**Marij van Strien (Guest WIP)**

In this paper I examine the foundations of Laplace’s famous statement of determinism in 1814, and argue that this statement depends on Leibnizian metaphysics. Laplace wrote in 1814 that an intelligence with perfect knowledge of the present state of a system and perfect calculating capacities can predict future states with certainty. It is usually supposed that Laplace derived this statement from his physics, specifically, the statement is thought to be based on the fact that classical mechanics is deterministic: each system in classical mechanics has an equation of motion which has a unique solution. However, Laplace could not have proven this result, since it depends on a theorem about uniqueness of solutions to differential equations that was only developed later on: it was developed by Cauchy in the 1820’s and further refined by Lipschitz in 1876. (Furthermore, the theorem left open the possibility of indeterminism in systems that are not “Lipschitz-continuous”).

I argue that on the basis of his physics, Laplace could not be certain of determinism. However, I argue that there was a strong metaphysical background to Laplace’s determinism. In fact, the only motivation that he explicitly gives for his determinism is Leibniz’ principle of sufficient reason. Furthermore, Laplace was far from the first to argue for determinism, and as I show in this paper, he was also far from the first to do so in terms of an intelligence with perfect knowledge and calculating capacities. In particular, he was very likely influenced by similar statements in D’Holbach and Condorcet. The ideas of both Condorcet and D’Holbach were clearly philosophically motivated; in particular, Condorcet made an appeal to the law of continuity, which was attributed to Leibniz and in turn thought to be derived from the principle of sufficient reason. By tracing out these connections, we can understand how exactly Laplace’s determinism is supported by Leibniz’ principle of sufficient reason.