One of the main original aims of philosophy was to give us guidance about how to live our lives. The ancient Greeks typically assumed that a life led in accordance with reason, a rational life, would also be the happiest or most fulfilling. Ingmar Persson's book resumes this project, which has been largely neglected in contemporary philosophy. But his conclusions are very different; by exploring the irrationality of our attitudes to time, our identity, and our responsibility, Persson shows that the aim of living rationally conflicts not only with the aim of leading the most fulfilling life, but also with the moral aim of promoting the maximization and just distribution of fulfillment for all. Persson also argues that neither the aim of living rationally nor any of the fulfillment aims can be rejected as less rational than any other. We thus face a dilemma of either having to enter a retreat of reason, insulated from everyday attitudes, or making reason retreat from its aspiration to be the sole cont