Principles of the Theory of ProbabilityPrinciples of the Theory of Probability is a 1939 book about probability by the philosopher Ernest Nagel. It is considered a classic discussion of its subject.ReceptionThe philosopher Isaac Levi described Principles of the Theory of Probability as a well-known classic. Rudolf Carnap cites Nagel's classification of theories of probability in his paper 'The Two Concepts of Probability'.