If you have ever stared at a JLPT question with four options like ようにした, ことにした, ようになった, and ことになった, you are in good company. These four patterns look nearly identical, yet each says something different. The difference comes down to two questions: who decides, and is it a change over time?
The 2×2 grid
| Pattern | Core meaning | Who or what drives it |
|---|---|---|
| ことにする | decide to | the speaker's own decision |
| ようにする | make an effort to / make sure that | the speaker's ongoing effort |
| ようになる | come to be able to / come to do | gradual change |
| ことになる | it has been decided that | other people, rules, or circumstances |
Think of する as "I do it" and なる as "it becomes." Then ask whether the pattern is about a decision or arrangement (こと) or about a habit, ability, or effort (よう).
ことにする: I decided to
This pattern expresses your own decision.
- 来月から毎朝走ることにしました。— I've decided to run every morning starting next month.
- ダイエットのため、甘いものを食べないことにした。— For my diet, I decided not to eat sweets.
Form: plain dictionary or ない form + ことにする. The decision is made by the speaker.
ようにする: I try to / I make sure to
This pattern expresses effort or care, an ongoing attempt to do something, or to ensure it happens.
- 毎日日本語を聞くようにしています。— I try to listen to Japanese every day.
- 遅れないようにしてください。— Please make sure you aren't late.
It is softer than ことにする. You are not stating a one-time decision; you are describing a conscious habit or request. Compare:
- 野菜を食べることにした — I decided to eat vegetables (a decision).
- 野菜を食べるようにしている — I try to eat vegetables (an ongoing effort).
ようになる: change to being able to / starting to
This pattern expresses a change in ability or habit over time.
- 日本語が話せるようになりました。— I've become able to speak Japanese.
- 最近、早く起きるようになった。— Recently I've started getting up early.
It describes a result of gradual change. The speaker does not necessarily decide; things have simply changed. The negative form ～なくなる means "no longer": 食べられなくなった (can no longer eat).
ことになる: it has been decided / it works out that
This pattern expresses a decision or arrangement made by someone other than (or beyond) the speaker, or a result that comes about.
- 来月、大阪に転勤することになりました。— It's been decided that I'll be transferred to Osaka next month.
- この部屋は会議で使わないことになっている。— It's the rule that this room isn't used for meetings.
It sounds natural when the decision is made by the company, family, circumstances, or rules. Also common in announcements, where it softens the speaker's role: 結婚することになりました (we're getting married, a polite phrasing).
A quick decision flow
- Did I decide this myself? → ことにする
- Am I describing a continuing effort or request? → ようにする
- Has an ability or habit changed over time? → ようになる
- Was it decided by others/circumstances, or is it a rule? → ことになる
The "ている" variations
Both ことにしている and ようにしている mean "make it a rule to / try to." Compare:
- 毎晩十時に寝ることにしている。— I've made it a rule to go to bed at ten every night. (a firm personal rule)
- 毎晩早く寝るようにしている。— I try to go to bed early every night. (a softer effort)
For how ている works in general, see ている has five meanings.
Common errors
- Using ようになる for a decision. ✕ 来月から走るようになりました when you mean I decided to; use ことにしました.
- Using ことになる when you decided yourself. It sounds like someone else decided. (Though Japanese speakers sometimes use it deliberately to soften.)
- Forgetting the ない form. The negative decision is ～ないことにする; the negative effort is ～ないようにする.
Tips for the JLPT
Read the sentence for hints:
- Time words like だんだん, 最近, 以前は〜が、今は suggest ようになる.
- Words like 会社の都合で, 決まりで, 規則で suggest ことになる.
- First-person decisions with 決めた, 今日から suggest ことにする.
- 気をつける, 努力する, できるだけ suggest ようにする.
When you miss one of these in practice, add it to your mistake log with the clue word you overlooked. That is what turns a confusing grammar pair into an automatic choice.
Where to go from here
These patterns belong to the N4–N3 range described in the JLPT N4 study plan, and the JLPT preparation guide shows the whole path. JLPT Ready's Learn section gives each grammar point a plain-language explanation and links it to the practice questions that test it, with an AI explanation for every question. You can start free with N5, no card required.