unreasonable

Unreasonable is an adjective used to describe something that lacks justification by logic, evidence, or fairness, or that is impractical or excessive. It can refer to actions, demands, policies, or beliefs that exceed what a reasonable person would consider appropriate. In everyday language, labeling a claim or request as unreasonable signals a normative judgment about its rationality, fairness, or practicality.

Etymology traces to un- plus reasonable, with roots in Old French raisonable and Latin ratio. The term appears in English from the Middle English period and has since acquired broad usage in ordinary speech as well as law and ethics. In legal contexts, phrases such as unreasonable search and seizure describe actions that fall outside accepted standards of reasonableness.

Usage notes: Unreasonable can describe both objective imprudence and subjective preferences. It is distinct from irrational, which implies a lack of coherent mental processes, and from merely excessive, which may be justified by circumstances. The adverbial form is unreasonably; the noun form is unreasonableness.

Related concepts include reasonableness, rationality, and logic; synonyms include imprudent, unwarranted, or excessive. In discourse, appeals to reasonableness are often used to evaluate decisions, policies, and behavior across legal, ethical, and practical contexts.