Is it legal to kill or capture and confine a person in war? This inter-disciplinary study provides a multi-faceted answer to this intractable question that concerns lawyers, social scientists, moral philosophers and most imminently, people who may be affected by war. It first clarifies the different conceptions of ‘legality’ and demonstrates how their conflations have plagued the debate on the legality of the use of force against individuals in armed conflict and occupation. It then examines the justifications for and the limits to two ‘techniques of legal reasoning’, lex specialis and systemic integration, and illustrates how these techniques have been misused in excess of their justifiable limits to establish the relationship among legal norms regulating such use of force. Recognising the limits to these ‘techniques of legal reasoning’ but unconvinced by the abandonment of a principled approach, this study deepens the enquiry by examining the ontology of such use of force and its connection with these legal norms. Drawing together two hitherto unconnected debates, one between social theorists on the ‘agent-structure’ problem and the other between traditional just war theorists and their critics on the morality of killing in war, it uncovers the distinct worldviews of these legal norms, whose conflation undermines their efficacy to achieve their respective goals. Through empirical illustration, it further demonstrates that these distinct worldviews have their roots in different material processes in society, whose reduction to the ideational construction in law can render these distinctions invisible but cannot erase them. The study concludes with a synopsis of its theoretical, methodological and practical implications on the relationships among different legal norms regulating the use of force against individuals in armed conflict and occupation.