Immanuel Kant long sought to write a metaphysics of nature. In a 1765 letter to Johann Heinrich Lambert, Kant reported that he was postponing the general project he had been working on, the “Proper Method of Metaphysics.” He would instead produce the paired “Metaphysical Foundations of Natural Philosophy” (metaphysische Anfangsgründe der natürlichen Weltweisheit) and “Metaphysical Foundations of Practical Philosophy” (der praktischen Weltweisheit) (Br, 10:56; see Förster 1989, 289–90) as particular examples in concreto of the proper philosophical methodology. Despite Kant’s claim that the “content” of these projects was “already worked out,” they were, in turn, deferred and subsequently shelved during his writing of the Inaugural Dissertation (MSI) and the subsequent tumult to his metaphysical outlook left in its wake. Nonetheless, Kant still harbored ambition to write a metaphysics of nature, expressing his hope to return to this project in the preface of the 1781 first edition of the Critique of Pure Reason while acknowledging that a critique of reason must antecede his metaphysical ambitions: “[The] Metaphysics of Nature … will be not half so extensive but will be incomparably richer in content than this critique, which had first to display the sources and conditions of its possibility, and needed to clear and level a ground that was completely overgrown” (KrV, Axxi). With the foundation for the metaphysics of nature thus laid bare with the completion of the Critique of Pure Reason, Kant embarked on writing the Metaphysical Foundations of Natural Science (Metaphysische Anfangsgründe der Naturwissenschaft), finally published in 1786, over twenty years after he mentioned the project to Lambert.

The General Remark to the Dynamics (hereafter, “the Remark”), appended to the second chapter of Kant’s MAN (4:523–35), is a perplexing tract. Therein, Kant offers a quadripartite characterization of the “specific variety of matter” – that is, those properties that vary among bodies, such as density, cohesion, aggregative state, friction, elasticity, and chemical affinity – that is bookended by reflections on his preference for a force-based methodology for explaining natural phenomena, which he dubs the “metaphysical-dynamical mode of explanation” (4:525). These considerations, particularly the discussion of the specific variety of matter, appear prima facie divorced from priorities of MAN. In MAN, Kant’s primary intention is to found the a priori part of the natural science of matter, or what he elsewhere calls the “metaphysics of corporeal nature” (4:470, 472, 478) and “rational physics” (KrV, A846/B874).1 In the body of the book, he thus proffers purportedly a priori clarifications, propositions, and laws that hold universally of all matter. To wit, among other propositions, he demonstrates that matter possesses two fundamental forces, the repulsive (MAN, 4:497) and attractive forces (4:508–9); that it is infinitely divisible (4:503–4); and that action and reaction are equal and opposite in the communication of motion (4:543–7).