Abstract

The sixth chapter focuses on the evolution of Cartesianism in the last quarter of the seventeenth century in Leiden and Amsterdam, against the background of the emergence of alternative views in natural philosophy capable of replacing it as a dominant paradigm, namely, the experimental philosophy of Robert Boyle and the mathematical-experimental approach of Huygens and Newton. The last evolution of Cartesianism is reconstructed in this chapter by considering the ‘Cartesian empiricism’ of Burchard de Volder, and the reflections on the language of philosophy and practical disciplines by De Raey in Amsterdam, where he moved in 1669. In 1675 De Volder established the Leiden Theatrum physicum. There he performed experiments in order to teach the principles of a mechanical philosophy largely inspired by Descartes but open to the use of experimental and mathematical evidences in the formulation of natural laws. A similar approach was in fact assumed in the same years by Wolferd Senguerd, who used the Theatrum to perform experiments in pneumatics to teach some of the principles of his eclectic worldview, encompassing some Cartesian principles (such as that of the circularity of movement), but also rejecting the vortex theory. Yet, only De Volder developed a foundational theory for the basic principles of mechanicism, namely, the assumption that every phenomenon can be explained by the notions of matter and movement alone. This was the result of a movement internal to Cartesianism, as De Volder not only reacted (positively) to the emergence of an experimental-mathematical natural philosophy, but was also involved in the defence of Cartesianism against the Censura philosophiae cartesianae of PierreDaniel Huet (1689), in which Descartes’s metaphysics is rejected as inconsistent given its very foundation on doubt and cogito. The intermingling of these different issues resulted, in De Volder’s hands, in a further de-metaphysicisation of physics – as metaphysics cannot provide a justification for the laws of motion – and in the narrowing of the scope of foundationalism, which can only sanction the psychological character of clarity and distinction as a criterion for internal truth, defined in terms of indubitability only. Accordingly, for De Volder metaphysics cannot demonstrate, on a Cartesian basis, that phenomena are actually ruled by the principles of mechanism: insofar as, for him, metaphysics has a prominent reflective role, and loses its status as justification of the absolute truth of scientific statements. This process can be labelled as the transition from foundationalism to philosophy of science and does not characterise only his ‘Cartesian empiricism’. In Amsterdam, De Raey was, over the same years, developing his Cogitata de interpretatione (1692), embodying one of the first, self-standing philosophical considerations of language. Still maintaining his separation thesis, and attacking Hobbes and the radical Cartesians, in this text he aimed to clarify how words meaning sensory data and abstract notions (such as those of mathematics) can be used in philosophy. Rather than setting a method for how to use mental faculties, De Raey aimed, at the end of his career, to provide an updating of the linguistic meanings of scientific vocabulary, namely, a reflection rather than a justification of science.