Descartes remained stuck on figures and movement. Leibniz will translate: it’s the same thing to say that nature proceeds in a curvilinear manner, or to say that beyond figures and movement, there is something that is the domain of forces. And on the very level of the laws of movement, Leibniz is going to change everything, thanks precisely to differential calculus. He will say that what is conserved is not MV, not mass and velocity, but MV2. The only difference in the formula is the extension of V to the second power. This is made possible by differential calculus because differential calculus allows the comparison of powers and of rejects . Descartes did not have the technical means to say MV2. >From the point of view of the language of geometry and of arithmetic and algebra, MV2 is pure and simple non-sense.