the pattern while expanding your active vocabulary.

• Describe daily actions with adverbs. As you go through your day, narrate what you do: 早く起きます (I wake up early), 静かに食べます (I eat quietly), よく勉強します (I study well). This builds the habit of using adverbs naturally.

• Listen for adverbs in native content. When watching Japanese media, pay attention to words ending in く or に before verbs -- you will start recognizing the pattern everywhere.

Related Concepts

• Prerequisite: い-Adjectives -- you need to know い-adjectives before converting them to adverbs
• Next steps: Becoming なる/する -- use adverb forms with なる to express change of state (高くなる -- become expensive)