 Although most of Kant’s readers understand the property of autonomy as being a property of rational wills, some, such as Thomas E. Hill, have held that Kant’s central idea is that of autonomy is a property, not primarily of wills, but of principles. The core idea is that Kant believed that all moral theories prior to his own went astray because they portrayed fundamental moral principles as appealing to the existing interests of those bound by them. By contrast, in Kant’s view moral principles must not appeal to such interests, for no interest is necessarily universal. Thus, in assuming at the outset that moral principles must embody some interest (or “heteronomous” principles), such theories rule out the very possibility that morality is universally binding. By contrast, the Categorical Imperative, because it does not enshrine existing interests, presumes that rational agents can conform to a principle that does not appeal to their interests (or an “autonomous” principle), and so can fully ground our conception, according to Kant, of what morality requires of us.