Translation guide
How to express certainty in Japanese, from strong conviction to confident knowledge.
Expressing that you are certain about a fact or situation, without any doubt.
A common and neutral way to say something is certain or definite. Often used in the form 確かです or 確かだと思う.
彼が来るのは確かだ。
It is certain that he will come.
その情報は確かですか。
Is that information certain?
Expressing personal confidence or assured knowledge about something.
Literally 'have confidence'. Used when you are certain about your own ability or knowledge.
それについては自信があります。
I am certain about that.
Expressing the action of checking or confirming something to be certain.
The standard verb for 'confirm' or 'check'. Used when you want to be certain by verifying information.
もう一度確認してください。
Please check once more to be certain.
Both mean 'certain', but 間違いない is more colloquial and emphatic. 確かだ is slightly more formal and often used in written language. In casual speech, 間違いない is very common.
明日晴れるのは確かだ。
It is certain that it will be sunny tomorrow. (neutral statement)
明日晴れるのは間違いない！
It's definitely going to be sunny tomorrow! (emphatic)
The English phrase 'be certain' doesn't have a single direct equivalent in Japanese. Instead, choose the expression that matches the nuance: certainty about facts (確かだ), personal confidence (自信がある), or verification (確認する).
Literally 'there is no mistake'. Very common in speech to express strong certainty. Can be used as a standalone phrase.
これは間違いない。
This is certain (there's no doubt about it).
彼が犯人で間違いない。
There's no doubt he's the culprit.
Attached to a clause to mean 'must be' or 'no doubt that'. Expresses strong conviction based on reasoning.
彼は疲れているに違いない。
He must be tired (I'm certain he is).
Adverb meaning 'surely' or 'certainly'. Often used with ～に違いない or ～はずだ to strengthen certainty.
きっと大丈夫だよ。
I'm sure it'll be fine.
Means 'can assert/declare'. Stronger than 自信がある, used when you can state something with certainty.
それは正しいと断言できます。
I can say with certainty that it is correct.
Adverb meaning 'absolutely'. Often used with ～だ or ～と思う to emphasize certainty.
絶対にそうだ。
That's absolutely certain.
Means 'to make sure' or 'to ascertain'. Slightly more active than 確認する, often used for personal verification.
事実を確かめたい。
I want to be certain of the facts.