Ethical concepts are, or purport to be, normative. They make claims on us: they command, oblige, recommend, or guide. Or at least when we invoke them, we make claims on one another; but where does their authority over us - or ours over one another - come from? Christine Korsgaard identifies four accounts of the source of normativity that have been advocated by modern moral philosophers: voluntarism, realism, reflective endorsement, and the appeal to autonomy. She traces their history, showing how each developed in response to the prior one and comparing their early versions with those on the contemporary philosophical scene. Kant's theory that normativity springs from our own autonomy emerges as a synthesis of the other three, and Korsgaard concludes with her own version of the Kantian account. Her discussion is followed by commentary from G. A. Cohen, Raymond Geuss, Thomas Nagel, and Bernard Williams, and a reply by Korsgaard.

Immanuel Kant's Groundwork of the Metaphysics of Morals ranks alongside Plato's Republic and Aristotle's Nicomachean Ethics as one of the most profound and influential works in moral philosophy ever written. In Kant's own words its aim is to search for and establish the supreme principle of morality, the categorical imperative. Kant argues that every human being is an end in himself or herself, never to be used as a means by others, and that moral obligation is an expression of the human capacity for autonomy or self-government. This edition presents the acclaimed translation of the text by Mary Gregor, together with an introduction by Christine M. Korsgaard that examines and explains Kant's argument.