Abstract

Moral rationalism is identified as the view that moral constraints are rational constraints. This view seems implausible to many because it seems to involve belief in the fantastic-sounding possibility of egoist-conversion: that, in principle, an argument for moral constraints could be produced which would motivate a rational person who does not yet accept those constraints to observe them. Furthermore, the Humean want-belief model of motivation---the view that beliefs alone are incapable of motivating---seems to provide a good explanation for the impossibility of egoist-conversion. I argue that the moral rationalist is not in fact committed to the possibility of egoist-conversion, and that an explanation of its impossibility can be given which is compatible with rationalism; so this impossibility counts neither against rationalism nor for the want-belief model. I consider a number of apparent objections to my position and rebut them.