Translation guide
How to express uncertainty in Japanese, from personal doubt to factual ambiguity.
The speaker does not know whether something is true or will happen.
Attach to a plain-form clause to say 'I don't know whether...'. Very common and natural.
I'm not sure whether it will rain tomorrow.
I don't know if he's coming.
Means 'uncertain' or 'unreliable'. Often used for information or memories.
That information is uncertain.
Formal/literary way to say 'not certain'. Often used with memories or facts.
His whereabouts are uncertain.
The speaker lacks confidence in their own knowledge, decision, or action.
Literally 'have no confidence'. The most direct way to say you are uncertain about your own ability or knowledge.
I'm not sure about that answer.
I'm not confident I can do it well.
Means 'I'm hesitating' or 'I can't decide'. Used when uncertain about a choice.
I'm not sure which clothes to buy.
Expresses possibility with a nuance of uncertainty. 'It might be that...'
He might have already gone home. (I'm not sure.)
Something is not clearly defined or hard to determine.
Means 'vague' or 'ambiguous'. Used for unclear statements, boundaries, or memories.
His explanation was vague.
Means 'unknown' or 'unclear'. Often used in formal contexts like news reports.
Means 'indeterminate' or 'unsettled'. Used for schedules, factors, etc.
The result of something is not guaranteed or predictable.
Literally 'don't know how it will turn out'. Very common for uncertain futures.
I don't know what the future holds.
The game could go either way.
Means 'uncertain' or 'unreliable' in a more formal sense, often for prospects.
While 不確か (futashika) directly translates to 'uncertain', it can sound stiff or literary. In casual conversation, patterns like 〜かどうかわからない or 自信がない are much more natural.
曖昧 (aimai) means 'vague/ambiguous', often for unclear expressions or boundaries. 不確か (futashika) means 'uncertain/unreliable', often for information or facts. Use 曖昧 when something is fuzzy, and 不確か when something is not confirmed.
I only have a vague memory.
原因は不明です。
The cause is unknown.
スケジュールはまだ不確定です。
The schedule is still uncertain.
経済の見通しは不確実だ。
The economic outlook is uncertain.