What does it mean to use someone as "a means only": rereading Kant

Debates about commodification in bioethics frequently appeal to Kant's famous second formulation of the categorical imperative, the formula requiring us to treat the rational (human) being as "an end in itself" and "never as a means only." In the course of her own treatment of commodification, Margaret Jane Radin observes that Kant's application of this formula "does not generate noncontroversial particular consequences." This is so, I argue, because Kant offers three different--and largely incompatible--interpretations of the formula. One focuses on the obligation to preserve rational willing; the second stresses respect for human (physical) dignity and integrity; the third views respect for others as "ends in themselves" as primarily involving a willingness to govern one's conduct by a procedure of impartial co-legislation. Only the third of these interpretations, I conclude, offers a reasonable and coherent approach to moral judgment about the limits of commodification.