Kant on Impenetrability, Touch, and the Causal Content of Perception

Abstract

It is well known that Kant claims that causal judgments, including judgments about forces, must have an a priori basis. It is less well known that Kant claims that we can perceive the repulsive force of bodies (their impenetrability) through the sense of touch. Together, these claims present an interpretive puzzle, since they appear to commit Kant to both affirming and denying that we can have perceptions of force. My first aim is to show that both sides of the puzzle have deep roots in Kant's philosophy. My second aim is to present three potential solutions to the puzzle, and show that each faces problems.Hume famously argues for the negative thesis that we have no genuine impression of causation, power, or force. Our idea of causation, he claims, comes merely from expectations based on constant conjunctions. As most readers understand him, Kant agrees with Hume that nothing causal can be genuinely perceived, 1 albeit while providing a different positive account of causal representations.In this paper, I present a puzzle for the received reading of Kant. In outline, the puzzle is that Kant appears to both affirm and deny that we can perceive force in external things.This puzzle runs quite deep in Kant's philosophy, but its core lies in the juxtaposition of two passages. The first passage comes from Prolegomena, where Kant says:our concepts of substance, of force, of action, of reality, etc., are wholly independent of experience, [and] likewise contain no sensory appearance whatsoever, and so in fact seem to refer to things in themselves … [Moreover, t]hey contain in themselves a necessity of determination which experience never equals. (Proleg. 4:315, see also A188/B234) 2 Kant understands perception in terms of sensory appearances (e.g., A115: 'Sense represents the appearances empirically in perception'). Therefore, if the concept of force is 'wholly independent of experience', and has 'no sensory appearance whatsoever', then it would seem that we could not, strictly speaking, ever perceive force. the first application of our concepts of quantity to matter… is grounded only on that property whereby it fills a space -which, by means of the sense of feeling, provides us with the quantity and figure of something extended, and thus with the concept of a determinate object in space, which forms the basis of everything else one can say about this thing... this substance discloses its existence to us in no other way than through that sense whereby we perceive its impenetrability, namely, feeling [das Gefühl], and thus only in relation to contact (MFNS 4:510) On the natural reading of this passage, Kant is stating that we perceive the impenetrability of matter via the sense of touch. Yet impenetrability is a force, so this statement is inconsistent with the negative Humean thesis. In addition, Kant seems to say that the feeling of impenetrability grounds the application of all quantitative concepts to matter, forming the A solution to the Perceived Force Puzzle would be of interest for three additional r...