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.
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
Related Words
Compare:
不合理 (unreasonable, absurd)
Compare:
理不尽 (unreasonable, unfair)
Compare:
矛盾 (contradiction)
Antonym:
論理的 (logical)
Antonym:
合理的 (rational, reasonable)