Even for those who have struggled with Hegel long enough to discover that he is neither a positivist nor a communitarian, nor (at the other end of the spectrum) a Platonist, the fact that he also insists upon distinguishing his approach to practical philosophy from Kant's may seem deeply puzzling. After all, the two philosophers share in common the same principal opponents. Both set out to undermine the sceptic's doubts about the possibility of objective practical judgments and requirements; both in addition reject positivist derivations of law, exclusively empiricist accounts of human behaviour, and intuitionist forms of justification. The two philosophers furthermore seem to share the same conception of the conditions of human freedom. For Hegel as well as Kant, a theory of morality and political right devoted to advancing the cause of freedom must require more than just the absence of obstacles preventing the satisfaction of our animal passions. For Hegel as well as Kant, freedom requires in addition the respect of the ends we have as rational natures. We achieve this kind of freedom when our actions are motivated by the legislation of reason and when the social norms which constrain us are norms we can rationally endorse.
Despite these similarities, Hegel tells us in the Philosophy of Right that the conception of freedom he associates with Kant and discusses under the heading of “Moralität” must give way to the more adequate conception of “Sittlichkeit” or “ethical life”. It is clear that Hegel finds unacceptable what he calls the “empty formalism” of Kant's practical philosophy; it is also clear that he thinks that Kant's practical philosophy is “formal” because its supreme law or categorical imperative is an a priori law of reason. But this doesn't yet tell us why, for Hegel, these features of the Kantian approach are objectionable. In my view, we do his critique little justice if we say that it is aimed at a consequence which presumably follows from Kant's preoccupation with providing an a priori foundation for law and morality: namely, the failure to give sufficient moral weight to the empirical particulars which individuate persons and situations and need to be taken into account in the practice of moral assessment. As I shall argue below, the suggestion that Kant's formalism requires us to ignore empirical content in this way is neither plausible as a critique of Kant nor accurate as a representation of what troubles Hegel about Kant. We go more to the heart of the matter, I believe, if we say instead that Hegel is out to challenge the very distinction between the “empirical” and the “pure” or “a priori” so fundamental to both Kant's practical and theoretical philosophy. Hegel's critique of Kant's practical philosophy is an instance of his critique of Kant's idealism more generally, and of the assumptions about reason and nature upon which that idealism rests. Or so I shall argue here.