The discourse of constitutionalism emerged out of the entanglement of three strands: legal theory, political philosophy, and historical narratives. Its structure revolves around the tension between the counter-concepts (Gegenbegriffe) of arbitrariness (to be denounced) and constitution (to be legitimized). This book presents a threefold genealogical analysis to access the logic of Argentine constitutionalism. First, a conceptual history (Begriffsgeschichte) exposes the distance between recent narratives of the development of Argentine constitutionalism as constructed by political historians, on the one hand, and constitutional scientists, on the other. The second genealogy explores the theoretical rupture between modern law and the traditional knowledge of ius commune in the shift from arbitrium iuris to “legicentric” logic – that is, the preeminence of written law enacted by the state. The narrowing of the concept of arbitrium to arbitrariness was central to the formation of constitutional law’s conception of the political order. Finally, this rupture went hand-in-hand with the establishment of new political imaginaries, including autocratic caudillos, suggestible masas, anarchic tendencies of a people, etc. During the 19th century, these fueled the sense among the elites that a new order was needed; but they also still remain part of current narratives. Revealing these emotional imaginaries that guided, and continue to guide, constitutional practice enables a dialogue between the history of law as written by historians and as written by constitutionalists, with the purpose of understanding the recurrent crises that still afflict Argentine constitutionalism in the 21st century.