Recent philosophical research on normativity has clarified the nature and dynamics of social norms. Social norms are distinguished from legal and moral norms on the basis of their scope, their grounds, their characteristic forms of accountability, or some combination of these features. Because of their distinct character, social norms can reinforce practical prescriptions, prohibitions, and permissions provided to particular actors by legal or moral norms. They also can conflict drastically with those prescriptions, prohibitions, and permissions resulting in serious practical dilemmas. (...) The identification of normative principles capable of resolving practical dilemmas arising from conflicts between different kinds of norms is a major aim of contemporary moral and political philosophy. This dissertation contributes to this aim by establishing the significance of conflicts between social norms and legal or moral norms during mass atrocities and liberalizing political transitions. The dissertation argues that social norms, and changes in social norms, are critical components of accurate descriptions and responsible evaluations both legal and moral of the actions of individuals and groups before, during, and after mass atrocities. The dissertation contends, further, that distinct principles of justice may apply to transitional efforts by non-state actors to transform social norms in societies recovering from large-scale crimes. Three principal results follow from this dissertations effort to integrate the conceptual framework of social norms into the study of mass atrocity. First, the dissertation clarifies and extends the historiographical thesis of norm transformation, according to which participation by ordinary individuals in mass atrocities is at least partially explained by transformations in basic norms that structure social and political life. Second, the dissertation identifies a novel basis on which to apportion legal and moral accountability for mass atrocities between individuals and groups or collectivities i.e. on the basis of the specific contributions of social norms. Third, the dissertation provides new support for the disputed claim that distinct principles of justice apply to the various actors involved in liberalizing political transitions. (shrink)