modality N3 common casualpolitewritten
に違いない — must be / I'm sure ~
に違いない ・ にちがいない
Meaning
- must be ~ / I'm sure ~ / no doubt ~ — a confident conclusion the speaker is personally convinced of
Key sentence
電気が消えている。もう寝たに違いない。
The lights are off. He must have gone to bed.
Formation
| Attaches to | Form | Example |
|---|---|---|
| Verb / い-adjective (plain form) | Plain form + に違いない | 来る → 来るに違いない / 高い → 高いに違いない |
| な-adjective / Noun (drop だ) | N / な-adj + に違いない | 犯人 → 犯人に違いない / 便利 → 便利に違いない |
When: Expresses the speaker's strong personal conviction based on evidence. Somewhat emphatic and writerly; in casual speech きっと〜だろう or 〜はずだ is often used instead.
Examples
あんなに荷物が多いから、長期旅行に違いない。
With that much luggage, it must be a long trip.
彼女の顔色からして、何か知っているに違いない。
Judging by her expression, she must know something.
Easily confused with
〜はずだ はずだ is a logical expectation deduced from known facts or rules ('it should be, by reasoning'). に違いない is the speaker's firm personal conviction ('I'm sure of it') — more about confidence than cold deduction. 〜かもしれない Opposite ends of the certainty scale: かもしれない = 'might be' (low confidence), に違いない = 'must be' (high confidence). だろう だろう is a softer 'probably ~.' に違いない is markedly stronger — the speaker treats the conclusion as all but certain.
See に違いない in real sentences
Jengo shows に違いない the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.
Study it in JengoSources Compiled with reference to A Dictionary of Advanced Japanese Grammar, A Dictionary of Basic Japanese Grammar.