Introduction
In Japanese, ことにする (koto ni suru) is a useful phrase that means “decide to do something.” It helps you express decisions you have made. This grammar follows the short form present tense of a verb and can also be used with a negated verb to say you have decided not to do something.
Let’s break it down and learn how to use ことにする (koto ni suru) properly!
What It Means
The phrase ことにする (koto ni suru) means “decide to do…” It is used to talk about decisions you have made for yourself or a group.
- verb (short, present) + ことにする (koto ni suru) → decide to do something
- verb (short, present, negative) + ことにする (koto ni suru) → decide not to do something
When to Use It
Use ことにする (koto ni suru) when:
- You make a decision about something.
- You decide on a new habit or rule for yourself.
- You suggest an action after thinking about it carefully.
If you are making a personal decision, use ことにしました (koto ni shimashita) for past decisions or ことにします (koto ni shimasu) for present/future decisions.
Examples
1. Talking About a Decision
車を買うことにしました。
(Kuruma o kau koto ni shimashita.)
→ We have decided to buy a car.
毎朝ジョギングすることにします。
(Maiasa joggingu suru koto ni shimasu.)
→ I will start jogging every morning.
2. Deciding NOT to Do Something
夜遅くまでゲームをしないことにしました。
(Yoru osoku made geemu o shinai koto ni shimashita.)
→ I have decided not to play games late at night.
甘いものを食べないことにします。
(Amai mono o tabenai koto ni shimasu.)
→ I will not eat sweets. (Decision for the future)
3. Making a Careful Suggestion
We sometimes use the volitional form with ことにする, like ことにしよう (koto ni shiyou) instead of the simple volitional form (like 行こう (ikou)).
今年の夏はベトナムに行くことにしよう。
(Kotoshi no natsu wa Betonamu ni iku koto ni shiyou.)
→ Let’s take the plunge. Let’s go to Vietnam this summer.
この仕事を引き受けることにしよう。
(Kono shigoto o hikiukeru koto ni shiyou.)
→ Let’s decide to take this job.
This ことにしよう (koto ni shiyou) form shows that the decision was made after thinking about it.
Notes
- ことにする (koto ni suru) is for active decisions you make yourself. If something naturally happens, use ことになる (koto ni naru) instead.
- 来月、日本へ行くことになりました。 (Raigetsu, Nihon e iku koto ni narimashita.)
→ It has been decided that I will go to Japan next month. (Not my decision)
- 来月、日本へ行くことになりました。 (Raigetsu, Nihon e iku koto ni narimashita.)
- ことにしている (koto ni shiteiru) means a regular habit, rule or practice you have set for yourself.
- 毎晩10時に寝ることにしています。 (Maiban juuji ni neru koto ni shiteimasu.)
→ I have decided to sleep at 10 PM every night. (Ongoing habit)
- 毎晩10時に寝ることにしています。 (Maiban juuji ni neru koto ni shiteimasu.)
Conclusion
ことにする (koto ni suru) is a great way to express decisions in Japanese! Use it to talk about choices you make for yourself and when suggesting something after thinking about it.
Try using ことにする (koto ni suru) in your daily conversations and writing!
Recommended Resources
To deepen your understanding of ことにする (koto ni suru) in Japanese, I recommend the book Making Sense of Japanese: What the Textbooks Don’t Tell You by Jay Rubin. This resource explains complex Japanese grammar points, including decision-making expressions like ことにする, in a clear and engaging way. It’s well-regarded for helping learners grasp the nuances of Japanese that textbooks often overlook.
