1.
irrationality; illogicality; irrational; unreasonable
The quality of being contrary to reason or logic, or of not conforming to rational thought. Used both as a noun describing irrationality itself and as a na-adjective describing things that defy reasoning — emotions, customs, behaviors, or social structures that cannot be justified by logical analysis alone.
非合理な決定だ。
It is an irrational decision.
人間の行動には非合理な面がある。
Human behavior has its irrational side.
その制度の非合理さを多くの人が指摘している。
Many people point out the irrationality of that system.
行動経済学は、人が非合理な判断をするパターンを研究する分野だ。
Behavioral economics is a field that studies the patterns by which people make irrational judgments.
Formed from the prefix 非 (non-, un-) + 合理 (rational, reasonable). Functions both as a noun and as a na-adjective (e.g., 非合理な行動).
USAGE:
- Commonly used in academic, philosophical, and business writing, and in discussions of economics, psychology, and ethics.
- Can carry a critical nuance (非合理な慣習 — an irrational custom), but is also used neutrally to describe aspects of human nature that lie beyond pure logic.
- 不合理 is a very close synonym, often used interchangeably, though 不合理 tends to emphasize "unreasonable/unjust" while 非合理 tends to emphasize "not logical/not rational."
COMMON COLLOCATIONS:
- 非合理な行動: irrational behavior
- 非合理な判断: irrational judgment
- 非合理な制度: irrational system
- 非合理性: irrationality (as a property)
- 非合理主義: irrationalism (philosophical position)
SIMILAR WORDS:
- 不合理: unreasonable, absurd — very close synonym; often highlights injustice or absurdity
- 理不尽: unreasonable, unfair — emphasizes the unjustness toward a person
- 矛盾: contradiction — inconsistency between two things
- 論理的: logical — antonym of a sort, describing things that do follow logic
- 合理的: rational, reasonable — direct antonym