Examples
Meaning
〜ようになる describes a change in ability, habit, or state. 〜ことになる describes a decision, arrangement, or outcome that has been set.
Formation
〜ようになる usually follows a verb in dictionary, potential, or negative form. 〜ことになる follows a verb in dictionary or negative form.
Usage
Use 〜ようになる for gradual changes such as becoming able to read kanji or starting to exercise every morning. Use 〜ことになる for decisions or arrangements such as being assigned to work in Osaka.
Nuance
〜ようになる focuses on personal or situational change over time. 〜ことになる focuses on the fact that a decision or arrangement has been made, often by outside circumstances.
Comparison
毎朝早く起きるようになりました means I started waking up early every morning. 来月から早番で働くことになりました means it has been decided that I will work the early shift from next month.
Common Mistakes
A common mistake is using 〜ようになる for an official assignment or schedule. If the key point is that it has been decided, 〜ことになる is better.
Related Grammar
〜ようになる
〜ようになる expresses a change into a new state, habit, or ability, especially something that has become possible over time.
〜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.
〜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.
〜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.