Four patterns trip up every intermediate learner because English hides their differences inside three sloppy verbs — decide, become, get to. But ことにする, ことになる, ようにする, and ようになる are not four things to memorize. They are a clean 2×2 grid built from just two questions. Answer both and the right form is forced. This page lays the grid bare so the whole family clicks into place at once.
The two axes
Axis 1 — Who drives it? する vs なる. This is the contrast English has no single word for. する ("do / make") means the subject acts on the world — you reached out and made it so. なる ("become") means the world changes on its own — it came about, developed, was arranged. This one morpheme swap carries the entire difference between agency and spontaneity.
Axis 2 — What kind of thing? こと vs よう. こと (the nominalizer) frames a discrete decision or event — a single point where a course of action is fixed. よう frames a target state or gradual change — a way you want things to be, or a new ability/habit developing over time.
Cross the two axes and you get exactly four cells:
| する — I act on the world | なる — the world changes on its own | |
|---|---|---|
| こと — a discrete decision / event | ことにする I decide to 走ることにした "I decided to run" | ことになる it's decided / comes about 転勤することになった "it's been decided I'll transfer" |
| よう — a target state / gradual change | ようにする I make an effort toward 走るようにしている "I make a point of running" | ようになる a state develops 走れるようになった "I became able to run" |
Each cell links to its full page: ことにする, ことになる, ようにする, ようになる. Here we focus on telling them apart.
The four corners in the wild
健康診断で医者に言われて、毎朝走ることにした。
kenkō shindan de isha ni iwarete, maiasa hashiru koto ni shita
After what the doctor said at my checkup, I decided to run every morning. (my own decision → する)
リレーで私がアンカーを走ることになった。
rirē de watashi ga ankā o hashiru koto ni natta
It's been decided that I'll run the anchor leg in the relay. (assigned by others → なる)
最近は運動不足なので、一駅分歩くようにしている。
saikin wa undō busoku na node, hito-eki-bun aruku yō ni shite iru
I've been short on exercise lately, so I make a point of walking one station's worth. (ongoing effort → する)
膝を痛めていたが、また走れるようになった。
hiza o itamete ita ga, mata hashireru yō ni natta
I'd hurt my knee, but I've become able to run again. (ability developed → なる)
Notice the pairs. 走ることにした and 走ることになった describe the same act of running — they differ only on who chose it. 走るようにしている and 走れるようになった both concern building running into your life over time — they differ only on whether you're pushing (する) or it developed (なる).
Read the two questions and the form is forced
1. Who drives it? I chose/act → する. It happened / was arranged → なる.
2. What kind? A one-time decision or event → こと. A gradual state / ability / habit → よう.
Two answers, one cell. No memorization of four separate rules.
Walk it through:
- "I decided to quit smoking." → I chose it (する) + a discrete decision (こと) → やめることにした.
- "It's been decided the meeting is Monday." → arranged by others (なる) + a fixed event (こと) → 月曜日に行うことになった.
- "I try not to eat late at night." → my ongoing effort (する) + steering a habit (よう) → 食べないようにしている.
- "I've come to read kanji." → developed in me (なる) + a new ability (よう) → 読めるようになった.
One verb through all four cells
To feel the axes with nothing else changing, hold the verb 走る ("to run") constant and slide only the grammar:
| Form | Japanese | Meaning |
|---|---|---|
| ことにする | 走ることにした | I decided to run (my call) |
| ことになる | 走ることになった | it's been decided I'll run (arranged) |
| ようにする | 走るようにしている | I make a point of running (effort) |
| ようになる | 走れるようになった | I became able to run (change) |
One tiny detail worth flagging: in the ようになる cell the verb quietly shifts to its potential form (走る → 走れる), because "come to be able to run" is an ability change. That is the norm for ようになる and part of why it's the go-to for describing new skills.
The social twist: なる for modesty
Here is where the grid stops being merely logical and becomes cultural. Japanese speakers frequently pick the なる side even for things they chose themselves, because backgrounding your own agency sounds humble. Announcing a decision with the する-frame can read as self-important; framing it as an outcome spreads the credit onto circumstances.
実は、来月で会社を辞めることになりまして。
jitsu wa, raigetsu de kaisha o yameru koto ni narimashite
Actually, it's come about that I'll be leaving the company next month. (formal — softened even though quitting was my choice)
この春から、日本で働くことになりました。
kono haru kara, nihon de hataraku koto ni narimashita
From this spring, it's been arranged that I'll be working in Japan. (a modest announcement of your own move)
Both speakers made their own choices, yet both use なる. English has no grammatical equivalent — you'd need to add words ("as it happens…," "we're pleased to share…"). Japanese does it with a single morpheme. So when you choose between する and なる, you are choosing not just facts but stance: how much personal will you want to show.
Common mistakes
❌ 転勤することにしました。
Claims you personally chose a transfer your company arranged — and sounds immodest.
✅ 転勤することになりました。
tenkin suru koto ni narimashita
It's been decided that I'll transfer. (arranged — and humbler)
When circumstances or others decide — or when you simply want to be modest — cross to the なる column.
❌ 日本語が話せることになった。
Uses こと (a decision) for what is really a gradual ability change.
✅ 日本語が話せるようになった。
nihongo ga hanaseru yō ni natta
I became able to speak Japanese.
An ability or habit that grew over time is よう, not こと. こと is for decisions and fixed events, not for skills ripening in you.
❌ 毎日運動することにしている。
If you mean 'I try to exercise daily,' this overstates it as a fixed rule rather than an effort.
✅ 毎日運動するようにしている。
mainichi undō suru yō ni shite iru
I make a point of exercising every day. (an effort, lapses allowed)
For trying to keep a habit, use よう (effort toward a state). こと would frame it as an inflexible personal rule you've decided on.
❌ 甘いものを食べないようになった。
Clumsy negative — Japanese uses 〜なくなる for 'came to no longer.'
✅ 甘いものを食べなくなった。
amai mono o tabenaku natta
I came to no longer eat sweets.
The negative counterpart of ようになる is 〜なくなる, not ×〜ないようになる — a trap covered in full on the ようになる page.
Summary
| Form | Axis 1 (drive) | Axis 2 (kind) | English |
|---|---|---|---|
| ことにする | する — I act | こと — decision | I decide to |
| ことになる | なる — it happens | こと — decision/event | it's decided / comes about that |
| ようにする | する — I act | よう — state/change | I make an effort to |
| ようになる | なる — it happens | よう — state/change | I come to be able to / start to |
- Two axes decide everything: する (I act) / なる (it happens) × こと (a decision) / よう (a gradual change).
- Ask who drives it and what kind of thing it is; the two answers force the exact form.
- Japanese leans to the なる side for modesty, so even your own choices may surface as ことになる / ようになる.
- The negative of ようになる is the separate 〜なくなる — don't build it by negating the verb inside.
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Start learning Japanese→Related Topics
- 〜ことにする: Deciding ToN3 — How Japanese expresses a personal decision — literally 'making it into the fact that…' with こと + する — and why that する marks the choice as your own act of will.
- 〜ことになる: It Comes About ThatN3 — How Japanese frames a decision as an outcome that arrives — 転勤することになった — backgrounding who decided, and why speakers reach for this humble なる-frame even for their own choices.
- 〜ようにする: Making an Effort ToN3 — How Japanese expresses steering your own behavior toward a goal — 毎日運動するようにする, 忘れないようにする — and why this ongoing effort is a different act from a one-time decision.
- 〜ようになる: Coming To Be Able / DoN3 — How Japanese marks a gradual change into a new ability or habit — 話せるようになった, 'became able to speak' — why it loves the potential form, and why its negative is 〜なくなる.