ことだ

Should, Must

Level 3Sounds Like kotoda

ことだ is used to provide focused advice, suggesting that a specific action is the best or only way to handle a situation. It translates to 'should' or 'the thing to do is...'

How It Works

1. Usage and Nuance
ことだ is used when the speaker wants to give strong advice. Unlike a simple suggestion, it implies that the action mentioned is the most important or effective method to reach a goal. It often appears after a conditional clause like なら or たら.

2. Social Constraints
Because this pattern sounds authoritative and slightly 'preachy,' it is generally not used toward superiors (bosses, teachers, or elders). Using it with someone of higher status can sound condescending or like you are 'talking down' to them.

3. Formation

  • Verb (Dictionary Form) + ことだ: 成功（せいこう）したければ、努力（どりょく）することだ。(If you want to succeed, you should work hard.)
  • Verb (Negative Form) + ことだ: 無理（むり）をしないことだ。(You should not overdo it.)

4. Distinction from other 'Shoulds'
While 〜べき focuses on moral or social obligations, ことだ focuses on practical advice for a specific result. While ほうがいい is a soft, casual suggestion, ことだ is a more authoritative, direct, and definitive command.

5. ことだ vs ものだ
It is important to distinguish this from ものだ. While ことだ is used for specific advice given to a specific person in a specific situation, ものだ is used for general social norms, common sense, or universal truths (e.g., 'Children should play outside').

6. Emotive/Exclamatory Usage
As a secondary function, ことだ can be used with adjectives (often expressing emotion or evaluation) to emphasize the speaker's strong feelings, translating to 'How...!' or 'It is such a...'. Formation includes い-adjective + ことだ, な-adjective + な + ことだ, and a few specific verbs expressing emotion or evaluation (often in the た or ない form) + ことだ. It is frequently paired with exclamatory adverbs like なんて or なんと. For example: なんて素晴らしいことだ (What a wonderful thing!), 困（こま）ったことだ (How troubling!), or うれしいことだ (What a joyful thing!). Note that if you use adverbs like どんなに or どれほど (How much...), the pattern usually shifts to 〜ことか or 〜ことだろう (e.g., どんなにうれしいことか), rather than using ことだ.

7. Important Restrictions

  • Interrogative Restriction: ことだ cannot be used in questions to ask for advice (e.g., どうすることですか is incorrect; instead, use phrases like どうすればいいですか).
  • Subject Restriction: When used for advice, this pattern is directed at the listener (second person), understood third parties, or used for general rules. It is not used for the speaker's own actions (first person) unless they are giving a pep talk to themselves.
  • Volitional Verb Restriction: When used for advice, ことだ can only be used with volitional verbs (actions the listener can actively control). It cannot be used with state verbs or non-volitional verbs. For example, 病気（びょうき）にならないことだ is incorrect; it must be framed as an action like 健康（けんこう）に気（き）をつけることだ.
  • No Past Tense: When used for advice, this pattern cannot be conjugated into the past tense (e.g., 早く寝ることだった is incorrect).
  • No Negative Copula: To give negative advice, use the negative verb form (ないことだ), not the negative copula (e.g., 無理をすることではない is incorrect; use 無理をしないことだ).

Examples (4)

  1. 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.

    Word by Word: Piano (particle) skillful want to become if, every day practice doing is.

    Here, the speaker is giving the 'obvious' best advice for someone who wants to improve their skills.

  2. 太りたくなかったら、夜遅く食べないことですよ。

    If you don't want to gain weight, you shouldn't eat late at night.

    Word by Word: To get fat not want if, night late eat not is (polite).

    The negative form (nai-form) is used here to advise against a specific action.

  3. 一度失敗しても、あまり気にしないことだ。

    Even if you fail once, you shouldn't worry about it too much.

    Word by Word: One time failure even if, very much care not doing is.

    This provides encouraging but firm advice on how to handle a setback.

  4. 健康になりたいなら、もっと野菜を食べることだ。

    If you want to be healthy, the thing to do is eat more vegetables.

    Word by Word: Health want to become if, more vegetables eat is.

    This shows the common structure of 'If [Goal], then [Advice] ことだ'.

Common Mistakes

  • Using it with superiors (bosses or teachers).

    先生、もっと日本語を教えることですよ。
    先生、もっと日本語を教えていただけませんか。

    ことだ sounds like you are giving a lecture or authoritative advice. To a teacher, it sounds very rude. Use a polite request like ていただけませんか instead.

  • Using the past tense to mean 'should have'.

    もっと勉強したことだ。
    もっと勉強すればよかった / 勉強すべきだった。

    ことだ is for future-oriented advice. To express regret about the past, use patterns like 〜ばよかった or 〜べきだった.

How It Connects

Tap a pattern to see what it builds on and what it leads to.

ことだLevel 3Should, Must

Learn This First

To understand 'ことだ' (should/must), you first need to know how to turn verbs into nouns using 'こと' and how to modify nouns with verbs. Since the pattern functions as a definitive statement of advice, knowledge of the copula 'だ' is also required.

Words in This Pattern

事