'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 conditionals 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.