This thesis argues that what distinguishes all major, categorical types of human societal organization is the underlying logic operant in the unstated, dynamic ruleset that determines whether social entities and social actions at any given scale of analysis are accounted for as legitimate, or illegitimate. These are here termed “logics of legitimation,” and it is argued that all of the features said to distinguish modern society from the prior historical era by theorists such as Weber, Durkheim, Marx, and Foucault can be understood as expressions of a logic of legitimation centered on systematicness, which is the cumulative effect of the mutually-reinforcing, interacting operation of six quietly operating principles that every societal feature distinctive to the modern era exemplifies one or more of at a time. After a delineation of the areas of overlap and divergence between this central claim and core tenets of the neoinstitutionalist school, it is supported by using (a) the systems logic of legitimation, (b) it’s complex of underlying principles, and (c) it’s bright contrast with the preceding “sovereignty” logic of legitimation to analyze and make sense of historically recent macroinstitutional changes in Western society that have occurred in three major domains: economics, politics, and culture. Since the concept of “modernity” is both a theoretical abstraction and a historical time-marker, the task of this thesis is only completed with a final substantive section that attempts to mark the origins of the systems logic of legitimation’s emergence in the historical chronology of Western societal evolution. The account is suggestive of potential mechanisms for the shift from one logic to another, which warrant future research. The concluding sections suggest research designs for verifying the theory here espoused, and potential applications in the studies of international geopolitics, gender, and race.