Over the last 20 years, a number of central figures in moral philosophy have defended some version of moral rationalism, the idea that morality is based on reason or rationality (e.g., Gewirth 1978, Darwall 1983, Nagel 1970, 1986, Korsgaard 1986, Singer 1995; Smith 1994, 1997). According to rationalism, morality is based on reason or rationality rather than the emotions or cultural idiosyncrasi...