The Japanese noun '理性 (りせい)' refers to 'reason' or 'rationality'. It is used to describe the human capacity for logical thinking, judgment, and decision-making, often in contrast to emotions or instincts. This word is commonly used in philosophical, psychological, or everyday contexts to discuss rational thought. For example: He acted based on reason「彼は理性に基づいて行動した」(かれはりせいにもとづいてこうどうした). Losing reason in anger is dangerous「怒りで理性を失うのは危険だ」(いかりでりせいをうしなうのはきけんだ). The word can also imply self-control or the ability to think calmly and logically.
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