こと (written as こと or 事) turns verbs into noun clauses. Four patterns look almost identical ことがある, ことにする, ことになる, ことができる, but they have completely different meanings. Mixing them up changes what you're saying dramatically.
| Pattern | Meaning | Who decides? | Verb form |
|---|---|---|---|
| 〜ことがある | sometimes / have experienced | n/a | Dictionary (sometimes) / た-form (experience) |
| 〜ことにする | decide to / have decided to | speaker decides | Dictionary form |
| 〜ことになる | it has been decided that / it will turn out that | externalnatural | Dictionary form |
| 〜ことができる | can / be able to | n/a | Dictionary form |
1. 〜ことがある "sometimes" or "have done before"
This pattern has two distinct uses depending on verb tense. With dictionary form, it means something happens occasionally ("there are times when"). With た-form, it means you have the experience of having done something at some point.
Dictionary form → "sometimes"
た-form → "have the experience of"
2. 〜ことにする "I've decided to" (speaker's choice)
The speaker actively makes a decision. The choice is yours. ことにした = decided (past). ことにします = deciding now or going to decide. Very common for announcing personal plans or changes in behavior.
3. 〜ことになる "it's been decided" (external/natural outcome)
The decision or outcome comes from outside the speaker a company, fate, circumstances. The speaker didn't choose it; it just came to be that way. Very common in Japanese workplaces and formal announcements, because it lets you report news without claiming personal responsibility.
4. 〜ことができる "can / be able to"
Expresses ability or possibility. Interchangeable with the potential verb form (e.g. 食べられる), but ことができる is more formal and explicit common in written language, resumes, and careful speech.
ことにする vs ことになる the key distinction
This is the most commonly confused pair. The difference: にする = you chose it. になる = it happened externally.
ことにしました (I decided)
日本に行くことにしました。
I decided to go to Japan. (my own choice)
ことになりました (it was decided)
日本に行くことになりました。
It was decided that I'd go to Japan. (company sent me / circumstances led to it)
Japanese people often prefer ことになりました even for their own decisions in professional settings it sounds more humble, as if the situation decided rather than your own ego.
Pick the right こと pattern
Which pattern fits the situation?
You personally decided to start running every morning it's your own lifestyle choice, nobody told you to.
Your company announced you will be transferred to Osaka next month. You had no say in the matter.
You want to say you can speak Japanese.
You've climbed Mt. Fuji once before. You want to express that past experience.
Work sometimes runs late. It's not every day just occasionally.
Quick map: ことがある (experience or habit) → ことができる (ability) → ことにする (I decided) → ことになる (externally decided). The にする/になる distinction is the one to really internalize.