This book describes how the concept of rationality has evolved in the last decades. Since the early seventies, several experimental studies on reasoning have produced evidence that human people diverge significantly from the classical normative standards of rationality, such as deductive logic, standard probability theory and expected utility theory, failing to solve apparently simple reasoning tasks. There have been many controversies on what such experimental results on reasoning indicate about human rationality, giving rise to what has been called “the rationality debate”. In the first chapter, I provide an overview of how rationality has been studied in the field of social sciences, especially philosophy, and economics, focusing on some specific theoretical issues, such as the distinction between different types of rationality, the derivations of the norms of rationality and the functions which has been attributed to it in explaining human behaviour. In the second chapter, three well-known experiments on human reasoning are presented and then the origins of the rationality debate are described. The third chapter deals with psychological accounts of rationality, such as evolutionary and ecological theories, which are considered to be developments of Simon’s bounded rationality, taking into account both cognitive and environmental constraints when explaining how people actually reason. In the four chapter, I present the most recent approaches to rationality, particularly dual processes theories of cognition and the argumentative theory of reasoning, and then the implications that socio-cultural differences in people’s ways of reasoning may have in defining what rationality amounts to.
