In This Article Expand or collapse the "in this article" section Reasonableness in International Law

  • Introduction
  • In Law and International Law
  • In the Sources of International Law
  • Private International and Transnational Law

International Law Reasonableness in International Law
Giovanni Sartor, Giorgio Bongiovanni, Chiara Valentini
  • LAST REVIEWED: 25 February 2016
  • LAST MODIFIED: 25 February 2016
  • DOI: 10.1093/obo/9780199796953-0127


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. Chiara Valentini gratefully acknowledges support by the “Ramón y Cajal” fellowship (RYC-2012-12175) and the Research Project “Global Constitutionalism and Global Justice: Philosophical Foundations” (DER2013- 48066-C2-1-R) both funded by the Spanish Ministerio de Economía y Competitividad.

Reasonableness and Rationality

The standard of reasonableness is related to another standard for assessing determinations, namely, rationality. Depending on the idea of rationality to which we refer, reasonableness differs from rationality in various respects. First of all, rationality as optimality (i.e., making the best choices) can be opposed to an idea of reasonableness that also covers suboptimal determinations, as long as they result from appropriate efforts of bounded agents. Thus an economical, administrative, or political determination, while being suboptimal (a different choice would have achieved to a higher extent the goals of the decision maker), may still be reasonable or not unreasonable, being appropriate or sufficiently good in regard to the epistemic situation in which that determination was adopted. In moral and legal theories, however, the distinction between reasonableness and rationality is usually based on a different perspective, which focuses on the evaluative framework adopted by the concerned agents: the idea of reasonableness is opposed to restricted notions of rationality, such as those only including logical consistency of choices or their means-ends appropriateness relative to the current goals of the agent. In particular, reasonableness adds two related dimensions to means-end rationality: having concerns of the legitimate interests and views of others, according to justice, and engaging with all values and legitimate goals at stake, in the given social contexts.

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