〜ことだ: Strong Advice ('You Should')
What it means
〜ことだ is used to strongly recommend a course of action to someone — to tell them, in effect, "the smartest thing you can do here is X." It often comes from a person in a position to advise: a teacher, a senior, a parent, an expert. The tone is firm but well-meaning.
The pattern works best when there's a clear goal: 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.'
How to form it
Attach ことだ directly to a plain-form verb. Only the dictionary form (affirmative advice) and the ない form (advice against) are used here:
| 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 |
Note: 〜ことだ takes verbs only in this advice sense. You don't attach it to plain nouns or adjectives to give advice.
More examples
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.'
ことだ vs べき — practical advice vs general obligation
Both translate as "should," but they sit at different levels:
- 〜ことだ = practical advice for this situation. It's personal — "here's what I'd tell you to do." Best with a goal in mind: 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, what one ought to do as a rule: 約束は守るべきだ ("you should keep your promises"). See 〜べき.
So 困っている人は助けるべきだ ("one should help people in need" — a principle) uses べき, while 困ったときは先生に相談することだ ("when you're in trouble, you should consult your teacher" — concrete advice) uses ことだ.
ことだ vs the nominalizer こと
Don't confuse advice-giving 〜ことだ with the plain nominalizer こと, which just turns a verb into a noun ("the act of doing"):
- 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 noun)
The advice meaning depends on context and the firm, directive tone — and it almost always appears as だ (plain) rather than the softer です.
A quick note: the exclamatory 〜ことか
You may also meet 〜ことか, which looks similar but is unrelated. It's an exclamation of strong emotion — "how very…!": どんなに心配したことか ("how worried I was!"). That ことか expresses feeling, not advice, so keep it separate from 〜ことだ.
Common mistakes
- Using ことだ for general truths. ことだ is advice to a person, not a statement about how things are. "Children should sleep a lot" as a general truth is 子どもはよく寝るものだ (〜ものだ), not ことだ.
- Adding it to nouns or adjectives. 〜ことだ for advice attaches to verbs: 早く寝ることだ (✓). For "you should be careful," use the verb: 気をつけることだ (✓).
- Using です to soften it. Advice 〜ことだ stays plain: 練習することだ. Tacking on です (練習することです) shifts it toward the nominalizer reading.
- Reaching for ことだ when you mean a principle. Moral "should" is べき: 嘘をつくべきではない ("you shouldn't lie" — a rule), not 嘘をつかないことだ unless you mean concrete advice in the moment.
Quick recap
- 〜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).
- 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.
Your turn
Choose the sentence that uses 〜ことだ for advice correctly.
Start the 5-question drill →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.