判断・推量N2
〜に違いない
must be... / certainly...
Structure
普通形/N + だ + に違いない
Explanation
A strong inference based on evidence: must be, certainly. Slightly more formal than に決まっている. Attached to the plain form of verbs/adjectives or noun + だ.
Examples
あの車は高いに違いない。見た目が高級だ。
That car must be expensive—it looks luxurious.
彼はもう帰ったに違いない。電気が消えているから。
He must have gone home already—the light is off.
Note
Synonymous with に相違ない. Compared with に決まっている, it emphasizes inference based on objective evidence.