Kant's Transition Project and Late Philosophy: Connecting the Opus postumum and Metaphysics of Morals by Oliver Thorndike (review)

In the autumn of 1798, at the frail age of 74, Kant indicates in letters to friends that his philosophical project still awaits completion. This concerns "the transition from the Metaphysical Foundations of Natural Science to physics, for otherwise there would be a gap in the system of critical philosophy." Kant discusses this issue in many fragments of this period, drafts that have come to be seen as part of Kant's last major project, known as Opus postumum. Comprising several hundred pages, the original manuscript was first published in 1882 (by Rudolf Reicke), and only in 1993 in English (by Eckart Förster and Michael Rosen). The precise nature of the gap and the transition meant to bridge it has remained a matter of controversy. Kant himself announces in the Critique of Pure Reason the next steps of critical philosophy, a metaphysics of morals and a metaphysics of nature. To this we need to add the third Critique. But nowhere in the first Critique, nor in these other works, is there any mention of a gap. At first sight, the claim of a gap seems incomprehensible: critical philosophy deals in all its branches, including that developed in the Metaphysical Foundations of Natural Science, with a priori principles (of pure theoretical and practical reason, of pure aesthetic and teleological judgment, of scientific reasoning). But the gap in question opens up between the a priori and the empirical realm—why should it be a task of philosophy to transit to actual physics? According to some (for example, Bryan Hall), the gap is implicit in the first Critique, in the differing notions of substance Kant employs in the A and B versions of the First Analogy: individual physical objects versus the one unchanging quantum of "substance." The second notion necessitates the ether theory Kant "deduces" in the Opus postumum, a topic only summarily dealt with in the Metaphysical Foundations. There are other important interpretations of the Opus postumum, for example, by Adickes, Förster, Friedmann, Emundts, Pollok, and Matthieu.

In Kant's Transition Project and Late Philosophy, Oliver Thorndike offers a fresh perspective on the topic. He identifies another transition problem, in Kant's moral philosophy, and argues for a close connection with the aforementioned transition. Against Förster and Friedmann, he argues that the Opus postumum transition problem is not a new project. It has older roots, relating not only to Kant's understanding of critical philosophy, theoretical and practical, but to his idea that philosophy is philosophia naturalis, a conception precritical Kant took over from Wolff and his school, for example, from Johann Peter Eberhard's Erste Gründe der Naturlehre, which Kant used for his physics lectures from 1755 onward. This conception stuck with Kant even after the critical turn. This historical finding will be received with sympathy by a growing number of Kant scholars who have tried to show that there are not only closer ties between early and late Kant, but also that he is much indebted to the German school of thought of his time. Like Wolff, Kant always believed that physics requires metaphysics, the latter understood as philosophia naturalis. (But note that in some passages the phrase has a different sense, referring to the a priori and the empirical principles of natural science.) Physicists "could in no way avoid metaphysical principles, [including] those that make the concept of their proper object, namely matter, a priori suitable for application to outer experience, such as the concept of motion, the filling of space, inertia, etc."; those principles could not have been empirical, for that would still require an explanation of their possibility, and we could otherwise not justify the "apodictic certainty [the physicists] ascribe to their laws of nature." The Opus postumum transition problem thus becomes the problem of the application of pure concepts and principles, which requires a schematism of the power of judgment, as Kant himself...