 The critique of mathematical abstraction in favor of a more empirically rich matter theory, whether this is presented as deriving from natural history, chemistry, medicine, physiology or other disciplines, is also a constant in Diderot. The point we would emphasize most, however, is that this is also a speculative metaphysics. The shift from inert to active sensitivity is not experimentally grounded. That Diderot’s materialism was not strictly an outgrowth of empiricism, and/or experimentally based, as one might expect given the usually close relation between scientific practice and materialist philosophy, is also apparent in the dimensions he sometimes is willing to allow to his cosmogony of universally living matter.