'If' is one of the most important and interesting words in the English language. It is used to express hypothetical thought - an essential part of human reasoning and decision making. This type of thought occurs wherever there is uncertainty, and uncertainty is everywhere in our lives. The use of conditional terms such as 'if' also distinguishes human intelligence from that of all other animals, permitting a higher level of rationality in human reasoning and decision making. Until now, such conditionals have been the subject of independent study by psychologists and philosophers. In this volume, Jonathan Evans and David Over present a new theoretical approach to understanding hypothetical thought. The book draws on studies from the psychology of judgement and decision making, as well as philosophical logic. A new volume in the acclaimed Oxford Cognitive Science series, 'If' will be an important book for both psychologists and philosophers interested in human reasoning. Advance praise for If: "This book brings together a wealth of work in cognitive psychology and will be valuable to both psychologists and philosophers. There is not, as far as I know, another book which covers this ground." Professor Dorothy Edgington, Dept of Philosophy, University of Oxford "This is a wonderful book. It is excellently written and provides convincing arguments for a new perspective on conditionals." Dr Klaus Oberauer, Department of Psychology, University of Potsdam, Germany.