Chemistry in Kant’s Opus Postumum

Bennett McNulty

UC Irvine

In Metaphysische Anfangsgründe der Naturwissenschaft (MAN), Kant claims that chemistry is an improper science—because it does not allow for the application of mathematics—but a rational science—because it has causal laws. The approach to chemistry to which Kant bestows this status is the phlogistic chemistry of, for instance, Georg Stahl. In Opus postumum (OP), however, Kant espouses a broadly Lavoisierian conception of the science after German sources, such as Lichtenberg, Gehler, and Girtanner, exposed him to the theory. This raises the question of whether, after his assimilation of Lavoisier’s chemical revolution, Kant maintains that chemistry is an improper, though rational, science. Henri Dussort (1956) defends a natural interpretation of Kant’s views on the new chemistry, according to which Kant was impressed by the Lavoisierian emphasis on quantitative measurements—particularly of relative density and by use of the balance. This interpretation contends that Kant believed the emphasis on quantitative measurements in Lavoisier’s chemistry made the science into a proper one (cf. Körner (1955)). In this paper, I argue against this interpretation. First, it depends upon a whiggish, inaccurate his- tory of chemistry. Quantitative measurements were common in chemistry prior to Lavoisier, and Kant was aware of this practice. Second, mere use of quantitative measurements does not make possible the application of mathematics to a proper science. For Kant, to apply mathematics to a natural science requires a priori principles for the mathematical construction of the concepts of that science. Third, though Kant shows discusses the use of the balance in OP (and the presuppositions necessary for its functioning), he offers no principles of construction for chemical phenomena. In contrast, I maintain that in OP Kant does not think of chemistry as a fundamentally different kind of science, despite some modifications in his thoughts on the content of the science. Kant’s views on chemistry in OP differ from those in MAN in two central ways: first, he replaces his old elements (e.g., phlogiston, earth, salt) with Lavoisier's (e.g., oxygen, hydrogen, nitro- gen) and, second, he claims that the elements as modifications of the aether that can be enumerated a priori. Although Kant modifies his list of elements, I argue that he continues to think of the elements in essentially the same way as in the Critical period. In both cases, he conceives of elements as the ultimate bearers of particular, fundamental causal powers and not, as Lavoisier would have it, as those substances that are unanalyzable in the laboratory. Furthermore, Kant's claim that elements are modifications of the aether can be understood as merely effecting a further unification of the science of chemistry. That is, thereby chemistry can be systematized under a single genus—the aether—instead of the five elements of the First Critique. There- fore, I contend that, despite prima facie evidence to the contrary, there is a great deal of continuity between Kant's Critical and post-Critical conceptions of chemistry. References: Dussort, H. 1956. Kant et la chimie. Revue Philosophique de la France et de L'Étranger 146: 392 – 397. Körner, S. 1955. Kant. Penguin Books.