Discussions about Descartes and machines usually focus on two themes: his fruitful insights about the simple machines, which advanced the science of statics beyond the available ancient, medieval, and renaissance treatises on the subject; and his employment of a metaphorical understanding of machinery, notably clockwork, in the explication of corpuscular-mechanical natural philosophy. In the former case, his positive contribution is taken to be important but not of great relevance to his larger scientific projects. In the latter case, it is considered unfortunate that Descartes worked before the discoveries of Newton and others, who created a “classical mechanics” that allows for a better engagement with the properties of real mechanisms, of which Cartesian and Newtonian universes are allegedly both composed. However, recent research on Descartes and the history and foundations of mechanical engineering casts his theorizing about machines, and allied concepts at the center of his natural philosophy, in a more favorable light.

Actual working machines, including those known to Descartes and his contemporaries (such as clockworks, winches, and pulley systems) are composed of rigid parts (pinned together or linked with ropes and conveyor belts) maintained in constant, constrained contact, the results forming what is termed a “closed kinematic chain” in the mechanical literature. What is popularly called a “clockwork universe” in Newtonian physics – bodies operating under a force of mutual gravitation acting at a distance – does not constitute a “mechanism” in this sense. In fact, the doctrines that engineering students learn to understand how machines operate differ considerably from what gets taught under the heading of Newtonian mechanics. The special characteristics of mechanisms were lucidly isolated in the nineteenth century by Franz Reuleaux, the founder of modern machine design (Reuleaux 1876, Ferguson 1962). Reuleaux himself stressed the fact that the principles he articulated had clearly been appreciated in wholly intuitive ways by the great inventors of the past. Some of Descartes’ physical conceptions, vital to his overall natural philosophy, arguably manifest a similar grasp of machine behavior, although he experienced great difficulty in articulating such doctrines clearly. Viewed in this light, his letters on the “simple machines” of antiquity demonstrate this specialized understanding and indicate the potential role of such thinking within his wider philosophical views, where the behaviors of more complex mechanisms become central.