《The Free Dictionary》曰，reasonable person，乃「A phrase frequently used in tort and Criminal Law to denote a hypothetical person in society who exercises average care, skill, and judgment in conduct and who serves as a comparative standard for determining liability」。
《The Business Dictionary》釋義更加精細，曰，reasonable person，乃「Ordinary, prudent person who normally exercises due care while avoiding extremes of both audacity and caution. Used as a test of liability in cases of negligence, this standard is not applied uniformly on all persons because varying degrees of reasonableness may be expected from a minor (infant), an adult, an unskilled person, or a professional such as a doctor. See also prudent man rule.」
又，《Wikinary》釋其義曰：「(law) A fictional person used as a comparative legal standard to represent an average member of society and how he or she would behave or think, especially in determining negligence; sometimes formulated as “a person of ordinary prudence exercising due care in like circumstances.”」。
由上言之，reasonable person乃為作參照或比較之用而假設的人，具備相應身分之人理應具備（reasonable）之素質（如謹慎、心智、能力、知識、判斷力等）。所謂「理應具備」，即以常理而論，應當具備，不求過多，亦不能過少。既依常理而論，不同類別之人，所理當具備之某一素質自然有多寡之別。譬如，一名會計師的會計知識理應比一名外行人豐富，他可以輕易判定某筆交易是否合法，但一名行外人則未必能。又如，一名正常的成人理應有毒蛇危險的常識，見到毒蛇會立刻意識到危險，但一名正常的三歲兒童則未必有此常識，見到毒蛇也未必會意識到危險。
此詞之漢譯五花八門，有「通情達理的人」、「理性自然人」、「理性人」、「合理人」、「普通正常人」等。前四個譯法均與「reasonable person」之法律含義相去甚遠，唯「普通正常人」與其法律含義相近。可惜，「普通正常人」有臃腫冗長之弊。
依愚見，「reasonable person」可以「常人」譯之。常人者，同一類別人中，謹慎、心智、能力、知識、判斷力等諸般素質為中等者也。衹要法律稍加界定，即可作法律術語使用。
Into Good Chinese 