Metaphysics of Nature in Kant's Opus postumum argues that Kant's last, unfinished manuscript contains an attempt to work out the long-awaited "system of pure speculative reason" or "metaphysics of nature" Kant had been promising for many years.

Challenging current readings of Opus postumum that claim to show how Kant was filling a "gap" in the Critical system, this book explores how the gap might be the system itself. Suggestive of an entirely different approach, Metaphysics of Nature in Kant's Opus postumum argues that we must develop a more radical, open-ended reading of Kant's last drafts, now known as Opus postumum (1796-1803), so as to situate them in a broader light. Thomson offers a new interpretation of the place and role of the hundreds of pages bundled into "fascicles" which Kant left on his desk when he died by taking his demand for a "metaphysics of nature" to be the seed from which they grow and the centre around which they orbit. By starting out with the often overlooked Architectonic of Pure Reason in Critique of Pure Reason, this book explores how Opus postumum is this future born into the present; it is Kant's attempt to deliver on the Critical promise of a fully worked out metaphysics of nature.