ABSTRACT
In the Critique of Pure Reason, Kant asserts – in opposition to Hume’s empiricism – that the lawfulness of nature can be explained thoroughly, though not by means of experience alone. Experience “certainly tells us what is there, but it does not tell us what must necessarily be one way and not another” (KVR: A1). In order to explain the possibility of natural laws, Kant performs a revolutionary reinterpretation, a “Copernican Turn,” as it were. Accordingly, knowledge need not simply conform to nature; on the contrary, nature must itself, in a certain sense, conform to knowledge. The object of knowledge is understood not as something already fully determined and available for empirical assimilation; rather, it is only by means of the subject that it is …rst determined what the object is. Kant is certainly of the opinion, which he carefully outlines, that the subject is “affected” by an external “thing in itself.” However, the still chaotic sense-data which the subject receives in this way are, according to Kant, given order and form by the subject. First, they are ordered through the forms of intuition, namely space and time, which already lie in the subject and confer on the sense-data the character of spatial-temporal intuitions. The sense-data are clasped in the unity of self-consciousness to the “synthetic unity of apperception” (KVR: B131-9) and then determined further by means of the categories of the understanding which similarly already lie within the subject – categories such as “quantity,” “causality,” and “substance.” In this way, the spatial-temporal ordering of intuitions is imprinted with an additional structure. Two successive events, such as “A spark descended into the powder keg” and “An explosion occurs” are linked together by means of the category of causality, and only then can they be understood as linked with respect to a causal law: “Because a spark descended into the powder keg, therefore an explosion was triggered.” The spark is conceived as the cause and the explosion as its effect. It is only through such categorial determinations, such as that of causality, that natural being becomes available for knowledge, as for example in the aforementioned case of knowledge of causal relations. With that a principle of pure understanding is formulated which is constitutive for all experience. Accordingly, the law-like regularity of nature is essentially the result of the formative activity of the subject. This is emphasized in Kant’s famous dictum: “The understanding does
not draw its laws (a priori) from nature, but rather prescribes them to it” (PR: §36; the original text in italics). With respect to the above example, this means that any natural being which I encounter is in principle causally conditioned. Of this I am certain prior to all experience – “a priori.” Certainly, how the causal principle is realized in concrete natural laws is variable, for example as the law of gravity, as the law of the refraction of light, etc. Thus, with respect to their specific determinateness the natural laws cannot originate in the subject. Kant names the view he develops “transcendental.” The transcendental philosophy is “the system of all principles of pure reason” (KVR: B27). With that, he wants to distance himself terminologically from a philosophy which accepts any kind of transcendent authority lying “beyond,” and thus unavailable to, the subject. By contrast, according to the transcendental view the formal elements of nature reside in the subject prior to all experience: these are the forms of intuition, namely space and time, as well as the twelve categories of the understanding, which further determine the intuitions. We thus never have knowledge of “things in themselves,” that is, things “as they in themselves might be.” Rather, we have knowledge of appearances, i.e. of how things appear to us with respect to our forms of intuition and categories – whereby Kant explicitly remarks that “appearance” <Erscheinung> should not be equated with “…ction” <Schein> (KVR: B69-71). Since, however, the appearances are determined by our own forms (i.e. the forms of intuition and the categories), we can have a priori knowledge of the appearances in advance of all experience, for example that nature is constituted spatio-temporally and causally. Kant’s transcendental approach thus renders valid a priori determinations of experience, and without these the scienti…c experience of law-like regularities of nature would be impossible. The aim of the Critique of Pure Reason is to make visible such “transcendental conditions of the possibility of experience” which exist within the subject from the outset. A fundamental problem with Kant’s fascinating proposal is admittedly the concept of the thing-in-itself. This must be entirely unrecognizable, since it is in no way liable to any subjective formation. It is nevertheless constitutive of Kant’s position, for, as stated earlier, the thing-in-itself must “affect” the subject and deliver to it by means of this effect the “raw material of sensible perception.” If the spatio-temporal and categorial forms which enable knowledge lie in the subject, then, in contrast, the sensible content must originate in a thing-in-itself which, for its part, must in principle lie beyond the reach of knowledge. Nevertheless Kant argues with this concept. He attributes existence to it, characterizes it as unknowable and yet claims to know that the thing-in-itself affects the subject. That, however, means that it has an effect, and “effect” presupposes the category of causality, which sure enough has no application with respect to things-in-themselves. In short, with regard to the thing-in-itself nothing is compatible. It is thus no surprise that Fichte, who succeeded Kant and was in thorough agreement with the principle of the transcendental, set out to resolve this aporia. Though not aporetic, it is nevertheless a further serious defect that, though Kant certainly provided justi…cations within the scope of his claim, he unfortunately left
the claim itself unjusti…ed. The unaccounted assumption of a thing-in-itself is but one facet of the problem. The assumption of a priori “forms of intuition” and categories is no more justi…ed, and this leads directly to such questions as: Why are there spatial and temporal forms of intuition? Why are there forms of intuition at all, and why are there exactly two? Why does the faculty of the understanding possess categories, and why are there exactly twelve? Here, Kant himself recognized the need for an explanation and, at any rate, tried to provide a rationale. He ascribed the categories to the capacity to judge (which itself is admittedly in need of justi…cation) and sought to provide arguments for why there are exactly twelve (on this issue, see Reich 1932). Of particular signi…cance for the development of German Idealism are those observations which Kant developed under the title of a “transcendental dialectic.” With intuition attached to space and time, and the understanding grounded on the capacity to judge, Kant sees in reason the capacity to bring the rules of the understanding under a principle (KVR: A302/B359), i.e. to …nd the unconditioned for that which is conditioned in multiple respects (A307/B364) and in this way to think of an ultimate “absolute totality” (A326/B383). Such a concept, generated by reason, is called a “transcendental idea” (A311/B368) and appears concretely in three forms – soul, world and God. Since they exceed the bounds of experience, such ideas have a transcendent character and so, Kant explains, can only function regulatively, i.e. they cannot lead to “hard” empirical results but rather can only guide scienti…c research. If this restriction is not born in mind, then thought inevitably becomes ensnared in dialectical aporias, as for example in the question of whether or not the world has a beginning: as Kant demonstrated, the af…rmative and the negative response each leads to an antinomy (for critical analysis on this see Wandschneider 1989). While holding the “hard,” empirically oriented knowledge of the understanding in the highest esteem, Kant clearly also allowed for the concerns of reason and, in particular, the question concerning the unconditioned. It is with respect to the latter that Kant substantially in¶uenced the development of the “speculative” philosophy of German Idealism. (Of interest with respect to this point is Hegel’s presentation of Kant’s “critical philosophy” in the context of the “Encyclopedia,” Hegel Werke: 8.§§40-60.)
Metaphysical foundations of natural science
Published in 1786, Kant’s Metaphysical Foundations of Natural Science seeks to work out more clearly the consequences of the transcendental approach with respect to the natural sciences (here in particular see Plaass 1965; Schäfer 1966; Hoppe 1969: esp. Ch. 2; Falkenburg 1987: Ch. 2). One can only speak of a real science of nature, according to Kant, “if the natural laws, which it takes as its basis, are known a priori and not as mere laws of experience” (MA: 468). What Kant has in mind is a metaphysics of nature (469), which consequently “is drawn from the essence of thought itself and is in no way a …ctitious invention on account of not being borrowed from experience” (472). With that, Kant is thinking of the “principles of pure understanding,” such as the universal principle of causality, which were developed in the Critique of
Pure Reason under the guidance of the categories. The system of principles “provides the schema for the metaphysics of nature” (Schäfer 1966: 24) and, with that, forms the general background for the empirical science of nature. For its part, however, this assumes collaterally the empirical existence of things and the intuition thereof. It thus presupposes space and time and accordingly, as Kant emphasizes, mathematics (geometry and arithmetic) as that which is conceptually commensurate to space and time – such that “in every doctrine of nature there is only so much proper science, . . . as there is that to which mathematics is applicable” (MA 470). Mathematical physics is thus distinguished from all other natural sciences. Its fundamental concept is a concept of matter, understood as “movable in space.” This general concept, which nevertheless contains an empirical element (i.e. existence), is developed further by Kant in accordance with the categories and in a purely conceptual manner: into a pure doctrine of motion (“phoronomy”), a doctrine of the …lling of space by forces (“dynamics”), a doctrine of the interaction of material bodies (“mechanics”), and a doctrine of motion with respect to the perceiving subject (“phenomenology”). With that, the “metaphysical foundations” of natural science are delineated, though admittedly restricted to physics. Kant’s doctrine of forces was repeatedly taken up in German Idealism, whereby the spatial reality of matter was said to be constituted by the opposing forces of attraction and repulsion (MA: Ch. 2).
