How can Common Human Reason confirm the Correctness of the Deduction in Groundwork III – and Why does it Matter?

Kant claims in Groundwork IV:454 that the correctness of his complex philosophical deduction is confirmed by the ‘practical use of common human reason’. My paper discusses how this confirmation is possible, and why it is important for Kant’s project in the Groundwork. I argue that agents without philosophical training consider an intelligible standpoint, which is one of the central elements of the deduction, to be possible (i), that they take up this standpoint insofar as they reason under the idea of freedom (ii), and that they can be brought to acknowledge the higher normative authority of this standpoint (iii). Kant’s complex deduction is not alien to common agents insofar as it spells out these three elements of our ordinary understanding of metaphysics, agency, and morality. I conclude that the confirmation of the deduction by common human reason shows that even the content of Groundwork III can become popular, and can serve to inform and direct moral education and moral improvement.