This difference between なる and する is derived from the characteristics of Japanese transitive and intransitive verbs. なる is an intransitive verb focusing on the “change” and する is a transitive verb focusing on the “doer.” This might help you remember the difference!
Japanese Articles
“To become”: How to express change in Japanese?
By: Masaru Mito Wed Jun 10 2026
JapaneseVerbs
The most basic way to express change in Japanese is to use the verb なる[naru](to become). But did you know that the verb する[suru](to do) can also be used to discuss changes? More than that, both of these verbs also have can be used alongside よう[yō] and こと[koto] to form longer expressions that we use to discuss changes in behavior or habits.
Japanese expressions for discussing change | |
|---|---|
なる naru | ようになる yō ni naru |
ことになる koto ni naru | |
する suru | ようにする yō ni suru |
ことにする koto ni suru | |
So what’s the difference between these different expressions? Luckily there are some simple rules you can follow!
In this post we’ll first look at the difference between なる[naru] and する[suru], and how they’re used to discuss becoming. Then we’ll look at these longer expressions and how to use each of these basic verbs with よう[yō] vs. こと[koto]. Let's get to it!
Verbs of change: なる [naru] vs. する [suru]
In Japanese, you can express that something has changed using either なる[naru], a u-verb, or する[suru], an verb. There is one major difference between the two:
なる[naru] indicates a change beyond anyone’s control, it’s an accidental or natural change.
今日は暑いですけど、明日は涼しくなるでしょう 。
Kyō wa atsui desu kedo, ashita wa suzusiku narudeshō.
It’s hot today, but it will probably become cool tomorrow.
→ a natural changeする[suru] indicates a change that was intentional, someone caused or underwent a change on purpose.
今日は暑いから、クーラーをつけて、部屋を涼しくし ましょう。
Kyō wa atsui kara, kūrā o tsukete, heya o suzusiku shimashō.
It’s hot today, so let’s turn on the AC and make the room (become) cool.
→ an intentional change
Did you know?
How to describe the end result of a change with なる and する?
When you want to say that something has changed in Japanese, you’ll often use なる[naru] and する[suru] alongside a word or phrase that describes either the end result of the change. That might be an (e.g. “became tall”) or a (e.g. “became a teacher”).
The end result is an i-adjective
When you use なる[naru] or する[suru] before an i-adjective, the final い[i] of the adjective will change into く[ku].
i-adjective
なる / する
おもしろい
omoshiroi
interesting
→
おもしろく なる
omoshiroku naru
becomes interesting
おもしろい
omoshiroi
interesting
→
おもしろく する
omoshiroku suru
make interesting
For example:
日本語の勉強は、最初は大変でしたけど、今は楽しくなりました。
Nihongo no benkyō wa, saisho wa taihen deshita kedo, ima wa tanoshiku narimashita.
Studying Japanese was hard at first, but now it has become fun.
Exception!
いい[ii](good) becomes よく[yoku] before なる or する. It’s similar to the rule for forming the negative form of this verb: よくない[yokunai].
昨日は頭が痛かったけど、今日はよくなりました。
Kinō wa atama ga itakatta kedo, kyō wa yoku narimashita.
I had a headache yesterday, but I got better today.
The end result is a noun or a na-adjective
When the end result of a change is a na-adjective or a noun, add に[ni] between the dictionary form and なる or する.
na-adjective
なる / する
きれい
kirei
clean
→
きれい に なる
kirei ni naru
become clean
きれい
kirei
clean
→
きれい に する
kirei ni suru
make clean
noun
なる / する
先生
sensei
teacher
→
先生 に なる
sensei ni naru
become a teacher
先生
sensei
teacher
→
先生 に する
sensei ni suru
make (someone) a teacher
Here are some examples of how to use these in sentences:
- na-adjectiveに [ni]する [suru]
スマートフォンは、私たちの生活を 便利にしました。
Sumātofon wa, watashitachi no seikatsu o benri ni shimashita.
Smartphones made our lives more convenient.
- nounに [ni]なる [naru]
将来、 プログラマーになりたいです。
Shōrai, purogramā ni naritai desu.
I want to become a programmer in the future.
The end result is a negative noun or adjective
The end result of a change, in Japanese, can also be a negative adjective or a negative noun. You might use this to say that something became “impossible” (not possible) or someone became a “non-emergency” (not an emergency).
You may recall that the form of an adjective or noun will end with ない[nai]. When this ending comes before なる or する, ない[nai] will become なく[naku]. Have a look!
i-adjective | na-adjective | Noun | |
|---|---|---|---|
Dictionary form | むずかしい muzukashii difficult | べんり benri convenient | ファン fan fan (as in fanatic) |
Negative Form | むずかしくない muzukashiku nai not difficult | べんりじゃない benri ja nai not convenient | ファンじゃない fan ja nai not a fan |
With なる | むずかしくなくなる muzukashiku nakunaru become not difficult | べんりじゃなくなる benri ja nakunaru become not convenient | ファンじゃなくなる fan ja nakunaru become a non-fan |
With する | むずかしくなく する muzukashiku nakusuru make not difficult | べんりじゃなくする benri ja nakusuru make not convenient | ファンじゃなくする fan ja nakusuru make into a non-fan |
Have a look at how you might use these expressions in a sentence:
- i-adjective basenegativeなる [naru]
このドラマは、シーズン１は面白かったけど、その後は面白くなくなりました。
Kono dorama wa, sīzun ichi wa omoshirokatta kedo, sono ato wa omoshiroku nakunarimashita.
Season 1 of this drama was interesting, but after that it became not interesting.
- na-adjective basenegativeなる [naru]
あの町は、若い人が少なくなってから、にぎやかじゃなくなりました。
Ano machi wa, wakai hito ga sukunaku natte kara, nigiyaka ja nakunarimashita.
That town has become less lively since the number of young people decreased.
- nounnegativeなる [naru]
前はこの歌手の大ファンでしたけど、今はファンじゃなくなりました。
Mae wa kono kashu no dai fan deshita kedo, ima wa fan ja nakunarimashita.
I used to be a big fan of this singer, but I became a non-fan.
Tip
In Japanese we often avoid saying that something a became a negative word if there is a normal, non-negative word with the same meaning. It’s like how, in English, you would choose to say that something “got old” rather than saying it “got not new.”
- affirmative adjective
✅難しいルールは、ゲームを つまらなくすると思う。
Muzukashii rūru wa, gēmu o tsumaranaku suru to omou.
I think complicated rules make games boring.
negative adjective🆗 難しいルールは、ゲームを おもしろくなくすると思う。
Muzukashii rūru wa, gēmu o omoshiroku naku suru to omou.
I think complicated rules make games not interesting.
→ This is acceptable, but unnecessarily complicated and hard to say!
よう [yō] vs. こと [koto]: Changes in behavior
In Japanese, we also often use なる[naru] and する[suru] alongside the words よう[yō] and こと[koto] to describe changes in behavior. We do this using by following the pattern below:
Verb (plain)
new behavior
よう / こと
yō / koto
に
ni
なる / する
naru / suru
When should you use よう[yō] and when should you use こと[koto]?
よう[yō] focuses on the process, indicating a gradual change in behavior.
こと[koto] indicates that someone decided the change should happen.
There are four possible combinations of よう[yō], こと[koto], なる[naru], and する[suru]. Here’s a quick summary of when you should use each of these expressions to describe a change in behavior:
なる[naru] accidental change | する[suru] intentional change | |
|---|---|---|
よう[yō] gradual change | ようになる yō ni naru a gradual, natural, unintentional change in behavior → a “drifting” change | ようにする yō ni suru an intentional, gradual change in behavior → a project or effortful change |
こと[koto] decisive change | ことになる koto ni naru a forced, required, or mandated change in behavior → a response to instructions | ことにする koto ni suru a decision to change one’s own behavior → a resolution |
Now let’s look at some examples of each expression and discuss why you’d use each expression for each purpose.
ようになる [yō ni naru]: Natural, unintentional change
We use ようになる[yō ni naru] after the plain form of a verb to indicate a change in behavior that is outside anyone’s control. You might use this to describe a gradual change in habit, or a natural change in behavior or abilities as someone matures.
verb (plain)ようになる [yō ni naru]私の娘は、２歳になってから、 話すようになりました。
Watashi no musume wa, ni sai ni natte kara, hanasu yō ni narimashita.
My daughter started talking after she turned two.
If you recall the functions of よう[yō] and なる[naru], this should make sense to you: よう is used for a gradual change and なる is used when the subject does not have control over the change.
Important
The pattern above describes a change in habit, but if you change the form of the verb for the new behavior, you can use the pattern to describe a change in ability instead. To do this you need to use the potential form of the verb instead.
Verb (potential)
new abilityようになる
yō ni naru
=natural change in ability
前は野菜を食べられなかったけど、今は 食べられるようになりました。
Mae wa yasai o taberarenakatta kedo, ima wa taberareru yō ni narimashita.
I couldn’t eat vegetables before, but now I can.
→ I couldn’t eat vegetables before, but now I became able to eat (them).If you use the plain form, though, you are simply describing a change in habit, not capability:
verb (plain)ようになる [yō ni naru]前は野菜を食べなかったけど、 今は食べるようになりました。
Mae wa yasai o tabenakatta kedo, ima wa taberu yō ni narimashita.
I didn’t use to eat vegetables, but now I do.
You’ll often her the potential form used with ようになる, especially when the speaker describes a change in themselves.
Tip
Some Japanese verbs express natural change all by themselves. You shouldn’t use the pattern above when you use these verbs.
✅最近ちょっと太りました。
Saikin chotto futorimashita.
I gained a little weight recently.
❌最近ちょっと太るようになりました
Saikin chotto futoru yō ni narimashita.
Here are a few common verbs of change, like this:
太る
futoru
gain weight
痩せる
yaseru
lose weight
伸びる
nobiru
extend
縮む
chijimu
shrink
増える
fueru
increasse
減る
heru
decrease
慣れる
nareru
get used to
ようにする [yō ni suru]: Intentional, effortful change
You can use the plain form of a verb before ようにする[yō ni suru], to describe an intentional, often effortful, change in the subject’s own habits or behavior.
verb (plain)ようにする [yō ni suru]健康のために、毎日 走るようにしました。
Kenkō no tame ni, mainichi hashiru yō ni shimashita.
For my health, I made an effort to run every day.
→ I worked to change my own behavior.This is because よう[yō] is used for a gradual change and する[suru] indicates that the subject has control over it.
ことになる [koto ni naru]: Changing someone else’s behavior
We use the plain form of a verb before ことになる[koto ni naru] when someone makes the decision that someone else’s behavior will change. For example:
verb (plain)ことになる [koto ni naru]部長に言われて、週末も会社に 行くことになりました。
Buchō ni iwarete, shūmatsu mo kaisya ni iku koto ni narimashita.
My boss told me, I will start going to the office on the weekend too.
→ Someone else (my boss) made a decision that my behavior will change.This results from こと used for a decision and なる indicating that the subject isn’t in control of it.
ことにする [koto ni suru]: Deciding to make change
Lastly, when ことにする[koto ni suru] follows a plain verb, that indicates the subject’s decision to change their own behavior. This is because こと[koto] is used when a decision is made and する[suru] is used when the change is under the subject’s control.
verbことにする [koto ni suru]夏休み、旅行に行くことにしました。
Natsuyasumi, ryokō ni iku koto ni shimashita.
I have decided to go on a trip during summer break.
Tip
In some situations, you may use ことになる[koto ni naru] rather than ことにする[koto ni suru], even though you are the one making the plan. Why? Because it can make you sound more polite or deferential: it’s not you deciding to behave a certain way, it’s an obligation. For example:
Speaker A:明日買い物に行きませんか。
Ashita kaimono ni ikimasenka.
Do you want to go shopping tomorrow?
Speaker B:すみません、 明日は友達に会うことになっているんです。
Sumimasen, ashita wa tomodachi ni au koto ni natteiru ndesu.
Sorry, I’m supposed to meet up with my friends tomorrow.
→ Speaker B probably isn’t being forced to meet up with their friends tomorrow, but it sounds less like a rejection to state it like an obligation.Important
With any of the patterns above, you can indicate that the changed behavior has become a habit by putting the verb なる[naru] or する[suru] into the ている[te iru]form .
ている [te iru] form私の会社では、9時までに会社に来ることになっています 。
Watashi no kaisha dewa, kuji madeni kaisha ni kuru koto ni natteimasu.
In my company, it is a rule to come to work by 9 a.m.
lit. At some point, the boss decided to change our behavior, so that we would come in by 9, so doing so is a habit: a rule we all follow.
Negation when なる and する describe a change in behavior
There are three ways to negate sentences that use なる[naru] or する[suru] to describe change in behavior. The pattern you follow, though, will depend on exactly what you want to express. Let’s check them out!
Stopping an action
To say that someone stops doing something, put the plain verb for the stopped action into its plain negative form, then use なる[naru] or する[suru] directly after it. You don’t need よ[yō] or こと[koto] here!
Verb (plain, negative)
stopped actionなる／する
naru / suru
昔はロックをよく聞きましたけど、今は聞かなくなりました。
Mukashi wa rokku o yoku kikimashita kedo, ima wa kikanaku narimashita.
I used to listen to rock music, but don’t listen to it anymore.
→ Notice that the usual negative ending ない[nai] becomes なく[naku] before the verb of change, just like we saw above!Important
You can describe an action that stops using the plain negative form before ように[yō ni] as well.
plain verb (negative)ように [yō ni]なる [naru]パソコンが 使えないように なりました。
Pasokon ga tsukaenai yō ni narimashita.
My computer became unusable.
→ Notice that the negative ending ない[nai] doesn’t change!However, you shouldn’t use ように[ yō ni] if something stops suddenly.
adverbように [yō ni]❌ パソコンが 急に使えない ようになりました。
Pasokon ga kyū ni tsukaenai yō ni narimashita.
Intended meaning: My computer suddenly became unusable.
Decision to stop an action
If you include こと[koto] after a negated plain verb, you will either be talking about a decision to stop doing something.
Verb (plain, negative)
stopped actionことに
koto ni
なる／する
naru / suru
仕事が忙しいから、パーティに 行かないことに しました 。
Shigoto ga isogashii kara, pātī ni ikanai koto ni shimashita.
Since I’m busy at work. I have decided not to go to the party.
→ Notice we don’t need to change the ない[nai] ending here!No change in behavior
When you want to express that no change in behavior took place, then なる[naru] or する[suru] will be negated instead. You might use this to say something failed to change or stayed the same.
verb (plain)なる [naru]１年間英語を勉強したけど、上手に話せるようになりませんでした。
Ichinenkan ēgo o benkyō shita kedo, jōzu ni hanaseru yō ni narimasendeshita.
I studied English for one year, but I could not become a fluent speaker.
To sum up
In this post, we’ve covered the differences between how なる[naru] and する[suru] are used to describe changes in state or behavior. Here are some charts to summarize!
なる and する with nouns and adjectives:
Does the subject have control over the change?YESNOUse なる!
Use する!
Are you using an i-adjective?Are you using an i-adjective?YESNOYESNODrop い + く + なる
Add い + なる
Drop い + く + なる
Add い + なる
なる and する with verbs to describe changes in behavior:
Are you describing a change or a decision to change?CHANGEDECISIONUse よう!
Use こと!
Does the subject have control?Does the subject have control?YESNOYESNOIntentional change
よう + こ + するNatural change
よう + こ + なるDecision to change
こと + に + するA mandated change
こと + に + なる
Ready to practice? Check out this sheet of exercises to help you practice using なる and する to describe changes of state! Happy learning!
