8.16 ～ことにする・～ことになる — Decide / It Has Been Decided

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Overview

Learn the important distinction between ～ことにする (personal decision) and ～ことになる (external outcome or circumstance). This pair is essential for natural Japanese at N4 level and above.

～ことにする — personal decision

Plain form + ことにする

This expresses a deliberate personal decision — you chose to do something.

。

I decided to study Japanese every day.

。

I decided to quit smoking.

。

Let's decide to eat here.

～ことになる — external outcome

Plain form + ことになる

This expresses that something has been decided or arranged — not by your own choice, but by circumstances, rules, or others. It takes the agency away from the speaker.

、。

It has been decided that I'll be transferred to Tokyo next month.

。

There is supposed to be a meeting tomorrow (that's how things stand).

。

It has been decided that it's prohibited by the rules.

Contrast

Pattern	Who decides?	Feeling
～ことにする	The speaker (I did)	Personal, active
～ことになる	Circumstances/others	Passive, external

This distinction matters in Japanese culture. Saying ことになる is often more polite because it avoids attributing the decision directly to yourself or any individual.

。

I decided to go to Japan. (my choice)

。

It's been decided / it turned out I'll go to Japan. (how things ended up)

Dialogue

あAきごう：けっこん結婚することにしました。 bBきごう：おめでとうございますきごう！

あAきごう：らいげつ来月からおおさか大阪にてんきん転勤することになりました。 bBきごう：そうですか。たいへん大変でしたね。

あAきごう：あたらしい新しいきそく規則で、ざんぎょう残業きんし禁止になることになっています。 bBきごう：ほんとう本当ですか。いいですね。

A: I decided to get married. B: Congratulations!

A: It has been decided that I'll be transferred to Osaka from next month. B: Is that so. That must be tough.

A: Under the new rules, overtime is being banned. B: Really. That's good.

New words

8.15 Causative

9.1 ～ば conditional

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