Adjectives as Adverbs in Japanese

In Brief

To make an い-adjective describe an action, replace its final い with く: 速い → 速く走る (“fast” → “run fast”). With a な-adjective, add に: 静か → 静かに話す (“quiet” → “speak quietly”). The important exception is いい (“good”), which becomes よく (“well” or “often”).

Overview

An adjective normally describes a noun: 速い電車 is “a fast train,” and 静かな部屋 is “a quiet room.” An adverb (a word or phrase that tells you how, when, or to what degree something happens) describes a verb or, in some cases, another adjective. To say that someone runs fast or speaks quietly, Japanese changes the adjective into an adverbial form.

This is an A1 pattern and one of the most useful reasons to learn the difference between the two main Japanese adjective classes. い-adjectives usually end in い in their dictionary form. な-adjectives use な before a noun, although their dictionary entry is normally shown without な. Each class has its own adverbial ending.

English often adds “-ly,” as in “quiet” → “quietly,” but the match is not exact. Japanese forms can express manner (“quietly”), degree (“greatly”), emotional attitude (“happily”), or a resulting state (“make it clean”). It is therefore better to learn the Japanese pattern than to search for an English “-ly” word every time.

How It Works

The two beginner rules

Adjective type	Before a noun	Adverbial form	With a verb
い-adjective	速い車, a fast car	remove final い + く: 速く	速く走る, run fast
な-adjective	静かな部屋, a quiet room	base form + に: 静かに	静かに話す, speak quietly

The adjective itself changes; the verb then behaves normally. For example, 速く走ります is polite, 速く走る is plain, and 速く走りました is past polite. The form 速く does not change for tense or politeness.

Forming adverbs from い-adjectives

Take the plain, non-past form ending in い, remove that final い, and add く.

い-adjective	Meaning	Adverbial form	Typical combination
速い（はやい）	fast, high-speed	速く	速く走る, run fast
早い（はやい）	early	早く	早く起きる, get up early
遅い（おそい）	late; slow	遅く	遅く帰る, return late
楽しい（たのしい）	enjoyable, fun	楽しく	楽しく話す, talk enjoyably
大きい（おおきい）	big, loud	大きく	大きく書く, write large
小さい（ちいさい）	small, quiet	小さく	小さく切る, cut small
強い（つよい）	strong	強く	強く押す, push hard
優しい（やさしい）	gentle, kind	優しく	優しく説明する, explain gently

Do not simply attach く to the full adjective. The final い is replaced: 速い + く is not 速いく but 速く.

Kanji helps distinguish two common words pronounced はやい. 速い concerns speed, so 速く走る means “run fast.” 早い concerns an early time, so 早く起きる means “get up early.” In speech, context supplies the distinction.

The exception: いい becomes よく

The common adjective いい (“good”) is irregular because many of its changed forms use the older base よ-. Its adverbial form is therefore よく, not ×いく.

• いい歌 — a good song
• よく歌う — sing well; sing often

Compounds ending in いい follow the same pattern: かっこいい (“cool; good-looking”) becomes かっこよく, as in かっこよく踊る (“dance stylishly”).

Be aware that よく has two frequent meanings. It can mean well, describing manner or quality, or often, describing frequency:

• 日本語をよく話します。— “They speak Japanese well.”
• よく図書館に行きます。— “I often go to the library.”

The surrounding sentence normally makes the intended meaning clear.

Forming adverbs from な-adjectives

Use the adjective’s base form and add に. Do not add な: な is used when the adjective directly modifies a noun.

な-adjective	Before a noun	Adverbial form	Typical combination
静か（しずか）	静かな場所, a quiet place	静かに	静かに話す, speak quietly
上手（じょうず）	上手な人, a skilled person	上手に	上手に歌う, sing well
丁寧（ていねい）	丁寧な説明, a careful explanation	丁寧に	丁寧に説明する, explain carefully
簡単（かんたん）	簡単な方法, an easy method	簡単に	簡単にできる, be able to do easily
元気（げんき）	元気な子, an energetic child	元気に	元気に遊ぶ, play energetically
きれい	きれいな部屋, a clean room	きれいに	きれいに掃除する, clean thoroughly/neatly
自由（じゆう）	自由な時間, free time	自由に	自由に選ぶ, choose freely

Although きれい ends in the hiragana い, it is a な-adjective. Its adverbial form is きれいに, not ×きれく. The same warning applies to 嫌い（きらい, “disliked; not fond of”), another common な-adjective that happens to end in い.

Basic sentence pattern

The usual order is:

[topic or subject] + [adverbial adjective] + [verb]

• 私は早く起きます。— I get up early.
• 田中さんは静かに話します。— Tanaka speaks quietly.

Japanese often leaves out the topic when it is already understood, so 早く起きました can simply mean “I woke up early” or “they woke up early,” depending on context.

Examples in Context

Japanese	English	Note
速く走ります。	I run fast.	速い → 速く; physical speed
静かに話してください。	Please speak quietly.	静か → 静かに before 話す
上手に歌います。	She sings well.	上手 is a な-adjective
今日は早く起きました。	I got up early today.	早い refers to time
名前を大きく書いてください。	Please write your name in large letters.	大きく describes how to write it
野菜を小さく切ります。	I cut the vegetables into small pieces.	The pieces become small
先生は文法を分かりやすく説明しました。	The teacher explained the grammar clearly.	分かりやすい → 分かりやすく
ドアをゆっくり閉めてください。	Please close the door slowly.	ゆっくり is already an adverb; it does not use these rules
子どもたちは元気に遊んでいます。	The children are playing energetically.	元気 → 元気に
このアプリは簡単に使えます。	This app can be used easily.	簡単に describes ease
部屋をきれいに掃除しました。	I cleaned the room thoroughly.	きれい is a な-adjective
もっと丁寧に書いてください。	Please write more carefully.	もっと increases the degree
みんなで楽しく食事をしました。	We all had an enjoyable meal together.	楽しい → 楽しく
このボタンを強く押さないでください。	Please do not press this button hard.	強く modifies a negative request
週末はよく映画を見ます。	I often watch movies on weekends.	よく expresses frequency here

These translations show the natural English meaning, not a word-for-word formula. For example, 楽しく食事をする is more naturally “have an enjoyable meal” than “eat enjoyably.”

Common Mistakes

Keeping the final い before く

• Wrong: ×速いく走ります。
• Right: 速く走ります。
• Why: For an い-adjective, replace the final い with く; do not add く after it.

Using く with a な-adjective

• Wrong: ×静かく話してください。
• Right: 静かに話してください。
• Why: 静か is a な-adjective, so its adverbial form takes に.

Putting な before the verb

• Wrong: ×静かな話します。
• Right: 静かに話します。
• Why: 静かな must be followed by a noun, as in 静かな人 (“a quiet person”). Before a verb, use 静かに.

Treating every word ending in い as an い-adjective

• Wrong: ×部屋をきれく掃除しました。
• Right: 部屋をきれいに掃除しました。
• Why: きれい is a な-adjective despite its final い. Learn its noun-modifying form, きれいな, as a clue to its class.

Making いい regular

• Wrong: ×いいくできました。
• Right: よくできました。
• Why: いい uses the irregular base よ- in this form. よくできました means “Well done” or “It was done well.”

Confusing 速く and 早く

• Wrong for “Please come early”: ×速く来てください。
• Right: 早く来てください。
• Why: 早く concerns an early time. 速く concerns speed. In some contexts both are possible but mean different things: 早く来る is “come early,” while 速く来る emphasizes coming quickly.

Usage Notes

The English translation may not end in “-ly”

Japanese adverbial adjectives often correspond to an English adverb, but natural English may use another structure. 小さく切る is literally close to “cut small,” but “cut into small pieces” is more idiomatic. 元気に遊ぶ can be “play energetically,” “play cheerfully,” or simply “be lively at play,” depending on context.

This also works in the other direction: not every English adverb comes from a Japanese adjective. ゆっくり (“slowly”), すぐ (“right away”), たくさん (“a lot”), and とても (“very”) are already used adverbially. Do not try to give them く or に endings.

Position is flexible, but keep the modifier clear

The adverbial form normally appears before the verb it describes, though other sentence elements may come between them. In 私は毎朝駅まで速く歩きます (“I walk quickly to the station every morning”), 速く remains connected in meaning to 歩きます. Beginners will usually sound clearest by placing it fairly close to the verb.

に has more than one job

The に in 静かに is the marker that creates the adverbial use of a な-adjective. Elsewhere, に can mark time, destination, a recipient, or other relationships. Its meaning comes from the construction: 静かに話す (“speak quietly”) is different from 学校に行く (“go to school”).

Politeness belongs mainly to the verb

The adjective-derived adverb does not become more polite by changing its ending. Compare 静かに話す, 静かに話します, and 静かに話してください. The level of formality and the type of sentence are shown by the verb ending.

Beyond the Basics: Results, Change, and Longer Forms

You do not need to master all of this at A1, but the same forms appear in several important later patterns.

Describing a resulting state

An adverbial adjective can describe not only how someone acts but also the state produced by the action:

• 部屋をきれいにする。— make the room clean
• 音を大きくする。— turn up the sound; make the sound louder
• 髪を短く切る。— cut one’s hair short

In 髪を短く切る, 短く can be understood as the result of cutting: the hair ends up short. Context tells you whether the form mainly expresses manner, result, or both.

Changes with なる and deliberate changes with する

The same く and に forms combine with なる (“become”) and する (“make; cause to be”):

Adjective type	Become	Make something…
い-adjective	暖かくなる, become warm	暖かくする, make it warm
な-adjective	静かになる, become quiet	静かにする, make it quiet / be quiet

This is why the pattern is sometimes called the adjective’s adverbial or continuative form rather than merely an “-ly form.” It participates in Japanese grammar more broadly than English “-ly” does.

Negative and linking forms

The negative form of an い-adjective also contains く: 高くない means “not expensive/high.” From there, forms such as 高くなくて can link ideas: この店は高くなくて、おいしいです (“This restaurant is not expensive and the food is good”). This く is historically and grammatically related, but forming adjective negatives and linking clauses is a separate topic. Do not confuse 高くない (“is not expensive”) with 高く買う (“buy at a high price”).

Forms that have become established expressions

Some adjective-derived forms are used so frequently that they feel like independent adverbs. よく can mean “often,” and 多く（おおく） often means “many” or “widely” in more formal phrases such as 多くの人 (“many people”). Such meanings are best learned in complete expressions rather than predicted only from the basic conversion rule.

Practice Tips

1. Learn adjectives in contrasting pairs. Say the noun form and verb form together: 速い車／速く走る, 静かな部屋／静かに話す. This reinforces both the adjective class and the correct ending.
2. Describe everyday actions. Make short sentences about your routine: 早く起きる, ゆっくり食べる, 丁寧に書く. Include already-adverbial words such as ゆっくり so you practice noticing when conversion is unnecessary.
3. Use a three-column check. For each new adjective, record its dictionary form, its form before a noun, and its adverbial form. If you can produce きれい／きれいな部屋／きれいに掃除する, you are less likely to mistake きれい for an い-adjective.

Related Concepts

• Prerequisite: I-Adjectives — review how い-adjectives are identified and changed before learning their く form.
• Next step: Becoming なる/する — use adjective adverbial forms to express becoming a state or deliberately making something a certain way.