Abstract

This article addresses the problem of Jacques Rohault’s Cartesianism. It aims to enrich the current portrayal of Rohault (1618–72) as a Cartesian natural philosopher concerned with experimentation. The modern evaluation of Rohault as an experimentalist can benefit from another explanatory layer, emphasizing the mathematical physics that shapes his natural philosophy. In order to argue for this complementary account, I focus on an early episode in Rohault’s career, represented by his reply to Fermat’s attacks against Descartes’s law of refraction (1658). The source has been discussed, so far, solely as part of the dispute in optics between Fermat and the Cartesians. The reading endorsed here explores the source from a different angle, suggesting an alternative account grounded on a more contextual understanding of Rohault’s contribution to Cartesianism. More diverse dimensions of Rohault’s intellectual formation are revealed, which in turn provides a more complex picture of this strain of Cartesian natural philosophy.