The Argumentative Structure of Kant's Metaphysical Foundations of Natural Science

one of kant’s most fundamental aims is to justify Newtonian science. However, providing a detailed explanation of even the main structure of his argument (not to mention the specific arguments that fill out this structure) is not a trivial enterprise. While it is clear that Kant’s Critique of Pure Reason (1781), his Metaphysical Foundations of Natural Science (1786), and his unpublished (and incomplete) Opus postumum should in some way constitute the core of this justification, it is less clear how each of these works does so in detail. In this paper I shall first argue that the standard view of the relationship between the Critique of Pure Reason and the Metaphysical Foundations of Natural Science (hereafter simply Metaphysical Foundations) is mistaken. I shall then present my own interpretation of how the Metaphysical Foundations contributes to the justification of Newtonian science. Finally, I shall conclude by considering an important interpretation of the argument of the Metaphysical Foundations developed by Michael Friedman. However, it is first necessary to present briefly Kant’s conception of science (in particular what conditions a body of knowledge must satisfy for Kant in order to be considered science proper) as well as Kant’s own understanding of the relevant differences between his projects in the first Critique, the Metaphysical Foundations, and the Opus postumum.

Kant’s conception of science is rather strict if measured by contemporary standards. For in the preface to the Metaphysical Foundations Kant establishes three substantive conditions that a body of knowledge must satisfy in order to be considered science proper.¹ (1) It must not consist in empirical principles, but rather must be obtained solely from pure, a priori principles;² (2) It must be apodictically certain;³ (3)⁴ It must be a systematically ordered whole (which means that its various propositions must be related as, for example, antecedents and consequents).⁵ After stating these conditions, Kant then argues that all natural science proper requires a pure part upon which its apodictic certainty is based. In other words, satisfaction of the first condition immediately implies satisfaction of the second condition as well.⁶ Accordingly, these three conditions (and the first one in particular) imply that natural science proper requires (or rather presupposes) a justification by something distinct from it that Kant calls a metaphysics of nature.⁷ But what exactly does a metaphysics of nature encompass? Kant distinguishes two different parts of the metaphysics of nature: a transcendental part and a special part. A metaphysics of nature is transcendental insofar as it concerns “the laws that make the concept of nature in general possible, even without relation to any determinate object of experience, and [insofar as it is] thus indeterminate with respect to the nature of this or that thing in the sensible world,” whereas a metaphysics of nature is special to the extent that “it is concerned with a special nature of this or that kind of thing of which an empirical concept is given, but so that except for what lies in this concept no other empirical principle is used for knowledge thereof.”⁸ In short, a transcendental metaphysics, revealing how experience in general is possible, is not supposed to presuppose an empirical concept, whereas a special metaphysics does make such an assumption insofar as it is concerned with the special natures of things.

How do the three works cited above relate to Kant’s distinction between a transcendental and a special metaphysics of nature? In the preface to the Metaphysical Foundations Kant clearly indicates that he intends the Metaphysical Foundations to constitute the special metaphysics of nature. Although he does not explicitly refer to the first Critique in the preface, it is also relatively clear that he sees it (or at least the ‘System of Pure Reason’ that Kant foresees as following upon it and as incorporating its fundamental results)⁹ as constituting the transcendental part of a metaphysics of nature.¹⁰ The Principles of Pure Understanding (‘Grundsätze des reinen Verstandes’) in the Transcendental Analytic argue for what could naturally be described as “laws...