1.
must be; there is no doubt that; certainly
Expresses strong conviction or certainty about something. Attaches to verbs (plain form), adjectives, and nouns (+に). More formal than ～に決まっている and softer than ～はずだ.
Common patterns
Attaches to the plain form of verbs and i-adjectives, na-adjectives (+に/だったに), and nouns (+に/だったに).
- Verb: 降っているに違いない (it must be raining)
- i-adj: 高いに違いない (it must be expensive)
- Noun: 学生に違いない (must be a student)
Usage
Expresses the speaker's strong belief based on evidence or reasoning. Unlike ～はずだ, which is based on logical expectation, に違いない conveys personal conviction. Often used when drawing conclusions from observable facts.