Mechanistic Philosophy and the Rejection of Aristotelian Physics

The mechanistic philosophy of nature that spread across Europe in the 17th century held that all natural phenomena, including living bodies, could in principle be explained through the size, shape, arrangement, and motion of material particles interacting by contact and impact, without recourse to the Aristotelian apparatus of substantial forms, final causes, or the four qualities (hot, cold, wet, dry) that had structured scholastic physics for centuries. René Descartes (1596–1650) provided the most systematic and influential version of this program in his Principia Philosophiae (Principles of Philosophy, 1644) and the earlier, unpublished Le Monde (The World, written by 1633 but withheld from publication after Descartes learned of Galileo's 1633 condemnation, since Le Monde likewise assumed a moving Earth). Descartes conceived the entire material universe, including animal bodies, as a single vast mechanism, a plenum of matter in constant vortical motion with no true vacuum, governed by a small number of general laws of motion he took to follow directly from God's immutability — including an early, if imperfectly formulated, statement of a principle of inertia, according to which a body in motion continues in a straight line unless acted upon by another body.