くする
Attached to an い-adjective, くする means "to make something (adjective)". It describes someone deliberately changing a thing into the state the adjective expresses.
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A neutral, everyday pattern for adjusting things, such as lights, hair, temperature or volume. It often appears with たい (〜くしたい) or in requests (〜くしてください). It focuses on a person causing the change. くなる, by contrast, describes a change that simply happens.
Do not attach くする to な-adjectives or nouns; use にする instead (静かにする, not 静かくする).
Learners sometimes say いくする for いい; the correct form is よくする.
Note that くする needs an object marked with を, because someone is doing the changing.
- なるN5「なる」 is intransitive: it only says what the subject itself becomes, not who brought it about, and besides い-adjectives (くなる) it also attaches to な-adjectives and nouns (になる) and to the verb ない-form (なくなる). It is not interchangeable with 「くする」.
- にするN5「にする」 attaches to nouns and な-adjective stems (e.g. 「静かにする」), while 「くする」 takes only い-adjectives, so the two divide the work by word class and are not interchangeable. 「にする」 can also express choosing or deciding (e.g. 「お茶にします」), which 「くする」 cannot.
- ようにするN4「ようにする」 follows a verb's dictionary, ない-, or potential form and means making an effort to do (or not do) something, or trying to bring about a state; 「くする」 attaches to い-adjectives and directly changes the target into that state. Because they connect to different forms, they are not interchangeable.
- ようになるN4「ようになる」 follows a verb's dictionary, potential, or ない-form and describes abilities or habits changing naturally over time, without stressing intention; 「くする」 attaches to い-adjectives and expresses a person changing the target's state. Because they connect to different forms, they are not interchangeable.
- させるN4「くする」 attaches to い-adjectives and expresses someone changing the state of a person or thing; 「させる」 attaches to verbs and means forcing or allowing someone to do an action, and it can also make someone feel an emotion. Because they connect to different forms, they are not interchangeable.
くする (い-adjective) and にする (な-adjective/noun) describe someone making a change, while なる describes a change that happens by itself. ようにする (make sure to do / try to do) and ようになる (come to be / come to be able to) attach to verbs rather than adjectives, and させる is the causative meaning "make or let someone do" an action.
