Translation guide
This phrase is used to emphasize certainty or inevitability. In Japanese, this meaning is expressed through sentence-ending particles, adverbs, or fixed patterns rather than a direct translation.
The speaker asserts that something is definitely the case, often based on reasoning or evidence.
Attaches to the plain form of verbs, adjectives, or nouns to express strong conviction. Common in both spoken and written Japanese.
彼はきっと来るに違いない。
It is assuredly that he will come.
This must be something she left behind.
Used when the speaker believes something should be the case based on logical expectation. Slightly less forceful than に違いない.
彼はもう着いているはずだ。
He should have arrived by now.
そんなことはないはずだ。
That can't be the case.
Expresses that something is obviously or naturally the case. More colloquial than に違いない.
あのチームが勝つに決まっている。
That team is sure to win.
Formal and stiff equivalent of に違いない, used mainly in writing or official statements.
この書類は本物に相違ない。
This document is assuredly genuine.
The speaker conveys that a result is unavoidable or predetermined.
Indicates a natural conclusion or reason. Often used when explaining why something is the case.
彼は日本に10年住んでいたから、日本語が上手なわけだ。
He lived in Japan for 10 years, so it's no wonder his Japanese is good.
Expresses that a situation has been decided or will inevitably result in something. Often used for external decisions or logical outcomes.
このままだと、プロジェクトは中止になることになる。
At this rate, the project will end up being canceled.
Literally 'it is fate.' Used for dramatic or emotional emphasis on inevitability.
二人が出会ったのは運命だ。
It was fate that they met.
Using adverbs to stress certainty or truth.
Adverb meaning 'certainly' or 'indeed.' Often used to acknowledge a fact before adding another point.
確かに、それは本当だ。
Indeed, that is true.
Adverb meaning 'surely' or 'undoubtedly.' Often paired with に違いない or はずだ.
きっと成功するに違いない。
It is assuredly that you will succeed.
Adverb meaning 'without fail' or 'definitely.' Stronger than きっと, often used for promises or natural laws.
The English phrase 'it is assuredly that ...' is archaic and formal. In Japanese, there is no direct equivalent. Instead, use the patterns and adverbs above to convey certainty naturally. A literal translation like 'それは確実にそれである' would be unnatural.
に違いない expresses a strong subjective conviction, while はずだ is based on objective reasoning or expectation. Use に違いない when you are personally convinced, and はずだ when logic dictates something should be true.
彼は犯人に違いない。（直感）
He must be the culprit. (intuition)
彼はもう着いているはずだ。（時刻表から）
He should have arrived by now. (based on the schedule)
必ず約束を守ります。
I will assuredly keep my promise.