〜ことにする

Meaning

〜ことにする means that you decide to do something or decide not to do something. It emphasizes the act of making a decision.

Formation

Use the dictionary form before ことにする for a positive decision. Use the ない form before ことにする for a decision not to do something.

Usage

Use this pattern when you choose a course of action, make a personal rule, or announce a decision. The past form 〜ことにした is common after the decision has already been made.

Nuance

This pattern is more decision-focused than 〜つもりだ. It can sound like the speaker has chosen one option from several possibilities.

Comparison

〜ようと思う expresses what you are thinking of doing. 〜つもりだ shows intention. 〜ことにする highlights the decision itself.

Common Mistakes

A common mistake is using the ます form before ことにする. Say 勉強することにしました, not 勉強しますことにしました. Also, do not confuse it with 〜ことになる, which often describes a decision made by circumstances or other people.