Meaning & Usage
✨ Basic Meaning
“To make (something) [I-adjective],” or “to cause (something) to become [I-adjective].”
🎯 Primary Function
To express a transitive causative change, where the subject performs an action to change the state or quality of an object (marked by the particle を).
📋 Grammar Structure
I-Adjective Stem (drop い) + くする
I-Adjective Stem (drop い) + くする
Na-Adjective Stem + にする (Note: Use にする for Na-Adjectives)
I-Adjective Stem (drop い) + くしない
🎭 Usage Contexts
Formal Situations
Used in formal settings when the verb する is conjugated to its polite form (します) or a more formal structure.
Informal Situations
Used naturally in casual speech, often with the plain form (する) or past tense (した).
Written Language
Common in instructional materials, reports, and narratives to describe actions that lead to a resultant state.
Spoken Language
Very common in spoken Japanese for describing intentional changes and adjustments.
💡 Common Applications
Changing Physical States
Used when an action changes the temperature, size, volume, or other physical qualities of an object.
Example: 水を冷たくする (Mizu o tsumetaku suru)
Changing Abstract Qualities
Used to describe actions that alter abstract qualities like difficulty, clarity, or richness. *Note: For 簡単 (kantan), which is a Na-adjective, にする is used. For 難しい (muzukashii) -> 難しくする.*
Example: 問題を簡単くする (Mondai o kantan ni suru)
Expressing Intentional Action
Often appears with verbs of intent (like 〜たい, 〜つもり) as it expresses a transitive, deliberate change by the speaker or subject.
Example: 部屋をきれいにする (Heya o kirei ni suru)
Frequency
High
Difficulty
N4 / N3 Intermediate
Tag:
Example Sentences
Example #1
部屋を明るくするために、カーテンを開けます。
Furigana: へやをあかるくするために、カーテンをあけます。
Romaji: Heya o akaruku suru tame ni, kāten o akemasu.
English: I will make the room bright by opening the curtains.
Example #2
音を少し大きくしてください。
Furigana: おとをすこしおおきくしてください。
Romaji: Oto o sukoshi ōkiku shite kudasai.
English: Please make the volume a little louder.
Example #3
髪を短くしたいです。
Furigana: かみをみじかくしたいです。
Romaji: Kami o mijikaku shitai desu.
English: I want to make my hair shorter.
Example #4
彼女はスープを甘くしすぎた。
Furigana: かのじょはスープをあまくしすぎた。
Romaji: Kanojo wa sūpu o amaku shisugita.
English: She made the soup too salty.
Example #5
留学することで人生を豊かにすることができます。
Furigana: りゅうがくすることでじんせいをゆたかにすることができます。
Romaji: Ryūgaku suru koto de jinsei o yutaka ni suru koto ga dekimasu.
English: You can make your life richer by studying abroad.
Example #6
いつも私の仕事場所をきれいにしています。
Furigana: いつもわたしのしごとばしょをきれいにするようにしています。
Romaji: Itsumo watashi no shigotobasho o kirei ni shite imasu.
English: I try to keep my workspace clean at all times.
Example #7
説明を分かりやすくするために、イラストを使いました。
Furigana: せつめいをわかりやすくするために、イラストをつかいました。
Romaji: Setsumei o wakariyasuku suru tame ni, irasuto o tsukaimashita.
English: To make the explanation easier to understand, I used illustrations.
Example #8
天気予報は今晩、もっと寒くすると予想しました。
Furigana: てんきよほうはこんばん、もっとさむくするとよそうしました。
Romaji: Tenki yohō wa konban, motto samuku suru to yosō shimashita.
English: The weather report predicted that it would get colder tonight.
Example #9
食事を健康的にするために、もっと野菜を食べています。
Furigana: しょくじをけんこうてきにするために、もっとやさいをたべています。
Romaji: Shokuji o kenkōteki ni suru tame ni, motto yasai o tabete imasu.
English: I want to make my diet healthier, so I’m eating more vegetables.
Example #10
一枚に収めるため、フォントのサイズを小さくしてください。
Furigana: いちまいにおさめるため、フォントのサイズをちいさくしてください。
Romaji: Ichimai ni osameru tame, fonto no saizu o chiisaku shite kudasai.
English: Please make the font size smaller so it fits on one page.
Notes & Nuances
📌 Important Points
Requires the particle を (o) for the object.
The particle を (o) is crucial, as it marks the object that is being changed by the action of する. Without an object, the meaning shifts to “to become” (くなる).
Example: 机を低くする。 (Tsukue o hikuku suru.)
Used only for I-Adjectives.
This structure must be used exclusively with i-adjectives. For Nouns or Na-adjectives, the pattern changes to [Noun/Na-Adj] + にする.
Example: もっと速くしたい。 (Motto hayaku shitai.)
Conjugates like a standard verb (する).
Since する is a verb, it can be combined with other functional verbs (auxiliary verbs) such as 〜ておく (to do something in advance) or 〜てみる (to try doing).
Example: コーヒーを温かくしておきました。 (Kōhī o atatakaku shite okimashita.)
⚠️ Common Mistakes
❌ 間違って寒いにする。
✅ 寒いにする (Samui ni suru) -> 寒くする (Samuku suru)
I-adjectives must use the adverbial form ending in く before する. Na-adjectives use に. Mixing them is a common error.
❌ 音は大きくしました。
✅ 音が大きくなった (Oto ga ōkiku natta) -> 音を大きくした (Oto o ōkiku shita)
Confusing the transitive ‘くする’ (to make it big) with the intransitive ‘くなる’ (it became big). ‘くする’ requires an object (を).
🏛️ Cultural Context
Politeness Level: Neutral. The politeness level depends entirely on the conjugation of the verb する (e.g., します is polite, する is plain/informal).
Social Situations: Used widely across all social situations where describing a physical or qualitative change is necessary.
Regional Variations: Standard across all major dialects of Japanese.
🔍 Subtle Differences
〜くする vs. 〜くなる
くする is transitive (someone *makes* the change); くなる is intransitive (the subject *becomes* the change).
When to use: Use 〜くする when the subject actively causes the change. Use 〜くなる when the change happens naturally or without a stated agent.
〜くする (I-Adj) vs. 〜にする (Na-Adj/Noun)
The modifying particle differs based on the word type. く for I-adjectives, に for Na-adjectives/Nouns.
When to use: Use 〜くする when modifying I-adjectives (e.g., 寒い). Use 〜にする when modifying Na-adjectives (e.g., 静か) or Nouns (e.g., 医者).
📝 Conjugation Notes
The ‘くする’ form is derived from the i-adjective’s adverbial form (e.g., 早い -> 早く) followed by the verb する, which conjugates normally (します, した, しない, したい, etc.).
🔊 Pronunciation Tips
Ensure the ‘く’ sound is pronounced clearly and connected smoothly to ‘する.’ It sounds like one fluid phrase: ‘Adjective-ku-suru.’
🧠 Memory Tips
Think of the ‘く’ as a bridge connecting the adjective’s root meaning (e.g., ‘high’) to the action verb ‘する’ (to do/make). It transforms the adjective into an adverb, meaning ‘in a [state] way.’
Other Grammar
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