Mind the gap: The determination, legality and consequences of implicit threats of force

Abstract Article 2(4) of the UN Charter prohibits the use of force in international relations and separately bans any threat of force, whether explicit or implicit. However, what constitutes an implicit threat remains ill-defined, undermining the UN Charter’s system of collective security. This article addresses the central question: How can implicit threats be more reliably identified? It begins by reviewing the incomplete work of the International Law Commission on threats of force, then develops a framework to distinguish prohibited implicit threats from permissible state behaviour. Grounded in a theoretical understanding of threats of force as forms of communication rather than action, the article offers a clear definition of implicit threats. To exemplify this definition, it adapts the approach of the Definition of Aggression resolution, enabling a more precise attribution of prima facie responsibility for implicit threats. Subsequently, the article explores possible justifications for implicit threats, identifies their legal consequences and outlines modalities for international responses to such threats. Finally, the article suggests resuming the juridical effort to progressively develop international law in this area.