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.
It is certain that he will come.
Is that information certain?
Literally 'there is no mistake'. Very common in speech to express strong certainty. Can be used as a standalone phrase.
This is certain (there's no doubt about it).
Attached to a clause to mean 'must be' or 'no doubt that'. Expresses strong conviction based on reasoning.
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.
I'm sure it'll be fine.
Expressing personal confidence or assured knowledge about something.
Literally 'have confidence'. Used when you are certain about your own ability or knowledge.
I am certain about that.
Means 'can assert/declare'. Stronger than 自信がある, used when you can state something with certainty.
I can say with certainty that it is correct.
Adverb meaning 'absolutely'. Often used with ～だ or ～と思う to emphasize certainty.
That's absolutely certain.
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.
Please check once more to be certain.
Means 'to make sure' or 'to ascertain'. Slightly more active than 確認する, often used for personal verification.
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.
It is certain that it will be sunny tomorrow. (neutral statement)
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).
There's no doubt he's the culprit.
I want to be certain of the facts.