NICK CHATER * and MIKE OAKSFORD THE RATIONAL ANALYSIS OF MIND AND BEHAVIOR ABSTRACT. Rational analysis (Anderson 1990, 1991a) is an empirical program of at- tempting to explain why the cognitive system is adaptive, with respect to its goals and the structure of its environment. We argue that rational analysis has two important implications for philosophical debate concerning rationality. First, rational analysis provides a model for the relationship between formal principles of rationality (such as probability or decision theory) and everyday rationality, in the sense of successful thought and action in daily life. Second, applying the program of rational analysis to research on human reasoning leads to a radical reinterpretation of empirical results which are typically viewed as demonstrating human irrationality. Rationality appears fundamental to the understanding of minds and be- havior. In clinical psychology, as well in the law, it appears to be of fundamental importance to be able to draw a boundary between sanity and madness, between rationality and irrationality. In economics, and increas- ingly, other areas of social science, human behavior is explained as the outcome of “rational choice”, concerning which products to buy, whom to marry, or how many children to have (Becker 1975, 1981; Elster 1986). But assumptions of rationality may go much deeper still – they seem to lie at the heart of the folk psychological style of explanation in which we describe each other’s minds and behavior (Cherniak 1986; Fodor 1987). Assumptions of rationality also appear equally essential to interpret each other’s utterances and to understand texts (Davidson 1984; Quine 1960). So rationality, in an intuitive sense, appears to be at the heart of the explan- ation of human behavior, whether from the perspective of social science or of everyday life. Let us call this everyday rationality: rationality concerned with people’s beliefs and actions in specific circumstances. In this informal, everyday sense, most of us, most of the time, are remarkably rational. In daily life, of course, we tend to focus on occa- sions when reasoning or decision making breaks down. But our failures of reasoning are only salient because they occur against the background of rational thought and behavior which is achieved with such little apparent effort that we are inclined to take it for granted. Rather than thinking of our patterns of everyday thought and action as exhibiting rationality, we Synthese 122: 93–131, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands.