IN the literature on moral progress, a central philosophical puzzle relates to how large-scale behavioral change occurs. What explains the end of slavery, reductions in poverty, extensions of liberty, and increased respect for animals and nature? Philosophers have long believed that pure reasoning is key. The articulation of abstract principles and rational arguments helps to reveal inconsistencies and falsehoods in the status quo, counteract unruly sentiments, and open our minds to new possibilities. 1 To the extent that moral beliefs guide moral action, the hope of moral progress is grounded in the acquisition of true moral beliefs.

This hope, however, has been confounded by historians and social psychologists. It has been confounded not because moral beliefs are motivationally insufficient for right action; right action, as many philosophers readily concede, requires both right reason and motivation. Rather, hope has been confounded because pure reasoning fails to supply true moral beliefs and counteract unruly sentiments in a reliable fashion. The historical record suggests that moral reasoning, far from preventing phenomena such as the Holocaust, racism, and human chauvinism, has actively rationalized them.