Kant, Immanuel (1724–1804)

7. The principles of judgment and the foundations of science

Kant proceeds from the categories to the foundations of natural science in several steps. First, he argues that the categories, which thus far have merely logical content, must be made ‘homogeneous’ with experience, or be recast in forms we can actually experience. Since time, as the form of both outer and inner sense, is the most general feature of our sensible experience, Kant argues that the categories must be made homogeneous with experience by being associated with certain determinate temporal relations or ‘schemata’ (A 138–9/B 177–8). For example, the pure category of ground and consequence, thus far understood only abstractly as the relation of the states of objects that makes them fit to be objects of hypothetical (‘if–then’) judgments, is associated with the schema of rule-governed temporal succession, something closer to what we can actually experience. Focused as he is on the universality of time, Kant seems to de-emphasize spatiality unduly in the ‘Schematism’: for example, it would seem more natural to say that the schema of causality is the rule-governed temporal succession of states of objects within an appropriate degree of spatial contiguity.

Next, in the ‘System of all Principles of Pure Understanding’, Kant argues for the necessity of certain fundamental principles of all natural laws. Following the division of the categories, this chapter is divided into four parts. In the first, the ‘Axioms of Intuition’, Kant argues that ‘All intuitions are extensive magnitudes’ (B 202), and thus that all objects of experience are subject to the mathematics of discrete quantities. In the second, the ‘Anticipations of Perception’, Kant proves that ‘In all appearances, the real that is an object of sensation has intensive magnitude, that is, a degree’ (B 207), and is thus subject to the mathematics of continuous quantities; here he argues that because our sensations manifest varying degrees of intensity we must also conceive of the objects they represent as manifesting a reality that varies in degree. The first of these two ‘mathematical’ principles (A 162/B 201) does not add to results already established in the Transcendental Aesthetic, however, and the second depends upon an empirical assumption.

In the next section, the ‘Analogies of Experience’, dealing with the first of two kinds of ‘dynamical’ principles, Kant offers some of the most compelling and important arguments in the Critique. In the First Analogy, Kant argues that we can determine that there has been a change in the objects of our perception, not merely a change in our perceptions themselves, only by conceiving of what we perceive as successive states of enduring substances (see Substance). Because we can never perceive the origination or cessation of substances themselves, but only changes in their states, Kant argues, the sum-total of substances in nature is permanent (B 224). In the Second Analogy, Kant argues for a further condition for making judgments about change in objects: because even when we undergo a sequence of perceptions, there is nothing in their immediate sensory content to tell us that there is an objective change, let alone what particular sequence of change there is, we can only distinguish a ‘subjective sequence of apprehension from the objective sequence of appearances’ (A 193/B 238) by judging that a particular sequence of objective states of affairs, a fortiori the sequence of our perceptions of those states, has been determined in accordance with a rule that states of the second type can only follow states of the first type – precisely what we mean by a causal law. Finally, the Third Analogy argues that because we always perceive states of objects successively, we cannot immediately perceive states of two or more objects to be simultaneous, and can therefore only judge that two such states simultaneously exist in different regions of space if they are governed by laws of interaction dictating that neither state can exist without the other (A 213/B 260).

Kant’s arguments have been assailed on the basis of relativity theory and quantum mechanics. But since they are epistemological arguments that our ability to make temporal judgments about the succession or simultaneity of states of affairs depends upon our judgments about substance, causation and interaction, it is not clear that they are open to objection from this quarter. If relativity tells us that the succession or simultaneity of states of affairs may depend upon the choice of inertial frame, then Kant’s theory is not refuted, but just predicts that in that case our own judgments about temporal sequence must also vary. If quantum mechanics tells us that causal laws are merely probabilistic, then Kant’s theory is again not refuted but just predicts that in that case our temporal judgments cannot be entirely determinate.

In the last section of the ‘Principles’, Kant assigns empirical criteria to the modal concepts of possibility, actuality and necessity. The main interest of this section lies in the ‘Refutation of Idealism’ which Kant inserted into it in the second edition. Here Kant argues that temporal judgments about one’s own states require reference to objects which endure in a way that mental representations themselves do not, and therefore that consciousness of oneself also implies consciousness of objects external to oneself (B 275–6; also B xxxix–xli). There has been controversy not only about the precise steps of the proof, but also about whether it is supposed to prove that we have knowledge of the existence of things ontologically distinct from our own representations, which seems to undercut Kant’s transcendental idealism. However, the argument of 1787 was actually just the first of many drafts Kant wrote (Reflections 6311–16, 18: 606–23), and these suggest that he did mean to prove that we know of the existence of objects ontologically distinct from ourselves and our states, although we cannot attribute to them as they are in themselves the very spatiality by means of which we represent this ontological distinctness.

Finally, in the Metaphysical Foundations of Natural Science, published between the two editions of the Critique (1786), Kant carried his a priori investigation of the laws of nature one step further by introducing not only the empirical notion of change itself but also the further empirical concept of matter as the movable in space (4: 480). With this one empirical addition, he claims, he can deduce the laws of phoronomy, the vectorial composition of motions in space; of dynamics, the attractive and repulsive forces by which space is actually filled; of mechanics, the communication of moving forces; and of phenomenology, which in Kant’s sense – derived from J.H. Lambert, and very different from its later senses in Hegel or Husserl – means the laws for distinguishing apparent from real motions. This work is not an essay in empirical physics but rather an exploration of the conceptual framework into which the empirical results of physics must be fitted.