Early modern probabilism was a novel and controversial doctrine in Catholic moral theology: while traditional Catholic theology was concerned with affirming absolute and certain moral rules, probabilism stressed the uncertainty and fallibility of all human knowledge and ethical systems. I propose to write the first comprehensive study of early modern probabilism and of its historical, political, and cultural implications. By combining a substantial amount of previously unpublished archival material, a diverse and interdisciplinary array of secondary sources, and the theoretical insights of critical theory and hermeneutics, my project demonstrates the historical significance and the long-lasting impact that early modern probabilism had on Western ethics, politics, and epistemology.