This means 'to become' or 'to get' something. You use it when an 'i-adjective' changes into a new state. It shows something is changing.
い-Adjective [stem] + く なるPrimary
This means 'to become' or 'to get' something. You use it when an 'i-adjective' changes into a new state. It shows something is changing.
秋になると、日が短くなる。
When autumn comes, the days get shorter.
その映画を見て、とても悲しくなりました。
I watched that movie and became very sad.
この薬を飲んでも、頭痛は良くならない。
Even if I take this medicine, my headache doesn't get better.
空が暗くなってきたので、家に帰ろう。
The sky is getting dark, so let's go home.
今後、競争はさらに激しくなるものと予想されます。
It is predicted that competition will become even more intense from now on.
This grammar shows something changing by itself. You just notice it happening. It's like watching a flower bloom or the sky get dark. You don't make it happen. It just does.
This grammar is for い-adjectives. It means "to become" something. For な-adjectives and nouns, you use 〜に なる. For example, you say "samuku naru" (to become cold). But you say "genki ni naru" (to become healthy). 〜く なる shows a change that happens naturally. 〜く する means you make something change on purpose. For example, "heya o atatakaku suru" means "to make the room warm."
Watch out: The word for "good" is "ii" or "yoi". When you say "become good", you must use "yoku naru". Do not say "iku naru". When you say "not become good", you use "yoku nakunaru".
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