In this book from the early 1800s, Essai Philosophique sur les Probabilités, the mathe matician Pierre-Simon de Laplace anticiped many ideas developed within the past 50 years in cognitive psychology and behavioral economics, explaining human tendencies to deviate from norms of rationality in the presence of probability and uncertainty. A look at Laplace's theories and reasoning is striking, both in how modern they seem, how much progress he made without the benefit of systematic experimentation, and the novelty of a few of his unexplored conjectures. We argue that this work points to these theories being more fundamental amd less contingent on recent experimental findings than we have thought.