The central claim in Kant’s philosophy is that our experience is somehow formatted by the nature of our understanding. Why think this is so?

In part 2, I made a general case for thinking that humans are special in that we can understand – we can explain and offer justifications. We misunderstand and get many things wrong of course, but the entire endeavor, our participation in the space of reasons, is something special and itself in need of some explanation. One general reason for thinking that our experience is shaped by our understanding is the fact of this participation: we experience reasons, and see the world in as ordered in such a way to be explicable and comprehensible. We are always acting upon or seeking after an explanation of things. It’s the human way of being. That is possible only if the content of our experience is the sort of thing that fits into explanations.

Wilfrid Sellars made a simple argument for thinking that our sense experience is mediated by concepts. He argues that, of course, we use our sensory experience to justify certain beliefs we have about the world. But the sensory experience itself, the patches and changes of color and sounds and smells and so on, cannot by themselves play any role in any justification. Sounds and smells and colors are of the wrong logical type (really, they are of no logical type at all). Sensory experiences must be turned into judgments, which can then play some role in an argument, explanation, or justification. A judgment in this case consists in applying concepts to the content of experience. Applying concepts means applying one’s mind or understanding. Therefore, there is no bare “given” that justifies our beliefs; there is only a “given” as mediated by concepts and understanding. (This constitutes Sellars’ rejection of “the Myth of the Given.”)

Now this simple argument is enough to suggest what we might call a “thin” Kantianism: that all sensory experiences involve some basic recognition, in the form of judgments, plus whatever other basic attributes are required to render sensory experiences ready to play roles in explanations or justifications. This gets us as far as Hume (though Hume did not take proper note of the role of the mind in this, so far as I can see). But Hume infamously argued that thinly-interpreted experience still falls short of being able to justify many of the foundational beliefs we have about the world. We experience bread entering our bodies, for example, and then we experience the result of being nourished. But there is nothing in that first experience, nothing in even the most careful scrutiny of bread, which suggests any causal power to make us become nourished. At most, we can witness in our experience only correlations, and never instances of causation. Similarly, we experience a hunk of bread at one time, and a very similar hunk of bread an instant later; but nothing in the content of experience compels us to conclude that the two hunks are in fact one and the same. So experience does not show the existence of substances, or objects. And as with the bread, so too with our own minds: the mere fact that there is first one experience, and later another experience, coupled with the memory of the first, does not force the conclusion that the two experiences belong to any single, enduring self.

In short, this thin Kantianism yields only discrete experiences, and never anything more than that. Nothing in the content of such thin experience justifies any conclusions about enduring things or selves or special causal connections among the objects of those experiences. At this point we have a three options. First, we could try to live as if reality is nothing but a disordered grab bag of discrete experiences. Good luck with that. Second, we could follow Hume and conclude that we have learned something about the nature of philosophical justification: namely, that it is laughably inadequate. We will continue to believe in substances and selves in on-going interaction with one another, but we will also realize that there really is no philosophical justification for these beliefs. But even Hume himself was nervous about this. For he tried to construct some natural explanation for the fact that we end up with these non-justified beliefs. He constructed a psychology in which habit (or custom) brought us to these conclusions, despite custom’s lack of any philosophical justification. He later saw (in the appendix to the Treatise) that thin Kantianism was insufficient for allowing the possibility of even this project. We can put the point this way: if only thin Kantianism is true, then there simply is not enough in the content of experience to suggest the existence of a thing that has any sort of psychology whatsoever. If thin Kantianism is true, Hume’s psychological project does not even get started. (This problem with option #2 also attends to option #1: we might try to live as if reality is a grab bag of discrete experiences, but now must also be completely mystified as to why we should ever think otherwise, even mistakenly.)

The third option is to make our Kantianism thicker. This third option means taking two steps. The first step is described by Galen Strawson in his discussion of Hume’s quandary over his account of the self:

One might say that what Hume [as he writes his Appendix] sees is that his philosophy allows (demands, constitutes) a transcendental argument in Kant’s sense, an argument of a sort strictly forbidden to empiricists. It allows an argument not just to the conclusion that there is something more to the mind than a series of experiences – for that is something he never doubted – but to the conclusion that the nature of this something more is correctly and knowably characterizable in a certain metaphysically specific (albeit extremely general) way: either as a persisting single something or as a non-single multiple thing that knowably involves real connection in a way that is not knowable given empiricist principles. (The Evident Connexion, p. 134)

So what Hume sees is that he has to posit “something more” of a self – some thingliness or capacity which at the very least can establish connections among discrete experiences so as to get Humean psychology up and running. That is the first step: posit something that invests experience with connections. But if we rest content with taking only this first step, we run into two problems. First, all we have done is to salvage Hume’s skepticism about the extent of philosophical justification. That is, we have done what is minimally required in order to become good Humean skeptics about ever obtaining philosophical justification for believing in selves, substances, and causality. Maybe that is a good place to be; Hume himself seemed content with it, overall. But many have found Hume’s skepticism intolerable, even without recognizing the nature of the problem raised in Hume’s appendix. The second problem is more serious. If Kant’s arguments toward the end of the Transcendental Analytic (the Refutation of Idealism) are sound, then we will not be able to account for even an illusory sense of self unless we also establish that there are causal connections among the objects in our experience. The “something more” Strawson says Hume sees he needs is still not yet enough, according to Kant. Hume needs also causality among the objects of his experience in order to get enough materials to construct even a seeming sense of self.

So the second step (if anyone is still with me here!) in this third option is to posit a “something more” which not only establishes basic, non-causal connections among experiences, but also enduring object-hood and causal connections among the objects of experiences. This means, in short, that when we judge experiences, we conceptualize experience as consisting in substances and causes. We do not experience merely sensations, nor merely sensations that have superficial relations to one another; we experience objects in on-going causal relations to one another. And we have this experience only because of the judgments we make, which is to say because of the concepts we apply.

For the sake of keeping things more simple, I have just followed Kant here in thinking that human experience as we know it requires conceptualizing the world in terms of substances and causes. But it may be that Kant was insufficiently thoughtful about this. (A sentence I do not write lightly.) Is it possible to have human understanding without parsing experience in this particular way? Is it not a human possibility to experience and understand the world as consisting in stable, fluid processes, with only occasional causal connections, or only mere propensities and probabilities? Might a thoroughly quantum world be understandable to humans? Right now I am not as confident as Kant in ruling out these possibilities. I agree with him that there must be “something more” in our judgments of experience to yield a world comprehensible to humans, but I am as yet agnostic about precisely what this “something more” must consist in. For now I am just calling the whatever-it-is “MATH” – since whatever it is we impose upon experience, it had better explain, at the very least, why deeply important forces and features of the world are susceptible to mathematical description, and even require math for their expression.