  Kant's early pre-Critical publications (1746-1756) are devoted primarily to solving a variety of broadly cosmological problems and to developing an increasingly comprehensive metaphysics that would account for the matter theory that is required by the solutions to these problems. Kant's first publication, Thoughts on the True Estimation of Living Forces (1746), explicitly attempts to solve the vis viva controversy, which had been hotly contested ever since Leibniz's attack on Descartes' laws of motion in the Acta Eruditorum in 1686. While Kant attempts to occupy an intermediary position between the Cartesian and Leibnizian positions by maintaining that both mv and mv² could be conserved in different contexts, what is of particular note is how his solution in Parts II and III rests on the conception of force developed in Part I. According to this conception, force is understood in terms of the activity of substances, an activity that Kant then uses to explain how the motions of bodies are generated, to solve the mind-body problem, and to account for both the possibility of other, actually existing worlds and the three-dimensionality of space.