This chapter examines the sentence in the Critique of Practical Reason in which Immanuel Kant explicitly discusses the Groundwork of the Metaphysics of Morals and its relation to the new book. In a surprising reversal towards the end of the deduction section of the Critique of Practical Reason, Kant tells one that the 'vainly sought deduction of the moral principle' is replaced by another deduction, namely the deduction of freedom. Kant never quite identifies freedom and the fact of reason, which is the awareness of the authority of the moral law. He returns to the role of morality as the ratio cognoscendi of freedom and accords the support freedom receives from these quarters the status of a deduction. In a striking note from the Duisburg papers, Kant explicitly turns to the task of a 'critique of practical reason'.

Immanuel Kant's late work, The Metaphysics of Morals, is treated as a kind of retreat from the critical self-limitation to a formal ethics that characterises the Groundwork of the Metaphysics of Morals. In the Critique of Pure Reason, Kant made it clear that the idea of a metaphysics of morals represents a Platonism of practical reason. In this chapter, the author focuses on the Preface and on one or two specific passages from the main text of the Groundwork that expressly pursue the argument in the Preface concerning the necessity for such metaphysics. Kant's speculative arguments concern the systematic structure of philosophy and the articulated presentation of its relevant objects. His arguments concern the way in which Kant's position coincides with the understanding that everyone already possesses concerning morality. The author elucidates these arguments and questions whether it is really necessary to provide a metaphysical grounding of ethics at all.