Becoming with なる and する in Japanese

In Brief

Use なる when someone or something enters a new state: 暖かくなる “become warm” and 医者になる “become a doctor.” Use する when someone actively creates or chooses that state: 部屋を暖かくする “make the room warm” and コーヒーにする “choose coffee.” Before either verb, an い-adjective changes to 〜く, while a な-adjective or noun takes に.

Overview

Japanese commonly describes change by combining a state word with なる or する. なる means roughly “become,” “get,” or “come to be.” It presents the change as something that happens to the person or thing concerned. する means “make,” “set,” or, in choice expressions, “decide on.” It presents someone as bringing the result about deliberately or selecting it.

This A2 pattern is especially useful because English does not package these ideas in one consistent way. English may say “get cold,” “become a doctor,” “make it cheaper,” or “have the coffee.” Japanese builds all four around the same small set of patterns. Once you know how adjectives work as adverbs—forms such as 速く and 静かに—the formation is regular.

A noun is a word for a person, thing, role, or category, such as 医者 “doctor.” Japanese adjectives belong mainly to two groups: い-adjectives, whose dictionary form normally ends in い, and な-adjectives, which take な before a noun. This distinction determines whether the form before なる or する ends in く or に.

How It Works

The beginner rule

Word type	Basic state	With なる	With する
い-adjective	暖かい (warm)	暖かくなる (become warm)	暖かくする (make warm)
な-adjective	静かだ (quiet)	静かになる (become quiet)	静かにする (make quiet)
Noun	医者だ (a doctor)	医者になる (become a doctor)	医者にする (make/appoint someone a doctor; choose a doctor, depending on context)

The practical formulas are:

• い-adjective: remove final い, then add くなる or くする
• な-adjective: use the adjective stem, without な or だ, then add になる or にする
• noun: add になる or にする

The word immediately before なる or する describes the resulting state, not the starting state. In 部屋が暖かくなりました, the room ended up warm. In 部屋を暖かくしました, someone made warmth the room’s resulting condition.

なる: a change happens

With なる, the person or thing changing is commonly marked by が or presented as the sentence topic with は. A topic is what the sentence is about; は marks it. There is normally no direct object because なる is intransitive—that is, the change happens to its subject rather than being done directly to an object.

• 天気が暖かくなりました。 — The weather became warmer.
• 町は静かになりました。 — The town became quiet.
• 姉は医者になりました。 — My older sister became a doctor.

なる itself conjugates as a regular godan verb:

Form	Japanese	Typical meaning
Non-past	なる / なります	becomes; will become
Past	なった / なりました	became; has become
Negative	ならない / なりません	does not/will not become
Past negative	ならなかった / なりませんでした	did not become
て-form	なって	becoming; become and…
Desire	なりたい	want to become

Japanese non-past forms can refer to a future change. 来年、大学生になります naturally means “I’ll become a university student next year.” To describe a completed change, use なった or polite なりました.

する: someone creates a state

With する, the person or thing being changed is usually the direct object—the person or thing directly affected by an action—and takes を.

• 部屋を暖かくしました。 — I made the room warm.
• 音を小さくしてください。 — Please turn the sound down.
• 机をきれいにしました。 — I made/left the desk clean.

Compare the particle and the viewpoint:

Japanese	English	Viewpoint
部屋が明るくなりました。	The room became bright.	The room underwent a change.
部屋を明るくしました。	I made the room bright.	Someone caused the change.
子どもが静かになりました。	The child became quiet.	Change in the child’s state.
子どもを静かにしました。	I quieted the child.	Someone brought about that state.

English often leaves the cause implicit: “The room got brighter” may still suggest that someone turned on a light. Japanese makes you choose whether to frame the event as a change with なる or as an action on something with する.

にする when choosing

Noun + にする also means “choose,” “decide on,” or “settle for.” In a restaurant, コーヒーにします is not usually “I will make something into coffee.” It means “I’ll have coffee” or “I’ll go with coffee.” The options may be stated with は:

• 飲み物はお茶にします。 — For my drink, I’ll have tea.
• 会議は金曜日にしましょう。 — Let’s set the meeting for Friday.
• この色にします。 — I’ll choose this color.

Context tells you whether noun + にする means selecting an option, assigning a role, or transforming something. 彼をリーダーにしました means “We made/appointed him leader,” while 私は田中さんをリーダーにしました makes the person choosing explicit.

The irregular adjective いい

The common adjective いい “good” uses the older stem よ- when it changes form. Therefore:

• よくなる — become better
• よくする — improve something; make something better
• not いいくなる or いいくする

The same applies to compounds ending in いい, such as かっこいい → かっこよくなる “become good-looking/cooler.”

Examples in Context

Japanese	English	Note
春になって、暖かくなりました。	Spring arrived, and it became warm.	い-adjective + くなる
この町は十年前より便利になりました。	This town has become more convenient than it was ten years ago.	な-adjective + になる
弟は来年、高校生になります。	My younger brother will become a high school student next year.	Noun + になる; future meaning
子どものころから医者になりたいです。	I have wanted to become a doctor since childhood.	なる in the desire form
毎日練習すれば、もっと上手になります。	If you practise every day, you will get better at it.	A gradual improvement
暗くなったので、電気をつけました。	It got dark, so I turned on the light.	Past なる links naturally to a reason
風邪はよくなりましたか。	Has your cold got better?	Irregular いい → よく
エアコンで部屋を涼しくしました。	I made the room cool with the air conditioner.	Object + い-adjective + くする
もう少し字を大きくしてください。	Please make the letters a little larger.	A polite request for adjustment
音楽を静かにしてください。	Please make the music quieter.	Object + な-adjective + にする
私たちは田中さんを代表にしました。	We made Ms. Tanaka our representative.	Person + を; role + にする
部屋をきれいにしてから、友達を呼びました。	I cleaned the room before inviting my friends over.	きれいにする often means “clean/tidy”
デザートはアイスクリームにします。	I’ll have ice cream for dessert.	Choosing from options
次の旅行先は京都にしませんか。	Why don’t we choose Kyoto for our next trip?	Negative question as a suggestion
会議の時間を三時にしました。	We set the meeting time for three o’clock.	Setting a time to a chosen value

Notice that translations do not always contain “become” or “make.” Natural English says “get better,” “turn the sound down,” “clean the room,” or “set the time.” Learn the Japanese pattern by its function rather than by forcing one English verb into every translation.

Common Mistakes

Keeping い on an い-adjective

• Wrong: 寒いになりました。
• Right: 寒くなりました。
• Why: Before なる, an い-adjective loses final い and takes く. に belongs to nouns and な-adjectives, not ordinary い-adjectives.

Adding な before なる or する

• Wrong: 部屋が静かななりました。
• Right: 部屋が静かになりました。
• Why: The な in 静かな部屋 connects a な-adjective to a noun. Before なる or する, use 静かに, without な.

Using だ in the result phrase

• Wrong: 先生だになりました。
• Right: 先生になりました。
• Why: A noun takes に directly before なる or する. The copula だ—the linking word in statements such as 先生だ “is a teacher”—does not remain here.

Mixing up が and を

• Wrong: 部屋を暖かくなりました。
• Right: 部屋が暖かくなりました。 — The room became warm.
• Also right: 部屋を暖かくしました。 — I made the room warm.
• Why: The thing undergoing a change takes が with なる. The thing someone actively changes takes を with する.

Treating いい as regular

• Wrong: 薬を飲んで、いいくなりました。
• Right: 薬を飲んで、よくなりました。
• Why: いい changes with the stem よ-, giving よくなる.

Translating “I’ll have…” word for word

• Unnatural for choosing: コーヒーを持ちます。
• Natural: コーヒーにします。
• Why: When selecting from a menu or set of options, Japanese commonly uses noun + にする. 持つ means physically hold, possess, or carry, not order a drink.

Usage Notes

Change versus deliberate action

The なる/する contrast is often taught as “natural change versus deliberate change.” That is a helpful first rule, but “natural” does not mean “without a cause.” If someone turns up the heating, 部屋が暖かくなりました is still possible: it simply focuses on the room’s resulting change. 部屋を暖かくしました focuses on the person’s action of warming it.

Likewise, する does not always imply force. In 髪を短くしました “I had my hair cut short,” the speaker intentionally chose the result, even if a hairdresser performed the physical action.

Context often supplies the subject

Japanese frequently omits information that is already clear. 静かになりました may mean “It became quiet,” “He became quiet,” or “The neighborhood became quiet,” depending on the conversation. コーヒーにします normally omits 私は because the speaker’s choice is obvious.

Politeness comes from the verb ending

The pattern itself is neutral. Use なります／します in polite conversation and なる／する in casual conversation or plain-form grammar. Requests normally use 〜くしてください or 〜にしてください:

• 少し安くしてください。 — Please make it a little cheaper.
• 飲み物は水にしてください。 — Please make the drink water / Please give me water instead.

The second sentence can sound like a request to arrange something, while 水にします states the speaker’s own choice.

Beyond the Basics: Forms You Will Meet Later

You do not need to master all of the following at A2, but they grow directly from the same idea of entering or choosing a state.

〜ようになる: a new ability or habit develops

A verb before ようになる describes a change in ability, habit, or circumstances:

• 日本語が話せるようになりました。 — I became able to speak Japanese.
• 毎朝、早く起きるようになりました。 — I started getting up early every morning.

Do not attach plain なる directly to a verb: 話せるになる is incorrect. The linking expression ように is required. With ようにする, the focus changes to a conscious effort or policy:

• 毎日、日本語を読むようにしています。 — I make a point of reading Japanese every day.

〜ことになる and 〜ことにする: decisions

With a verb clause (a group of words built around a verb), こと turns the action into a “matter” that can be decided.

Japanese	English	Main viewpoint
来月、東京へ行くことになりました。	It has been decided that I will go to Tokyo next month.	The decision is presented as arranged by circumstances or others.
来月、東京へ行くことにしました。	I decided to go to Tokyo next month.	The speaker presents it as their own decision.

This parallels the basic contrast: なる presents an outcome that comes about, while する presents an intentional choice.

〜くしている and 〜にしている: maintaining a state

The progressive form of する can mean keeping something in a chosen condition:

• 部屋を暖かくしています。 — I keep the room warm.
• 机の上をきれいにしています。 — I keep the top of my desk tidy.

By contrast, 暖かくなっています describes a current change or resulting condition, depending on context: “It is getting warm” or “It has become warm.”

となる and とする in formal language

Formal announcements, reports, and written descriptions sometimes use と where everyday language often uses に:

• 新しい制度は四月から実施となります。 — The new system will take effect from April.
• 参加費は一人千円とします。 — The participation fee shall be 1,000 yen per person.

となる can sound more formal, categorical, or focused on a notable outcome than になる. It is not a simple interchangeable upgrade for every everyday sentence. Beginners should continue to use に patterns unless they are learning a fixed formal expression.

Practice Tips

1. Build contrast pairs. Choose five states and say one sentence with なる and one with する: 音が小さくなる／音を小さくする. This trains both the verb choice and the が/を contrast.
2. Sort words before forming sentences. Label each new adjective as い or な. Then produce its change form immediately: 高い → 高くなる, 元気 → 元気になる. Keep いい → よくなる as a special flashcard.
3. Use real choices. At meals or while shopping, silently choose with 〜にします: 今日は魚にします, 青いのにします. Connecting the pattern to genuine decisions makes it easier to recall than memorizing a translation alone.

Related Concepts

• Prerequisite: Adjectives as Adverbs — explains why い-adjectives use 〜く and な-adjectives use 〜に before verbs.