Non Adimpleti Contractus and a Problem of Overinclusiveness in International Law

This article discusses the problem of diversification of grounds for treaty suspension in international law, focusing specifically on exceptio non adimpleti contractus (exception of non-performance), which is a defence allowing the party to refuse the performance of an obligation under the legal instrument if the other party has not performed its respective reciprocal obligation. In contrast to the leading opinion, exceptio non adimpleti contractus not only exists in public international law but also creates a tangible problem of its overinclusiveness. In conjunction with clearly formulated grounds for treaty suspension in treaty law and the law of state responsibility, exceptio non adimpleti contractus enables States to extricate themselves from inconvenient treaty obligations without the burden of stiff limitations of binding rules of international law. The fluidity of exceptio non adimpleti contractus is aggravated by the fact that very few cases of its application by States have been evaluated by international tribunals. This allows States to overindulge in applying it as an unjustified means of last resort. A commonly used normative approach will not help in treating legal loopholes like the one represented by exceptio non adimpleti contractus. This article posits that the most practical strategy to tackle the problem of overinclusiveness of international law is to rely on ‘reversible rewards’ or ‘sticks and carrots’ found at the intersection of international law and behavioural economics.