〜ことにする means “decide to”; 〜ことになる means “it has been decided” or “it comes about.” Use ことにする when foregrounding a person’s decision and ことになる when presenting the resulting arrangement without naming the decider. ことにしている often describes a self-set practice; ことになっている can describe an established rule or schedule.
also written koto ni shimashita / koto ni narimashita
I decided to · it was decided that
Sentences
6 sentences, word by word
polite past · your own call
polite
、。
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来月
らいげつ ［1］
next month
noun · a time word, so it needs no particle
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会社
かいしゃ ［0］
company; the firm
noun · 会 meet + 社 company
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を
を
marks the direct object
particle · pronounced お
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辞める
やめる ［0］
to quit; to resign from
ichidan verb · 辞めます／辞めた
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こと
こと
the act of; the fact of
noun · turns the verb in front into a noun
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に
に
onto — settling on
particle · marks the point a choice lands on
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しました
しました
decided; made it so
polite past of する · the decision lives in this verb
〜ことにするN4decide to
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I've decided to leave the company next month.
polite past · it came about
polite
、。
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来月
らいげつ ［1］
next month
noun · a time word, so it needs no particle
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会社
かいしゃ ［0］
company; the firm
noun · the same word as the sentence above
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を
を
marks the direct object
particle · pronounced お
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辞める
やめる ［0］
to quit; to resign from
ichidan verb · unchanged — only the ending moved
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こと
こと
the act of; the fact of
noun · turns the verb in front into a noun
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に
に
onto — settling on
particle · the same に as in the sentence above
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なりました
なりました
it came to be
polite past of なる · nobody is named as the decider
〜ことになるN4it was decided that
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It's been decided that I'll be leaving the company next month.
plain past of なる · the schedule settled, and no one is credited
〜ことになるN4it was decided that
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The meeting ended up being set for Friday.
a decision you keep renewing
plain
、。
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毎日
まいにち ［1］
every day
noun · used adverbially, no particle needed
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日記
にっき ［0］
diary; journal
noun · 日記をつける is the set phrase
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を
を
marks the direct object
particle · pronounced お
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書く
かく ［1］
to write
godan verb · 書きます／書いた
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こと
こと
the act of; the fact of
noun · turns the verb in front into a noun
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に
に
onto — settling on
particle · marks the point a choice lands on
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している
している
am keeping to it
て-form of する ＋ いる · the decision is still running
〜ことにしているN4make a point of
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I make a point of writing in my diary every day.
the rule as it stands
plain
。
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社内
しゃない ［1］
inside the company
noun · 社 company + 内 inside
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で
で
in; at — where it happens
particle · where the action happens, or the manner it happens in
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は
は
as for — and by contrast
particle · pins 社内 as the setting, hinting that elsewhere differs
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英語
えいご ［0］
English (the language)
noun · 英 England + 語 language
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を
を
marks the direct object
particle · pronounced お
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話す
はなす ［2］
to speak; to talk
godan verb · 話します／話した
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こと
こと
the act of; the fact of
noun · turns the verb in front into a noun
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に
に
onto — settling on
particle · marks the point a rule lands on
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なっている
なっている
it stands decided
て-form of なる ＋ いる · a rule in force, not a one-time event
〜ことになっているN4be supposed to
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Inside the company we're supposed to speak English.
Structure
How do you form 〜ことにする and 〜ことになる?
Verb［dictionary・ない］＋ことにする
辞める → 辞めることにした. The decision is yours, and する is the verb that carries it.
Verb［dictionary・ない］＋ことになる
辞める → 辞めることになった. Same slot in front; only the last verb changed, and with it who decided.
Verb［dictionary・ない］＋ことにしている
書くことにしている — a decision you renew every day. “I make a point of it.”
Verb［dictionary・ない］＋ことになっている
話すことになっている — the rule as it currently stands. Schedules, company policy, house rules.
Meaning
What's the difference between 〜ことにする and 〜ことになる?
Both start the same way. こと turns the verb in front of it into a noun — 辞める “to quit” becomes 辞めること “quitting” — and then something happens to that noun. The whole contrast sits in which verb does the happening.
する is you acting on it.辞めることにしました is the sound of a decision being made, and you made it. Nobody else is in the sentence. It is the natural answer to “what did you decide?”
なる is it becoming so.辞めることになりました puts the outcome in front and leaves the decider out. The change might have been arranged by someone else, or the speaker may simply present it as settled. Even a decision you helped make may be phrased with なる when the focus is on the outcome.
Add 〜ている to either and the one-off becomes ongoing. ことにしている is a rule you gave yourself and keep. ことになっている is a rule that simply stands — the meeting is at three, shoes come off at the door — with nobody claiming authorship.
Watch out
Where does this go wrong?
Reading ことになりました as “I had no choice”
Japanese speakers announce their own wedding, their own new job, their own move with なる. It isn't a dodge — it frames the news as something that came about, which is politer than claiming the decision. Take it as coercion and you'll misread half the announcements you see.
Putting a verb you don't control in front of する
雨が降ることにする is not a sentence. The verb before ことにする has to be something a person can decide to do. Weather, ageing, and other people's behaviour all take ことになる instead.
Negating the wrong half
The negative goes on the verb in front: 行かないことにした, “I decided not to go.” 行くことにしなかった means something else entirely — that you never made the decision at all.
Also asked
Questions people ask about ことにする and ことになる
Is ことになりました always about someone else deciding?
No. It's the standard way to announce your own news — a wedding, a transfer, a resignation — because なる puts the event in front and you behind it. Japanese hears that as modest, not passive.
What's the difference between ことにする and つもりだ?
つもり is an intention you're holding; ことにする is the moment it becomes a decision. 行くつもりです is “I plan to go”; 行くことにしました is “it's settled.”
Can I use ことにする with a noun?
Not directly — こと needs a verb in front of it. For a noun, drop こと and use にする on its own: コーヒーにします, “I'll have the coffee.”
Why is it に and not を?
This is the “settle on” する, the same one in コーヒーにする. に marks the point a choice lands on. を would make it a plain “do”, which isn't the meaning.
What does ことになっている mean on a schedule?
The arrangement as it currently stands. 会議は三時からということになっています — the meeting is set for three. Nobody claims authorship; it's simply how things are.
Is ことにしている the same as ようにしている?
Close, not equal. ことにしている is a rule you set and keep. ようにしている is an effort, with room to fail: 野菜を食べるようにしている, “I try to eat vegetables.”
References
Sources and usage notes
Japan Foundation: こと (1) — Explains ことにする as a decision, ことにしている as a habit, ことになる as a result or decision, and ことになっている as a rule.
