Translation guide
Expresses certainty or lack of doubt. The most natural Japanese equivalents depend on the context: whether you are stating a fact, expressing personal conviction, or emphasizing that something is definitely true.
Expressing that something is certainly true or will definitely happen, often modifying a verb or adjective.
That's certainly true.
Literally 'without mistake', used as an adverb meaning 'without doubt' or 'undoubtedly'. Stronger than 確かに.
間違いなく彼が勝つだろう。
He will undoubtedly win.
それは間違いなく事実だ。
That is without doubt a fact.
Means 'without fail' or 'always'. Used for things that are certain to happen, often with a sense of obligation or inevitability.
Used at the beginning of a sentence or as a standalone phrase to emphasize the truth of a statement.
Formal/literary phrase meaning 'without doubt'. Often used in writing or formal speech.
疑いなく、これが最善の方法だ。
Without doubt, this is the best method.
Can also be used as a sentence adverb, meaning 'undoubtedly' or 'without a doubt'.
間違いなく、彼は天才だ。
Without a doubt, he is a genius.
Literally 'without room for doubt'. Very formal and emphatic.
疑う余地なく、彼の功績は大きい。
Without a shadow of a doubt, his achievements are great.
Expressing personal certainty or conviction about something.
Pattern meaning 'must be' or 'I'm sure that...'. Expresses strong conviction based on reasoning.
彼は成功するに違いない。
I have no doubt he will succeed.
それは本当に違いない。
I'm certain that's true.
Casual pattern meaning 'it's obvious that...' or 'of course...'. Conveys strong certainty, often in spoken Japanese.
彼が一番に決まっている。
Without doubt, he's the best.
Means 'I am convinced' or 'I firmly believe'. More formal and explicit about personal conviction.
私は彼の無実を確信している。
I am without doubt that he is innocent.
Describing something as certain, unquestionable, or indisputable.
確かに (tashika ni) is often used to agree with a statement or acknowledge a fact, similar to 'certainly' or 'indeed'. 間違いなく (machigai naku) is stronger and emphasizes that there is no mistake, closer to 'undoubtedly' or 'without fail'.
確かに、それは一理ある。
Certainly, that makes sense.
間違いなく、彼が犯人だ。
Without doubt, he is the culprit.
Avoid directly translating 'without doubt' as 疑いなしに (utagai nashi ni) in most contexts. While grammatically possible, it sounds unnatural and is rarely used. Use the options above instead.