〜ことだ: Strong Advice ('You Should')
The advice it delivers
〜ことだ strongly recommends a course of action to someone — it tells them, in effect, "the smartest thing you can do here is X." It usually comes from a person in a position to advise: a teacher, a senior, a parent, an expert, and the tone is firm but well-meaning. The pattern lands hardest when there's a clear goal behind it: if you want this result, then do this.
上手になりたいなら、毎日練習することだ。
じょうずに なりたいなら、まいにち れんしゅう する ことだ。
If you want to get good, you should practice every day.
Classic structure: goal (〜たいなら) + advice (〜ことだ).
体のために、無理をしないことだ。
からだの ために、むりを しない ことだ。
For your health, you shouldn't overdo it.
ない-verb + ことだ = advice not to do something.
先生は「とにかく早く寝ることだ」と言った。
せんせいは「とにかく はやく ねる ことだ」と いった。
The teacher said, 'Above all, you should go to bed early.'
Building it: verb + ことだ
Attach ことだ directly to a plain-form verb. Only two shapes appear here — the dictionary form for affirmative advice, and the ない form for advice against:
| Base | Form | Result | Meaning |
|---|---|---|---|
| 練習する | dictionary + ことだ | 練習することだ | (you) should practice |
| 休む | dictionary + ことだ | 休むことだ | (you) should rest |
| 無理をする | ない + ことだ | 無理をしないことだ | (you) shouldn't overdo it |
| 諦める | ない + ことだ | 諦めないことだ | (you) shouldn't give up |
The verb restriction is strict: advice ことだ takes verbs only. You don't hang it off a plain noun or adjective — for "you should be careful," reach for the verb 気をつけることだ, not a noun.
Where you'll hear it
緊張しているなら、深呼吸することだ。
きんちょう して いるなら、しんこきゅう する ことだ。
If you're nervous, you should take a deep breath.
モチ、合格したいなら、まず計画を立てることだ。
モチ、ごうかく したいなら、まず けいかくを たてる ことだ。
Mochi, if you want to pass, the first thing to do is make a plan.
風邪のときは、ゆっくり休んで、薬を飲むことだ。
かぜの ときは、ゆっくり やすんで、くすりを のむ ことだ。
When you have a cold, you should rest well and take your medicine.
弟に「人の話は最後まで聞くことだ」と教えた。
おとうとに「ひとの はなしは さいごまで きく ことだ」と おしえた。
I taught my little brother, 'You should listen to people until they've finished.'
Sorting it from べき and ものだ
Three N3 patterns can all surface as English "should," but each carries a different flavour, and picking the wrong one changes the message:
- 〜ことだ = practical advice for the situation in front of you. It's personal — "here's what I'd tell you to do" — and pairs naturally with a goal: 速くなりたいなら走ることだ ("if you want to get faster, you should run").
- 〜べき = moral or general obligation — what's right as a rule. 約束は守るべきだ ("you should keep your promises") states a principle; so does 困っている人は助けるべきだ ("one should help people in need"). When you mean a standing rule rather than a here-and-now tip, use 〜べき, not ことだ.
- 〜ものだ = how things generally are. "Children should sleep a lot" as a truth about the world is 子どもはよく寝るものだ, never ことだ — because ことだ speaks to a person, not about the world.
So 困ったときは先生に相談することだ ("when you're in trouble, consult your teacher") is concrete advice and takes ことだ, while its moral-rule cousin would swing to べき.
Why it stays だ, never です
Advice ことだ almost always ends in plain だ, and that isn't just tone — polishing it to です flips the meaning. です pushes ことだ back toward the ordinary nominalizer こと, which merely turns a verb into a noun:
- 毎日練習することだ = "You should practice every day." (advice)
- 私の趣味は毎日練習することです = "My hobby is practicing every day." (こと = "the activity of," a plain noun)
The advice reading rides on the firm, directive plain form. Tack on です and the same string of characters becomes an innocent "the act of practicing," so keep it plain when you mean to advise.
The lookalike: 〜ことか
One more form looks close but does something entirely different. 〜ことか is an exclamation of strong emotion — "how very…!" — as in どんなに心配したことか ("how worried I was!"). It voices feeling, not advice, so don't let its resemblance to 〜ことだ blur the two.
The short of it
- 〜ことだ = direct, practical advice — "the best thing is to / you should."
- Form: dictionary verb + ことだ (do) or ない verb + ことだ (don't); verbs only.
- Often from someone advising you; pairs naturally with a goal (〜たいなら…ことだ).
- vs べき = moral/general obligation; vs こと = plain nominalizer; vs ものだ = general truth.
- The exclamatory 〜ことか ("how …!") is a separate point.
Put it into practice
Choose the sentence that uses 〜ことだ for advice correctly.
＿＿＿に入れるのに最もよいものを選びなさい。
上手になりたいなら、毎日練習する＿＿＿。
Frequently asked questions
What does 〜ことだ mean?
It gives strong, practical advice for a specific situation: 'the best thing is to…' or 'you should…'. For example, 上手になりたいなら毎日練習することだ ('if you want to get good, you should practice every day'). It usually comes from someone in a position to advise.
How is ことだ different from べき?
ことだ is concrete advice for the situation at hand and feels personal. べき is a moral or general obligation — what one ought to do as a rule. 約束は守るべきだ ('you should keep promises') is a principle; 困ったら相談することだ ('you should consult someone when in trouble') is practical advice.
Can I use です instead of だ with this ことだ?
For the advice meaning, keep it plain: 練習することだ. Switching to です (練習することです) pushes it toward the nominalizer こと ('the act of practicing'), changing the meaning.
What about 〜ことか — is it the same?
No. 〜ことか is an exclamation of strong feeling ('how very…!'), as in どんなにうれしかったことか ('how happy I was!'). It expresses emotion, not advice, and is a separate grammar point.
Where 〜ことだ fits
Don't confuse it with
- 〜べき · N3 — 〜べきだ means 'should' or 'ought to' — a strong, principled obligation. Learn how to form it, すべき vs するべき, the negative べきではない, and the regretful べきだった.
- 〜ものだ · N3 — 〜ものだ states general truths and common-sense advice, recalls how things used to be (〜たものだ), and voices strong feeling. Learn all four N3 uses and 〜ものではない.
Once this clicks, go on to
- 〜こと · N4 — こと turns a verb or clause into a noun: 話すことは難しい ('speaking is hard'). Learn the formation, こと vs の, and frames like 〜ことがある, 〜ことにする, and 〜ことになる.
More N3 grammar to explore
Keep going with related patterns at the same level:
- 〜まま — 〜まま means a state stays unchanged while something else happens: 電気をつけたまま寝た ('slept with the light on'). Learn た/ない/noun/adjective forms and そのまま.
- 〜ながら（も） — The concessive 〜ながら（も） means 'although / even though,' pointing out a contradiction between two facts about the same subject: 彼は忙しいながら、健康に気をつけない. Not to be confused with the 'while doing' ながら.
- 〜によると/によれば — によると and によれば both mean 'according to,' citing the source of information a sentence is based on (天気予報によると、明日は雨だそうだ). The sentence almost always ends in a hearsay form like そうだ or らしい.
- 〜たらいい — 〜たらいい attaches to the た-form of a verb to mean 'it would be good/nice if,' 'I wish,' or (as a question) 'what should I do' — もっと時間があったらいいのに ('I wish there were more time'). It softly expresses a hope or asks for advice.
- 〜てもかまわない — 〜てもかまわない attaches to the て-form to grant permission or express indifference — ここで吸ってもかまいません ('it's fine to smoke here'). Slightly more formal than 〜てもいい, and literally says 'even if..., it doesn't bother me.'
- 〜としたら — 〜としたら means 'if we suppose/assume that...' — it sets up a hypothetical premise and asks what follows from it. Common with もし and questions about what you'd do in that case.