〜ことだ
Formation
Meaning
An expression used when giving advice or warnings. It suggests that doing something is the best or most important course of action in a given situation. It is not used for superiors.
Note
Used to give advice, suggestions, or warnings. It implies 'the best thing to do is...' or 'you should...'. It is often used to express the speaker's personal judgment or a general truth. Because it can sound like unsolicited advice or a direct order, it is typically used towards people of equal or lower status, or in situations where advice is expected. For stronger, more obligatory advice, use '〜べきだ'. For social rules or prohibitions, use '〜ことだ' with a negative verb ('〜ないことだ').
Examples
ピアノが上手になりたければ、毎日練習することだ。
If you want to become good at the piano, you should practice every day.
太りたくなければ、夜中に甘いものを食べないことだ。
If you don't want to gain weight, you shouldn't eat sweets in the middle of the night.
日本をよく知るためには、実際に日本へ行ってみることだ。
In order to know Japan well, the best thing is to actually go there.
健康でいたければ、無理をしないことだ。
If you want to stay healthy, you shouldn't overdo it.
大切なのは、失敗を恐れずに挑戦し続けることです。
The important thing is to keep on challenging yourself without fearing failure.
風邪を早く治したければ、今日はゆっくり休むことだ。
If you want to get over your cold quickly, you should rest well today.