The Antinomy of Practical Reason has received far less attention than most other sections in the Critique of Practical Reason, despite the fact that few are seriously tempted to reject its fundamental systematic and philosophical importance within Kant's practical philosophy. This comparative neglect is both unfortunate and remediable. It is unfortunate because focusing on it makes clear the conception of practical reason that Kant uses and needs to use within his practical philosophy as a whole. It is remediable because its basic features can be determined without excessive difficulty if one pays attention to the significant parallels it displays with the Critique of Pure Reason's Antinomy of Pure Reason.

In a first section, I briefly present the basic structure of the Antinomy of Pure Reason, paying special attention to the role that reason plays in generating this antinomy. In the second section, I reconstruct the Antinomy of Practical Reason with the help of several basic structural similarities that it bears to the theoretical antinomy. In a third section, I turn to several basic questions that arise with respect to the Antinomy of Practical Reason's central concept of the highest good, and use insights gained from the comparison of the theoretical and practical antinomies to develop detailed answers.

THE ANTINOMY OF PURE (THEORETICAL) REASON

In the Antinomy of Pure Reason of the Critique of Pure Reason, Kant claims that if one accepts what he calls Transcendental Realism – the view that appearances and things in themselves are identical – then reason can come into conflict with itself, because it can prove contradictory propositions with respect to certain features of the world.