  Le Grand’s extensions to Descartes’s physics included phenomena now classified as metallurgy, entomology, botany, biology, physiology, medicine, psychology, and psychiatry. Part II of the Entire Body of Philosophy, entitled The History of Nature, catalogues and critically discusses the latest experiments of his time, as well as the theories of the ancients and moderns. Prominent in his discussions is the importance of secondary causes in nature (both exemplary and secondary efficient causes), and the need for experiments, not just as tools of confirmation, but also as a means of discovering the true nature of things. This was due to his application of mechanism to explain not only the behavior of material bodies but also the entire institution of nature. Le Grand believed that God laid down the laws of nature and the principles of being by acting as the primary efficient cause, and that the operation of these laws and principles manifested themselves in nature in the form of secondary causes and effects.  Although the laws and their specific mechanisms of operation are not visible, secondary causes and their effects are. These causes and effects then are known by experience and are the starting point of all science, which is characterized by reasoning from effects (observed in nature) to causes (first principles discerned by reason). Part III of the Entire Body of Philosophy, entitled A Dissertation of the Want of Sense and Knowledge in Brute Animals, extends Descartes’s treatment of the mechanization of the soul. Le Grand provides detailed accounts of sensory and motor mechanisms to explain animal movement as the foundation of Cartesian psychology (Hatfield, 2013)