This book offers a novel analysis of the widely-used but ill-understood technique of thought experiment. Thought experiment, which is a process of reasoning carried out within the context of a well-articulated imaginary scenario in order to answer a specific question about a non-imaginary situation, is extensively employed in fields as diverse as physics, computer science, law, and philosophy. The author argues that the powers and limits of this methodology can be traced to the fact that when the contemplation of an imaginary scenario brings us to new knowledge, it does so by forcing us to make sense of exceptional cases. Though primarily written for a philosophical audience, this volume is also likely to interest cognitive scientists, psychologists, and historians of science. At the present time, only two other book-length studies of this topic are available in English.