事だ
Should, Ought
Structure
Verb［ない］ + こと + だ
Explanation
When used at the end of a sentence, the particle こと serves two main purposes. They are:
願望や軽い命令を表す - To express a wish or a gentle command.
感嘆や疑問を表す - To convey surprise or uncertainty.
This grammar lesson will concentrate on the first usage, since the 'surprise' meaning is less frequent in contemporary Japanese and is typically used by female speakers.
To indicate that an action is expected or required, こと is attached to the plain form (dictionary or ない form) of a verb. It is commonly followed by the auxiliary verb だ, though this is not a strict rule. This pattern generally translates to 'one should/should not (do A)' or 'you ought to/ought not (to do A)'.
- 嫌なときでも、毎日ちゃんと復習することだ。Even when you don't feel like it, you should review your studies properly every day.
- 図書館は夜９時に閉まります。必ずその前に出ることだ。みんな、聞いているか。The library closes at 9 p.m. You are to leave before then without fail. Is everyone listening?
- どんな理由があっても約束を破らないことだ。You shouldn't break a promise, whatever the reason may be.
- 問題が起きたら、一人で悩まないことだ。すぐに上司に相談するように。If a problem occurs, you should not try to handle it alone. Make sure you consult with your boss right away.
Caution
This usage of こと carries a nuance of authority, making it common for stating established rules or expectations (often seen on public signs in stores, parks, etc.). For this reason, it is unsuitable for offering general advice, particularly to individuals of a higher social standing.
- 先生、授業はもっと面白くすることだ。Teacher, you should make your classes more interesting.
Examples
疲れているなら、無理をしないでしっかり休む事だ。
If you're tired, you should rest well and not push yourself too hard.
一度約束したからには、必ず守る事だ。
Once you make a promise, you must keep it.
仕事でミスをしたら、すぐに報告する事だ。
If you make a mistake at work, you should report it immediately.
日本語がうまくなりたいなら、毎日練習する事だ。
If you want to get good at Japanese, you ought to practice every day.
いつも文句ばかり言っていないで、まずは感謝する事だ。
Instead of always complaining, you should first try to be grateful.
健康でいたいなら、野菜をたくさん食べる事だ。
If you want to be healthy, you should eat a lot of vegetables.
意見が違っても、相手の話を最後まで聞く事だ。
Even if your opinions differ, you ought to listen to what the other person has to say.
新しい言語を学ぶ上で最も重要なのは、間違いを恐れない事だ。
The most important thing when learning a new language is that you shouldn't be afraid of making mistakes.
一度や二度の失敗でくよくよしない事だ。
You shouldn't mope about one or two failures.
夜遅く一人で歩く時は、周りに注意する事だ。
When walking alone late at night, you should pay attention to your surroundings.
最近、太ってきたな。もっと運動する事だ。
I've been gaining weight recently. I really ought to exercise more.
風邪をひいているんだから、今日は暖かくして寝る事だ。
Since you have a cold, you should stay warm and get some sleep today.