While the historiography still often presents the development of military justice as a continuous and linear affirmation of monarchic power, narrative sources and judicial archives reveal, on the contrary, the failures and inability of the State to confront the realities of war and the criminality of combatants. They reveal the competition between jurisdictions and the difficulties involved in establishing a hierarchy of rights. Similarly, while the sovereigns of the Kingdom of France chose to build a system of derogatory justice, the documentation of the period bears witness to the porosity of the boundaries between military and ordinary justice, the fluidity of jurisdictions and the flexibility of practices. This article aims to contribute to the study of the genesis and ordinary workings of the regulation of the criminality of soldiers in the kingdom of France in the late Middle Ages and the early modern era, by looking back at two of the main pillars of this edifice: the well-known ‘urgent necessity’, on the one hand, and the lesser known ‘notorious negligence’, on the other. Drawing on legislative and narrative sources, as well as judicial archives, it revisits how the limits and inadequacies of this judicial system reveal the ideas it developed and the practices it generated to maintain a certain degree of efficiency, as well as the elevation of the exception into an operating principle.