How to say "irrational" in Japanese

• 不合理ふごうりCommon
  na-adjective, nounThe most literal equivalent: something that lacks logic or contradicts reason. Use it when pointing out that an argument, decision, or arrangement simply does not hold up rationally.
  間違まちがいを一度いちども認みとめないというのは不合理ふごうりである。↗

  It's absurd never to admit your mistakes.
• 理不尽りふじんCommon
  na-adjective, nounIrrational in the sense of unreasonably harsh or unfair: it describes demands, orders, or treatment that defy reason and leave the person affected feeling outraged.
• 不条理ふじょうりCommon
  na-adjective, nounEmphasizes absurdity rather than mere faulty logic: situations or circumstances that defy reason altogether, where the point is that things simply make no sense.

Use 不合理 for a plain lack of logic or reason, 理不尽 for unreasonableness that feels outrageous or unfair to the person affected, and 不条理 for absurdity — situations that defy reason altogether.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• 不合理ふごうりirrational
• 理不尽りふじんunreasonable
• 不条理ふじょうりabsurd
• わやunreasonable
• イラショナルirrational
• 無理むりirrational