Autonomy and heteronomy: Kant on freedom, natural necessity, and the limits of moral philosophy (Immanuel Kant)

Kant claims that the freedom of the will is nothing other than autonomy, i.e., moral self-legislation. But this should not be taken to mean that only a morally good will can be free: moral self-legislation is not a property exclusive to morally good wills, but is rather a property of all morally obligated wills. Kant claims that all his predecessors failed to recognize that obligation is based on such self-legislation. Rather than viewing the will as autonomous or self-legislating, they all viewed the will as heteronomous---as subject to a moral law legislated by God, nature, society, etc. The root of this failure is the propensity of our reason to go beyond its own proper sphere in its attempt to explain the possibility of moral obligation. Such an explanation would have to conform to the conditions of the possibility of our experiencing the will's causality in acting morally---and the will can be experienced only as acting according to natural necessity. For Kant, such an explanation is rooted in a transcendental illusion of reason that makes it impossible either (1) to assert the will's freedom or (2) to properly formulate the moral law. Only by restraining reason from such an explanation can the will be understood as subject to law and yet free.