You use this to say you make something become a certain way. It shows you change something on purpose.
い-Adjective [stem] + く + するPrimary
You use this to say you make something become a certain way. It shows you change something on purpose.
部屋をもう少し暖かくしてください。
Please make the room a little warmer.
息子がテレビの音を大きくしたので、小さくした。
My son turned up the TV volume, so I turned it down.
話をそんなに難しくしないでください。
Please don't make the story so complicated.
髪を短くして、気分がさっぱりした。
I cut my hair short and felt refreshed.
この料理をもっと美味しくする方法を知っていますか？
Do you know a way to make this dish more delicious?
This is different from "~ku naru". "~ku naru" shows something changes by itself. This pattern shows you make something change. For example, you make a room warm. Also, this is for "i-adjectives". For "na-adjectives" and nouns, you use "~ni suru".
Watch out: You use 'を' with '〜く する'. This is because you are doing something to an object. For example, '音を小さくする' means 'I make the sound small'. Do not use 'が'. You use 'が' with '〜く なる'. This means something becomes small by itself. For example, '音が小さくなる' means 'The sound becomes small'.
Don't use this when you want to change a noun or a な-adjective. For example, you can't say "きれいにする" (kirei ni suru) with this rule. This rule is only for い-adjectives. You must remove the last "い" from the adjective. For "いい" (ii), which means "good", you must use "よく" (yoku). So, "to make better" is "よくする" (yoku suru). It's not "いくする" (iku suru).
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