In this paper, I analyze a momentous change in eighteenth century French life sciences. Whereas in the first half of the century the conception of natural history as the systematic collection of facts had been most successful, at mid-century a new approach emerged. This approach was characterized by an accent on general philosophical themes rather than on observation and experiment. I study the grounds and features of this historical shift through the work of Maupertuis, who published papers in institutional (or Baconian) natural history in his early years, but then adopted a more speculative approach to the life sciences.

This paper proposes new ways of characterizing eighteenth-century French Cartesianism. Besides two widely-accepted elements—the belief in “strict mechanism” and the idea that to demonstrate in physics does not involve mathematics, but reference to mechanical models—I add two more, hitherto neglected, features. First, a strong emphasis on experimentalism, namely the view that experiments are crucial to natural-philosophical practice. Second, an epistemological thesis that I call “conjecturalism,” which consists in doubting that natural philosophy would attain an ultimate truth on the nature of things. To explore these facets of Cartesianism, I focus on the works of the Jesuit Noël Regnault.