In the past few decades, scientists of human nature--including experimental and cognitive psychologists, neuroscientists, evolutionary theorists, and behavioral economists--have explored the way we arrive at moral judgments. They have called into question commonplaces about character and offered troubling explanations for various moral intuitions. Research like this may help explain what, in fact, we do and feel. But can it tell us what we ought to do or feel? In Experiments in Ethics, the philosopher Kwame Anthony Appiah explores how the new empirical moral psychology relates to...