How do theories of science progress'? What standards must be met by a scientific explanation? How can one evaluate competing theories? Since the time of Plato and Aristotle, scientists and philosophers have raised questions about the proper evaluation of scientific interpretations. This guide is an introduction to the philosophy of science, suitable for readers who may not have the extensive knowledge of formal logic or the history of the several sciences. This new edition includes an extended discussion of such recent developments and controversies as new approaches to evaluative standards and cognitive aims, scientific realism, causal theories of explanation, Bayesian theories of confirmation and the search for a non-prescriptive philosophy of science. John Losee is the author of Philosophy of Science and Historical Enquiry.