This volume is the first systematic study of the style of reasoning specific to the field of philosophy in nineteenth-century France. The chapters analyze the often dispersed responses to the fundamental question of the division of the sciences based on the reciprocal relationships of inclusion or exclusion, of adversity or sorority, between metaphysics and the positive sciences. In line with the arrhythmic progress of the different forms of knowledge, these responses renew the Condillacian criticisms of the Cartesian order of the relationships between metaphysics and physics. Between a pronounced divorce and a successful marriage, this volume traces the philosophical history of the various attempts at divorce or union, which, as the century progressed, resulted in original hybridizations that aspired to define a new and ever-problematic “French philosophy.”