This lesson is about how you can create adverbs out of any adjective in Japanese.
To make an adjective an adverb, drop い and add く. For 形容動詞, you add に. These adverbs are normally translated with "-ly". However, for whenever English is weird and doesn't let us use -ly, we have to go with another translation.
| Adjective | Adverb | Adjective | Adverb | ||||
| 強い | Strong | 強く | Strongly | 静か（な） | Quiet | 静かに | Quietly |
| 弱い | Weak | 弱く | Weakly | かんたん（な） | Easy | かんたんに | Easily |
| 遅い | Late | 遅く | Late | まじめ（な） | Serious | まじめに | Seriously |
| 小さい | Small | 小さく | Small | きれい（な） | Pretty; nice | きれいに | Nicely |
Example Sentences
1. 簡単に説明する。
To easily explain.
2. 楽しく休日を過ごす。
To spend the holidays merrily.
3. 何かを小さく切る。
To cut something into small pieces.
4. わたしは毎日自分の部屋で一人静かに勉強します。
I study in my own room quietly every day.
5. インディゴで洗面台が青く染まった。
The washbasin was dyed blue with indigo.
6. あの（向こう）の電気が赤く輝いた。
That light over there shined red.
Phrase Note: あの is literally translated in English as "that over there" as it refers to something not directly near the speaker or listener. However, when the object of reference is truly literally "over there" as in on the other side of the speaker and listener, あの向こうの is more appropriate.
7. 姉は優しくなりました。
My older sister became nice.
Grammar Notes:
1. When we want to say that something "becomes X" but X is actually an adjectival attribute, we turn the adjective into an adverb and then add なる. So, "to become red" is 赤くなる. 赤くになる is wrong. However, you say きれいになる for "to become pretty". Remember that there are two classes of adjectives and that they always conjugate differently.
2. Continuing on 2, 信号が青くなった actually means "the light turned green". 青, not 緑, is the color used for streetlights for "green".
8. もう少し静かにしてください。
Please be more quiet
Grammar Note: The opposite of "(adjectival) adverb + なる" is "(Adjectival) adverb + する", which means "to make..." as in implementing a change.
9. 冬には太陽は早く沈む。
The sun sets early in the winter.
10. 深く息を吸う。
To take a deep breath.
確か VS 確かに
確か means "certain", but as an adverb, it's often paired with だろう・でしょう to mean "if I'm not mistaken". The other adverb form 確かに means "certainly". So, they're slightly different.
11. 世界の人口は、確か70億（人）ぐらいだ(った)と思います。
The population of the world, if I'm not mistaken is around 7 billion people.
12. 確かにその木が倒れるでしょう。
The tree will certainly fall.
13a. 確か（か）? (Very casual and a little blunt)
13b. 確かですか。
Is that for certain?
14. それは確かな証拠ではないです。
That is not definitive evidence.
Nuance Note: 多分 is less certain than 確か and きっと is more certain than 確かに.
Exceptional Phrases
Not all adverb phrases will be made similarly. For example, 必要に is not used. "Necessarily" is instead 必ず. Another example is けっこう. Although it too is a 形容動詞, it's adverbial form is just けっこう. Lastly, we have 少しく meaning "just a little". The word comes from when 少し was an adjective. It is occasionally used in the written language.
15. 今日はけっこう寒いです。
Today is quite cold.
16. 少しく思うところを述べる。(書き言葉)
To state a little bit of what you think.
Ends in に but not from 形容詞
Even though an adverb may end in に, this doesn't mean it necessarily comes from an adjective. Though this is usually the case, there are still very commonly used exceptions to this.
17. 現状は直ちに問題はありません。
There are no problems present right now.
18. レンタカーで直ちに空港を出発しました。
(I/we) immediately left the airport in a rental car.