Sennert and the Renaissance Debates on Occult Qualities and Occult Diseases

Abstract Renaissance natural philosophers and physicians engaged in intense debates on occult qualities at the threshold of the Scientific Revolution. Daniel Sennert of Wittenberg played a significant role in these debates through his assiduous research. His efforts were crystallized in two works of his mature period: an inquiry into occult qualities as the second book of his Physical Memoirs (1636); and the massive volume On Occult Diseases (1635). Indeed, the Renaissance debates on occult qualities were closely related to those of occult diseases, as both issues were intertwined and fervently advanced by Jean Fernel of Paris. Sennert’s lifelong quest for occult qualities and occult diseases was a critical response to Fernel’s ideas.