〜ことだろう
Formation
Meaning
An expression used to express strong emotion or deep feeling. It often occurs with adverbs like 'どんなに' (how much), 'なんと' (what a...), or 'どれほど' (how much).
Note
Indicates a deep emotional realization, emphasis, or a strong exclamation. It is used to express that the speaker is deeply moved or impressed by the extent of something. It often pairs with interrogative adverbs like 'どんなに' (how much), 'どれほど' (to what extent), or 'なんと' (how/what a...). '〜ことか' is specifically literary/written and very emphatic, while '〜ことだろう' and '〜ことでしょう' are more common in formal speech or reflective writing. It expresses the speaker's subjective feeling rather than an objective record.
Examples
合格を知ったら、両親はどんなに喜ぶことだろう。
How happy my parents will be when they find out I passed!
初めて日本へ行った時は、どれほど驚いたことか。
How surprised I was when I went to Japan for the first time!
合格したと聞いて、本人はどんなにか嬉しいことだろう。
How happy he must be to hear that he passed!
異国の地で一人で生活するのは、なんと寂しいことか。
How lonely it must be to live alone in a foreign land!
このプロジェクトを完成させるのは、どれほど大変なことでしょう。
How difficult it must be to complete this project!
子供たちの成長を見るのは、なんと幸せなことだろう。
How happy it is to see the children's growth!