に相違ない
Without a doubt, Certainly, Surely, Not mistaken
Structure
［い］Adjective + （から）+ に相違ない
［な］Adjective + （である(1)）+ に相違ない
Noun + （である(1)）+ に相違ない
(1) であるから
Explanation
Much like its counterpart に違いない, the structure に相違ない is used to express strong conviction that something is 'certainly (A)' or that '(A) is surely the case'. It can be used to add weight to your own conclusions or to strongly affirm someone else's statement. While the word 相違 on its own means 'a difference' or 'a discrepancy', the phrase 相違ない is treated as a fixed expression. When paired with ない, it literally means 'there is no discrepancy', implying that something is factually certain.
に相違ない can be attached to verbs, い-Adjectives, な-Adjectives, and nouns.
- チームは毎日練習したから、必ず勝つに相違ない。Since the team practiced every day, they will certainly win.
- あの監督の新作だから、面白いに相違ない。It's that director's new movie, so it's bound to be interesting.
- ここは図書館だから静かに相違ない。This is a library, so it is undoubtedly quiet.
- それが私の探していた鍵に相違ない。That is without a doubt the key I was looking for.
You will frequently see に相違ない used after から, which emphasizes that the preceding clause is the undeniable 'reason' for (A).
- 彼女が泣いているのは、試験に落ちたからに相違ない。She's crying; it's surely because she failed her exam.
- 社長が電話に出ないのは、忙しいからに相違ない。The president isn't answering his phone. Without a doubt, it's because he's busy.
Caution
Please be aware that this grammar pattern carries a high level of formality. In most everyday situations, に違いない is the preferred and much more common expression.
Examples
この指輪は祖母の形見に相違ない。
There is no doubt that this ring is a memento from my grandmother.
彼が次期社長に内定したということに相違ないか？
Is there no doubt that he has been informally chosen as the next company president?
現場に残された足跡は犯人の物ということに相違ない。
There is no doubt that the footprints left at the scene belong to the culprit.
その事件の目撃者は、あの男に相違ない。
That man is, without a doubt, the witness to the incident.
彼の言うことは真実に相違ない。
What he is saying is, without a doubt, the truth.
これだけ練習したのだから、次の試合は勝つに相違ない。
Having practiced this much, we will win the next match, without a doubt.
この城は江戸時代に建てられたに相違ない。
There can be no doubt that this castle was built during the Edo period.
部長：「彼はまだ若いが、このプロジェクトを任せられる人材に相違ない。」
Department manager: 'He is still young, but he is certainly the right person to be entrusted with this project.' (without a doubt)
空がこんなに暗いのだから、まもなく雨が降るに相違ない。
The sky is this dark, so there is no doubt that it will rain soon.
試験に合格するためには、もっと勉強する必要があるに相違ない。
To pass the exam, it is certain that more studying is necessary. (without a doubt)
警察官：「彼が嘘をついているに相違ない。」
Police officer: 'He is surely lying.' (without a doubt)
彼が昨日休んだのは、風邪をひいたからに相違ない。
The reason he was absent yesterday is, without a doubt, because he caught a cold.