Abstract

The idea that humans are prone to widespread and systematic biases has dominated the psychological study of thinking and decision-making. The conclusion that has often been drawn is that people are irrational. In recent decades, however, a number of psychologists have started to call into question key claims and findings in research on human biases. In particular, a body of research has come together under the heading of adaptive rationality. AR theorists argue that people should not be assessed against formal principles of rationality but rather against the goals they entertain. Moreover, AR theorists maintain that the conclusion that people are irrational is unsupported: people are often remarkably successful once assessed against their goals and given the cognitive and external constraints imposed by the environment. The growth of literature around AR is what motivates the present investigation, and assessing the plausibility of the AR challenge to research on human biases is the goal of this thesis. My enquiry analyses several aspects of this suggested turn in the empirical study of rationality and provides one of the first philosophically-informed appraisals of the prospects of AR. First and foremost, my thesis seeks to provide a qualified defence of the AR project. On the one hand, I agree with AR theorists that there is room for a conceptual revolution in the study of thinking and decision-making: while it is commonly argued that behaviour and cognition should be assessed against formal principles of rationality, I stress the importance of assessing behaviour against the goals that people entertain. However, I also contend that AR theorists have hitherto failed to provide compelling evidence in support of their most ambitious and optimistic theses about people’s rationality. In particular, I present a great deal of evidence suggesting that people are often unsuccessful at achieving prudential and epistemic goals and I argue that AR theorists have not made clear how, in light of this evidence, optimistic claims about human rationality could be defended.