The sustained interdisciplinary debate about neovitalism between two Johns Hopkins University colleagues, philosopher Arthur O. Lovejoy and experimental geneticist H. S. Jennings, in the period 1911–1914, was the basis for their theoretical reconceptualization of scientific knowledge as contingent and necessarily incomplete in its account of nature. Their response to Hans Driesch’s neovitalist concept of entelechy, and his challenge to the continuity between biology and the inorganic sciences, resulted in a historically significant articulation of genetics and philosophy. This study traces the (...) debate’s shift of problem-focus away from neovitalism’s threat to the unity of science – “organic autonomy,” as Lovejoy put it – and toward the potential for development of a nonmechanististic, nonrationalist theory of scientific knowledge. The result was a new pragmatist epistemology, based on Lovejoy’s and Jennings’s critiques of the inadequacy of pragmatism’s account of scientific knowledge. The first intellectual move, drawing on naturalism and pragmatism, was based on a reinterpretation of science as organized experience. The second, sparked by Henri Bergson’s theory of creative evolution, and drawing together elements of Dewey’s and James’s pragmatisms, produced a new account of the contingency and necessary incompleteness of scientific knowledge. Prompted by the neovitalists’ mix of a priori concepts and, in Driesch’s case, and adherence to empiricism, Lovejoy’s and Jennings’s developing pragmatist epistemologies of science explored the interrelation between rationalism and empiricism. (shrink)