Reasonableness in International Law

The idea of reasonableness is pervasive in law. At the domestic, international, and transnational levels, this idea assists the law in responding to the many different aspects relevant to its operation in contemporary legal systems, which are characterized by a plurality of legal sources and claims of legal protection. The legal discourse resorts to reasonableness to characterize the expectations of the parties in a contractual relationship; the patterns of conduct to be assessed in order to ascribe criminal or civil liability; the exercise of institutional power; or the use of public resources by institutions. Moreover, reasonableness provides a legal standard for balancing different normative possibilities, measures, and arguments in relation to different circumstances. The law evaluates according to determinations of reasonableness beliefs and actions (i.e., epistemic and practical choices). When reasonableness is used as a legal standard, thoughts and actions violating it, namely, “unreasonable” thoughts and actions, are viewed as legally faulty. Unreasonable choices may be subject to annulment or revision, or they may be subject to requests for compensation by the parties negatively affected by them, or lead to further sanctions. On the contrary, reasonable private and public choices may successfully withstand legal challenges, and reasonable actions may be exempted from sanction even when they cause harm to others. We may say, in a first approximation, that a reasonable decision is a decision that meets to a sufficient extent the relevant standards, which may concern both the substance of the decision or the process through which it was achieved, and may concern both means-end efficiency and moral impartiality.