This lesson is about how you can get adverbs out of any adjective in Japanese. It'll be easy!
To make an adjective an adverb, you use the 連用形. All this term means is that it shows a continuation of a phrase, and because adverbs are extensions of a verb phrase, the term makes a lot of sense. We have two classes of adjectives, so they still look different when turned into adverbs.
The 連用形 of 形容詞 ends in く. So, all you do is drop い and add く. For 形容動詞, we have use the 連用形 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.
To easily explain.
To spend the holidays merrily.
To cut something into small pieces.
I study in my own room quietly every day.
The washbasin was dyed blue with indigo.
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.
My older sister became nice.
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".
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.
The sun sets early in the winter.
To take a deep breath.
Practice (1): Translate the following.
2. It became large.
4. Please clean up your room.
*Etymology Note: If you think the に above looks like a particle, you're intuition is right.The other 連用形 of 形容動詞, で, is a particle as well. The copula comes from a combination of に and the verb for existence, ある. We get だ from である. You may be wondering why we don't get にある, but that was used in older Japanese. The particle て got added to the phrase and caused a contraction to give us the で. Thus, we have grounds for に and で showing up here. For the adverb use of the 連用形, we use に. When we connect phrases together--remember the て形--we use で. This also means that the 連用形 of 形容詞can be used to connect phrases just like て, but this is used in formal speech and writing. So, we'll see that later on.
Part of Speech Note: The process discussed in this lesson is not the only way to make adjectives into adverbs. There are other endings that can be used to make adverbs, but they will be discussed later on.
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.
The population of the world, if I'm not mistaken is around 7 billion people.
Grammar Note: Notice the absence of the counter ～人. This acceptable in contexts like this. The key word is "population". It is also important to note that "if I'm not mistaken" may be more literally said asもし私が間違っていなければ. However, this phrase has grammar regarding conditional phrase which we have not gone over yet. So, you may put off on learning this phrase for later.
The tree will certainly fall.
13a. 確か（か）? (Very casual and a little blunt)
Is that for certain?
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.
Depending on context, よく either means "well" or "often". The deciding factors include where it is placed in the sentence and what verb it is used with. When よく is closer to the start of a sentence, it is normally interpreted as "well". Context also helps.
Please listen carefully/well.
To go to Tokyo often/frequently.
"Do you come to Japan often?" "No, I don't come very often".
To go to Tokyo nicely.
Word Note: 問題, here, is not problem as in question, which would be 質問.
Practice (2): Translate the following. You may use a dictionary.
1. I know him well.
2. They play a lot/often.
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.
Today is quite cold.
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.
There are no problems present right now.
(I/we) immediately left the airport in a rental car.
Adverbs from Doubling Verb/Adjective Roots
There are actually a handful of adverbs made this way. Examples include 高々（と） (very high/at most), 軽々（と） (easily/lightly), 飛び飛び（に） (scattered here and there), and 代わる代わる (alternately).
There also rarer ones from the doubling of the 終止形 of verbs such as 泣く泣く (in tears; reluctantly). Note that the と & に in these adverb phrases are not grammatically necessary but are common.
We hoisted the flag high.
1. To cut the explanation short.
3. Please make it cheaper.
5. To have one's hair long.
3. To closely look at the problem; to look at the problem well.
4. Are there often earthquakes?
5. To often eat instant food.
6. To drink a lot.
7. Well done.
8. Please consider it well.