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JLPT N3Modal Expressions

～に決まっている— I'm Sure It Must Be

Expresses the speaker's strong conviction that something is certainly the case, based on personal judgment or common sense. It is more subjective and emphatic than はずだ — closer to 'obviously' or 'of course'. Common in casual, assertive speech.

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Pro lessonUNIT 78 · MODAL EXPRESSIONS

Structure · 形

[Plain form (na-adj/noun without だ)] + に決まっている

Examples · 例文

  • そんな高い店、まずいわけがない。おいしいに決まっている。

    Sonna takai mise, mazui wake ga nai. Oishii ni kimatte iru.

    A place that expensive can't be bad — it's got to be delicious.

    い-adjective おいしい + に決まっている asserts strong certainty from common sense.

  • こんな時間に電話したら、迷惑に決まっているよ。

    Konna jikan ni denwa shitara, meiwaku ni kimatte iru yo.

    Calling at this hour is obviously going to be a nuisance.

    な-adjective 迷惑 (no だ) + に決まっている conveys the speaker's firm judgment.

  • 彼が犯人に決まっている。

    Kare ga hannin ni kimatte iru.

    He's definitely the culprit.

    Noun 犯人 (no だ) + に決まっている expresses the speaker's certain conviction.

Usage notes · 注意

  • Register: casual / conversational; sounds assertive or even pushy.
  • Based on the speaker's subjective certainty, not on solid evidence.
  • Note: no だ before に決まっている for nouns and な-adjectives.

Commonly confused with

The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones ～に決まっている is tested against.

vsはずだ

に決まっている is subjective, emotional certainty ('obviously!'); はずだ is a logical expectation based on reasoning or evidence and sounds more objective.

vsに違いない

に決まっている is casual and highly emphatic common-sense certainty; に違いない is a more formal, reasoned deduction ('must be').

More modal expressions

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