1.
no doubt, must be, certainly
Expresses strong certainty or conviction that something is true.
〜に違いない expresses the speaker's strong conviction that something is the case: 'it must be ~,' 'there is no doubt that ~.' The conviction is an inference, not direct knowledge — the speaker has reasoned from evidence and is confident of the conclusion.
Grammar: it attaches to a plain-form clause, with に before it. The に is fixed and is not the usual location or direction particle.
- Nouns: 彼に違いない
- Verbs (plain form): 知っているに違いない
- I-adjectives: 高いに違いない
- Na-adjectives: the bare stem, 静かに違いない — no な
Degrees of certainty, strongest first:
- 〜に違いない: must be — the speaker is sure
- 〜はずだ: should be — expected on the basis of a known reason or arrangement, and so it can be overturned by facts
- 〜だろう: probably — plain conjecture
- 〜かもしれない: might be — one possibility among several
Register: 違いない is neutral and common in speech and writing alike. In formal writing you may also meet 〜に相違ない, a stiffer equivalent found in legal and official documents.