Renaissance Debates on Occult Qualities
Renaissance Debates
on Occult Qualities
from Jean Fernel to Daniel Sennert
Hiro Hirai
10 February 2026 – 6 PM (CET)
Renaissance natural philosophers and physicians engaged in intense debates on “occult qualities” at the threshold of the ‘Scientific Revolution’.
The professor of Medicine at the University of Wittenberg, Daniel Sennert (1572-1637), 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” (morbi occulti), as both issues were intertwined and fervently advanced by Jean Fernel (1497-1558) of Paris. Sennert’s lifelong quest for occult qualities and occult diseases was a critical response to Fernel’s ideas.
In the present lecture, I will first examine the discussion of Fernel as Sennert’s forerunner (section 1). Then I will look briefly at the debates after Fernel (section 2). These studies will lead to the survey of Sennert’s activity and productions (section 3), followed by the inspection of a striking case of 1610 from his university disputations (section 4).
All the analyses will contribute to a better understanding of Sennert’s preoccupation and endeavors in their historical and intellectual context.
Sennert’s research on occult diseases and occult qualities stretched from the early stages of his career to the final products of his mature period. His lifelong quest had the aim of responding to the Renaissance debates launched by Fernel.
About the Speaker ...
Hiro Hirai is an Associate Professor at the Center for Global Advanced Studies, University of Tokyo.
He specialises in Renaissance and early modern intellectual history, particularly natural philosophy, medicine, alchemy, and science-philosophy intersections. He has authored and edited numerous influential works, including Pseudo-Paracelsus: Forgery and Early Modern Alchemy, Medicine and Natural Philosophy (Brill, 2022) and contributions to the Encyclopedia of Renaissance Philosophy and the Encyclopedia of Early Modern Philosophy and the Sciences (Springer). His recent articles address Daniel Sennert and Renaissance debates on occult qualities, and chapters on Galen and Giordano Bruno in The Oxford Handbook of Galen and Pantheism and Panpsychism in the Renaissance (2024). He serves on editorial boards of Early Science and Medicine and major Renaissance philosophy reference works
