Adjectives with 〜く and 〜に: manner and change
Change an i-adjective to く and a na-adjective to に to describe how an action happens or how a state changes. Compare combinations with なる and する, and distinguish the noun-forming suffix さ.
Describe the manner of an action
文字を大きく書いてください。 uses 大きく to describe how the writing should be done. Replace the final い of an i-adjective with く.
子どもたちは元気に挨拶しました。 uses 元気に to describe how the children greeted someone. Add に to the stem of a na-adjective without including な.
Express change with なる and する
春になって、日が長くなりました。 describes the days becoming longer than before. Combine the く form of an i-adjective with なる to present a change of state.
会議の後、部屋が静かになりました。 means that the room became quiet after the meeting. When someone causes a change, forms such as 音を小さくする and 部屋をきれいにする can be used.
Distinguish the noun-forming suffix さ
山の高さを地図で確認しました。 uses 高さ as a noun referring to the mountain's height. Its role differs from 高く, which modifies an action or a change.
昨日より空が明るく見えます。 uses 明るく to modify 見えます, and the final verb carries the tense. Do not interpret く or に itself as a past-tense marker.
Quick check: Which sentence correctly says that the town became quiet: 町が静かなりました or 町が静かになりました?
Show the answer and why
町が静かになりました is correct. Add に to the na-adjective stem 静か and conjugate なる.