 Based on the work of Kepler and probably Descartes, Leibniz develops a model of planetary motion based on the conatus principle, the idea of aether and a fluid vortex. This theory is expounded in the work Tentamen de motuum coelestium causis (1689). According to Leibniz, Kepler's analysis of elliptical orbits into a circular and a radial component can be explained by a "harmonic vortex" for the circular motion combined with a centrifugal force and gravity, both of which are examples of conatus, to account for the radial motion. Leibniz later defines the term monadic conatus, as the "state of change" through which his monads perpetually advance.
