In this seminal work, Pierre-Simon de Laplace, one of history's most influential scientists, presents a profound philosophical examination of the calculus of probabilities. Beyond merely outlining mathematical concepts, Laplace delves into the epistemology of chance, the nature of certainty, and the role of probability in scientific inquiry and human reasoning. This study is not only a foundational text in the history of probability theory but also a significant contribution to the philosophy of science, exploring how we understand and quantify uncertainty in a deterministic universe. It offers timeless insights into the probabilistic nature of knowledge and decision-making.