Examples
Meaning
〜ことにする means to decide to do something or decide not to do something. It presents the action as a decision made by the speaker or the subject.
Formation
Use the dictionary form or negative form of a verb before ことにする. ことにしました is common when announcing a decision that has already been made. ことにしています can describe a personal rule or habit.
Usage
Use this pattern when talking about personal decisions, plans, lifestyle choices, or rules you set for yourself. It is common in daily conversation and polite explanations.
Nuance
This pattern emphasizes agency. The speaker or subject chose the action. It is stronger as a decision than 〜ようにする, which often emphasizes effort or habit.
Comparison
Compared with 〜ことになる, 〜ことにする is a personal or subject-driven decision. Compared with 〜予定だ, it focuses on deciding, not simply having a schedule.
Common Mistakes
A common mistake is using 〜ことにする when the decision was made by a company, school, or outside circumstances. In that case, 〜ことになる is often more natural.
Related Grammar
〜ことになる
〜ことになる means that something has been decided or arranged, often by circumstances, a group, or someone other than the speaker alone.
〜ことになっている
〜ことになっている describes a rule, arrangement, schedule, or established decision that is already in place.
〜ことにする・〜ことになるの違い
This page explains the difference between 〜ことにする and 〜ことになる: deciding by oneself versus having something decided or arranged.
〜ようにする
〜ようにする expresses making an effort, setting a habit, or trying to make sure something happens or does not happen.