  Many of the philosophical issues in statistical mechanics center around the notion of probability as it appears in the theory. How are these probabilities to be understood? What justified choosing one probability distribution rather than another? How are the probabilities to be used in making predictions within the theory? How are they to be used to provide explanations of the observed phenomena? And how are the probability distributions themselves to receive an explanatory account? That is, what is the nature of the physical world that is responsible for the correct probabilities playing the successful role that they do play in the theory?