Translation guide
The English word 'unpredictable' describes something that cannot be foreseen or expected. In Japanese, there is no single direct equivalent that covers all uses. The best choice depends on whether you are describing a person, an event, the future, or behavior. This guide organizes the most natural Japanese expressions by meaning.
Use when someone's actions, moods, or decisions are inconsistent and cannot be anticipated.
A common word for someone who acts on a whim, often changing their mind or mood. It can be used as a noun or na-adjective.
He is an unpredictable person.
I'm troubled by her unpredictable whims.
Literally 'impossible to predict'. More formal and direct than 気まぐれ. Often used for people whose behavior cannot be forecast.
His behavior is unpredictable.
A colloquial phrase meaning 'you never know what they'll do'. Emphasizes the potential for surprising or extreme actions.
Be careful, because that person is unpredictable (you never know what they'll do).
Means 'changeable' or 'fickle'. Focuses on the tendency to change frequently, often used for moods or weather, but can apply to people.
His moods are unpredictable (changeable).
Use when talking about situations, results, or developments that cannot be known in advance.
The most direct and neutral way to say 'unpredictable' for events. It is a verb phrase meaning 'cannot predict'.
The future is unpredictable.
The outcome of the match is unpredictable.
Means 'uncertain' or 'unreliable'. It implies a lack of certainty rather than an inability to predict, but often overlaps with 'unpredictable'.
A common colloquial phrase meaning 'you never know what will happen'. Used for situations full of uncertainty.
Literally 'can't read ahead'. Often used for situations where the future course is unclear, like in business or games.
Use when the unpredictability comes from a lack of order or consistency, often for natural phenomena or processes.
A loanword from English meaning 'random'. Commonly used in casual and technical contexts.
The results are completely unpredictable (random).
Means 'nonsense' or 'haphazard'. It implies something is arbitrary and unreliable, often with a negative nuance.
Means 'irregular'. Focuses on the lack of a fixed pattern, often used for schedules or occurrences.
While 予測不可能 (よそくふかのう) exists, it is less common and sounds stiff. Use 予測できない or 予測不能 instead for natural Japanese.
His behavior is unpredictable.
気まぐれ is best for describing a person's whimsical or capricious nature. 予測できない is more general and can apply to any event or situation. Use 気まぐれ when the focus is on the person's character, and 予測できない when the focus is on the inability to foresee outcomes.
The weather is unpredictable.
Life is unpredictable.
This industry is unpredictable.
彼の言うことはでたらめだ。
What he says is unpredictable (nonsense).
彼の訪問は不規則だ。
His visits are unpredictable (irregular).