Meaning & Usage
✨ Basic Meaning
“To make something become [adjective/noun]” or “to cause something to be [adjective/noun]”. It expresses bringing about a change in state or condition of an object or person.
🎯 Primary Function
To describe a transitive action where the subject causes a change in the state or condition of the object.
📋 Grammar Structure
Verb (transitive) + Object (を) + i-adjective(-い) + く + する
Verb (transitive) + Object (を) + na-adjective(-な) + に + する
Verb (transitive) + Object (を) + Noun + に + する
🎭 Usage Contexts
Formal Situations
Used commonly in formal and polite speech and writing, often with the ます form of する (します).
Informal Situations
Used frequently in casual conversations.
Written Language
Appears in various forms of written Japanese, including articles, reports, and casual writing.
Spoken Language
Widely used in everyday spoken Japanese.
💡 Common Applications
Making things bigger/smaller/longer/shorter, etc.
Used with i-adjectives describing size, length, or other physical properties.
Example: 部屋を広くしました。(Heya o hiroku shimashita.) – I made the room spacious.
Making things clean/simple/pretty, etc.
Used with na-adjectives describing state, appearance, or complexity.
Example: 部屋をきれいにします。(Heya o kirei ni shimasu.) – I will make the room clean.
Making something into something else.
Used with nouns to express changing something into a different object or role.
Example: 水を氷にします。(Mizu o koori ni shimasu.) – I will make water into ice.
Frequency
Very common and essential for expressing transitive changes in state.
Difficulty
Intermediate (N4). The main challenge is remembering which particle (く or に) to use based on the preceding word type.
Example Sentences
部屋を明るくしてください。
Please make the room bright.
髪を短く切りました。
I cut my hair short (made my hair short).
道をきれいに掃除しました。
I cleaned the road beautifully (made the road clean).
Notes & Nuances
📌 Important Points
Particle choice depends on the word type.
Use く after i-adjectives (removing い), and に after na-adjectives (removing な) and nouns.
Example: 大きい → 大きくする
静か(な) → 静かにする
先生 → 先生にする
する means “to make” or “to cause a change”.
In this pattern, する acts as a transitive verb, indicating that the subject is actively causing the state change of the object.
Example: 水を冷たくします。(Mizu o tsumetaku shimasu.) – I make the water cold.
⚠️ Common Mistakes
❌ Using に with i-adjectives.
✅ i-adjectives require く.
Incorrect: 部屋をきれいにしました。(Incorrect particle for i-adjective)
Correct: 部屋をきれいにしました。(Correct usage with na-adjective きれいな)
❌ Using く with na-adjectives or nouns.
✅ na-adjectives and nouns require に.
Incorrect: 会議の時間を九時くしました。(Incorrect particle for noun)
Correct: 会議の時間を九時にしました。(Correct usage with noun 九時)
🏛️ Cultural Context
Politeness Level: Neutral; politeness is conveyed through the conjugation of する (します, etc.) and overall sentence structure.
Social Situations: Applicable in a wide range of social contexts, from casual requests to formal instructions.
Regional Variations: No significant regional variations in the use of くする / にする.
🔍 Subtle Differences
~くする / ~にする vs ~くなる / ~になる
~くする / ~にする are transitive (Subject makes Object change). ~くなる / ~になる are intransitive (Subject itself changes).
When to use: Use ~くする / ~にする when you are causing the change. Use ~くなる / ~になる when something naturally or incidentally changes on its own or due to an external force not directly caused by the subject.
〜にする vs 〜にきめる (~ni kimeru)
〜にする means “to make (it) into…” or “to decide on…” (often a choice from options). 〜にきめる means “to decide (to do something)” or “to decide on (a specific course of action/item)”.
When to use: Use 〜にする when stating what you decided *on* or *to turn something into*. Use 〜にきめる when stating the decision itself or the action decided upon.
Adverbial form + Verb vs ~くする/~にする
Adverbial form + Verb modifies *how* the action is performed. ~くする/~にする modifies *what* the object becomes.
When to use: Example: 早く歩く (hayaku aruku – walk quickly) – modifies how you walk. 時間を早くする (jikan o hayaku suru – make the time earlier) – changes the time itself.
📝 Conjugation Notes
The する part conjugates like a regular verb (します, しました, して, しない, しよう, etc.).
🔊 Pronunciation Tips
Pay attention to the slight pause or connection between く/に and する. Pronunciation is generally straightforward.
🧠 Memory Tips
Remember “い**く** に**な** Noun**に**”. Associate い-adjectives with く and な-adjectives/Nouns with に.
Practice Exercises
部屋を（ ）したいです。 (きれい)
きれいく
きれいにする
きれいなする
きれいにする
髪を（ ）切りました。 (長い)
長く
長いに
長いする
長くな
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