  Le Grand defended the first principles of Descartes’s philosophy with great fidelity. He held to Descartes’s views that the essence of matter is extension; that the essence of mind is thought; that material substance and mental substance are essentially, and really distinct; that mind and body interact; that while humans have souls, brutes and other living things are mere machines; and that material things operate by means of moving parts according to the laws of motion. Le Grand did not make any substantial revisions to Cartesian metaphysics. However, he did make two important contributions: first, he attempted to clarify Descartes’s account of motion which had direct consequences for the Cartesian account of matter, causation, and mind-body interaction; secondly, he extended the scope of Cartesian physics, treating such subjects as metals, plants, insects, animals, and the human body in detail. Both contributions represented important developments of the Cartesian science, away from scholastic Aristoteian science.