Leibniz et le principe d'inertie

It is commonly admitted that the principle of inertia has played an important role in the construction of classical mechanics. To date, much attention has been drawn to Descartes and Newton, who have afforded the principle the status of Lex Prima. However, Leibniz's views concerning the principle of inertia are less known and deserve attention. It is interesting to examine how the principle of inertia has been received by Leibniz, whose methods and orientations in the philosophy of nature are quite different from those of Descartes and Newton. The thesis of this essay is that the principle of inertia has in the philosophy of Leibniz the status of an abstraction rather than that of a law of nature and that it plays an important role in the construction of the concepts of his dynamics. In order to defend this point of view, some chapters of Leibniz's essay Dynamica de potentia will be examined closely and especially the last one dealing with the collision phenomena.;There are five chapters in the essay. The first two deal with the way Descartes and Newton have introduced the principle in their major works and the role they provided for it. The explanatory function of the principle is also examined through their respective explanation of the circular motion. The aim of the third chapter is to examine closely the difference between the principle of inertia and the concept of natural inertia often used by Leibniz. The fourth chapter deals with the way Leibniz introduced and used the principle of inertia in his physics. A particular emphasis is put on the demonstration Leibniz presents of the principle of inertia and its geometric properties. Attention is also given to the way Leibniz uses the principle of inertia as a basic element in the a priori construction of the principle of conservation of energy. The last chapter deals with the way Leibniz uses the inertial motion, which he calls motus simpliciter simplex, as a building block to reconstruct more complex motions such as the circular motion and the motion of an agregate of bodies.;Key-words. Leibniz, Descartes, Newton, philosophy, inertia, motion, Nature, principle, potentia, construction, dynamics.