Translation guide
The English word "irrational" covers a range of meanings from illogical thinking to unreasonable behavior. In Japanese, different words and phrases are used depending on whether you mean contrary to logic, emotionally driven, or mathematically irrational. This guide helps you choose the most natural expression.
Describing thoughts, arguments, or decisions that lack logical basis.
The most direct and common translation for 'irrational' in the sense of being illogical or not based on reason. Used in both formal and everyday contexts.
His argument is irrational.
I oppose the irrational decision.
Literally 'non-logical'. Emphasizes a lack of logical structure. Slightly more formal and often used in academic or technical discussions.
That conclusion is irrational.
A common colloquial phrase meaning 'doesn't make sense' or 'unreasonable'. Used in everyday speech to describe something that defies logic.
His behavior is irrational.
Describing actions, demands, or people that are excessive, unfair, or driven by emotion rather than reason.
Conveys a strong sense of unreasonableness and unfairness, often with emotional weight. Commonly used when someone is being unreasonable or making excessive demands.
The boss's demands are irrational.
Means 'absurd' or 'unreasonable', often implying recklessness. Used in casual contexts to describe extreme or irrational actions.
Means 'emotional'. When someone is acting irrationally due to emotions, this adjective is often used. It implies a lack of rational control.
She had an irrational reaction.
Referring to numbers that cannot be expressed as a simple fraction, like π or √2.
不合理 (fugōri) focuses on logical inconsistency, while 理不尽 (rifujin) emphasizes unfairness and emotional unreasonableness. Use 不合理 for flawed arguments, and 理不尽 for unreasonable demands or treatment.
The phrase 'irrational fear' is often translated as 不合理な恐怖, but a more natural expression is 根拠のない恐怖 (fear without basis) or simply 恐怖症 (phobia) if it's a specific phobia.
I got scolded for an irrational reason.
That's an irrational plan.