E.T. Jaynes, a physicist who spent decades developing his approach to probability, presents probability theory as an extension of logic—a framework for reasoning under uncertainty rather than merely a branch of mathematics. Jaynes follows the Bayesian tradition, treating probability as degree of belief rather than limiting it to long-run frequencies. But he goes further, arguing that probability theory, properly understood, answers questions about how to reason that philosophers have struggled with for centuries. The book is both technical and polemical, as Jaynes criticizes what he sees as errors in conventional statistics. His framework has influenced fields from physics to artificial intelligence, though it remains controversial among statisticians. Jaynes writes with conviction and occasional combativeness, including historical and philosophical discussions alongside mathematical derivations. The book was incomplete at Jaynes's death and was finished from his notes by a colleague. For those willing to work through the mathematics, it offers a coherent philosophy of inference that connects probability, information theory, and physics. This is a work of intellectual ambition that rewards serious engagement.