This book is about the nature of scientific theory. The central topicic of inquiry concerns how it is that theories are able to supply us with powerful and elegant explanations of puzzling phenomena that often confront the scientist and layman alike. It is argued that an answer to this question supplies us with an account of how theories achieve a variety of tasks such as the prediction and organization of data, including how they support a very important class of claims known int he literature as counterfactual conditionals. The book begins by presenting a critical survey of past, classic...