In the intriguing epilogue to The Invention of Autonomy, J. B. Schneewind distinguishes two very different conceptions of the aim of moral philosophy. For us, he tells us, the dominant conception is likely to be the one that traces its origins back to Socrates' quest for definitions of the virtues – or more precisely, to Socrates' claim that without such definitions, the moral beliefs held by his interlocutors lacked rational grounding. Moral philosophy thus proceeds from the thought that we are not in contact with moral truth until we have found a set of moral beliefs that could be given a systematic philosophical justification. Thus, according to this view, moral philosophy is just an ongoing Socratic search – not necessarily for definitions of the virtues, but certainly for some kind of rationally grounded answer to the question of how we ought to live.

However, Schneewind shows us, a very different view has enjoyed considerable influence throughout the history of philosophy, and especially in the early modern period. According to this second view, the question of how to live has been definitively answered by Judeo-Christian revelation: the ethical claims implicit in the Bible have already shown us what we ought to do. Moral philosophy, then, cannot search for some new set of moral principles, assuming, as Socrates seems to, that the true set of principles is yet to be found.