I recently wrote about the unity of Kant’s cognitive powers. Just now I was reading an article by Arata Hamawaki, “Cartesian Skepticism, Kantian Skepticism, and Two Conceptions of Self-consciousness”, published in The Logical Alien: Conant and his Critics, edited by Sofia Miguens. Hamawaki writes something that may seem to contradict the claims that I made in my blog post, for he insists that Kant wants to keep the faculties of sensibility and understanding apart, whereas I claimed that for Kant sensibility and the understanding could not be understood except in their interrelation. Hamawaki writes:

A central doctrinal and methodological principle of empiricism was the thesis that all of our ideas, or at least all of our simple ideas, are derived from corresponding (simple) impressions. This view implicitly denied the distinctness of the faculties that Kant thought it so important to keep distinct, for the empiricists held in effect that the inner states of sensibility were already ideas and hence that sensibility was already the faculty of understanding. That is, they held that all it takes for there to be an idea of an object, for there to be before my mind, an object to reflect upon, is for one’s sensibility to be in a particular state. (p. 154)

But in fact there is no contradiction between what I wrote and what Hamawaki writes. What I would like to do in this blog post is revisit the theme of the unity of the cognitive faculties, but this time through the lens of Hamawaki’s themes: Cartesian and Kantian scepticism, and the relation between Kant and the empiricists.

Let us start with Cartesian scepticism in its most well-known form, scepticism about the external world. The argument for such scepticism goes roughly like this:

• All that we are immediately perceptually aware of are our ideas.
• We cannot distinguish a state where our ideas more or less accurately reflect an external reality and a state where they do not reflect an external reality at all.
• Therefore, perception gives us no reason to believe in an external world.

This kind of scepticism is called Cartesian not because Descartes embraced it, but because he developed it in his Meditations and made it play a crucial philosophical role there. Descartes does not accept the argument, but he accepts the force of the argument; he presents it as a powerful argument which can only be defeated by proving that there is a God and that this God is not a deceiver.

To understand the Kantian way of looking at this argument, we should start by noticing that Cartesian external world scepticism requires two ingredients. First, it should be clear on reflection that all that we are immediately perceptually aware of are our ideas (not external objects). Second, our perceptual awareness should be such that it seems to be awareness of external objects. Without the first, there’s no reason to worry: we can claim that perception just puts us in touch with the world. Without the second, there is also no reason to worry, since in this case there would be no tendency in us to believe anything false. It is only because we seem to be in touch with a world, but are not, that a horrible scepticism looms over us. Perhaps we should go further and say that the two ingredients form an inseparable package; it is only when we embrace both of them that we can really understand the distinction between perceptual ideas ‘in the mind’ and external objects ‘outside’ in the way that Descartes understands that distinction.

Now the Kantian move here is to point out that these two ingredients, both of them essential to Cartesian scepticism, cannot in fact be coherently combined. How could it be true both that it is clear to us (after a little reflection) that we are only aware of ideas, and that it seems to us that we are aware of external objects? How could one and the same conscious episode present itself to consciousness as cut of from the world and as an awareness of the very world it presents itself as cut off from? The whole set-up seems impossible. If our ideas are merely ideas, then the notion of external objects simply drops out of our cognitive economy; but if the notion of external objects drops out, then there is no intelligible sense left in which our ideas are merely ideas, no sense in which they can be considered incomplete or falling short of the goal they themselves set. And thus Cartesian scepticism founders in incoherence.

But in so foundering, Cartesian scepticism opens the door to what we may call Kantian scepticism. (As with Descartes, Kant is not himself a Kantian sceptic.) Descartes was worried that our perceptual ideas might give an inaccurate representation of the world. But now it seems that they do not represent the world at all; not because there is no world to represent, but because our ideas are not vehicles of representation. They are just what they are; themselves; no more and no less. It is not that we might make a mistake in judging our perceptual ideas to be correct. Our perceptual ideas are not proper objects for judgement at all. So the new worry is that we seem to be incapable of world-directed thought.

Suppose Descartes, or some other rationalist, said: “Forget about perception, our grasp of the world is intellectual. I can have an idea of extended substance independent of perception.” Let’s grant this for the sake of argument. But what is now the content of the claim that these extended substances are real, that in grasping the idea of extended substance we are grasping the world? Making this claim requires the distinction between ideas and world that perception was supposed to give us; it requires something that makes sense of judging that an idea is true or false. This is why Kant states that objectively valid cognition requires objects to be given to us in intuition. It’s not that we need objects to be given to us in the sense that we need evidence before we can arrive at true judgements. It is that without a faculty of intuition, judgement cannot even be attempted, since there could be no thought that was object-directed. (Perhaps the only rationalist strategy for avoiding this Kantian conclusion is the — Spinozist? — claim that having a clear idea, judging the idea to be true, and the idea being true, are all at bottom identical. I will not here consider whether this might work.)

We can achieve a better grasp of the same point by shifting our attention to the empiricists and to Kant’s insistence on the distinction between the passivity of sensibility and the spontaneity of the understanding. For the empiricists, the fundamental case of having an idea is, as Hamawaki points out, having an impression. This is a passive affair. It is something that happens to us. We are not responsible for it. In this, an empiricist impression is, Kant would say, radically distinct from a judgement. For a judgement can be either justified or not justified; and in making (or not making) a judgement we are taking up a responsibility. It is in this sense that judgement is an act, that it is spontaneous. This should not be confused with the clearly incorrect claim that judgement is a choice; that it would also have been possible to make the opposite judgement. In judging that there is a table in front of me, I am entering the space of reasons, as Sellars would say; but this usually does not involve, and maybe never involves, a moment of choice. (A point well-known from criticisms of Pascal’s Wager.)

The radical empiricist view is that judgement or belief is of the same kind as an impression; for instance, in Hume’s claim that a belief is an especially vivid idea linked to a current impression. This is simply to give up on judgement and reasons and criticism; something that Hume is aware of, although one doubts that he thoroughly appreciates the force of his own dismissal of Reason in favour of Custom.

But perhaps a better model of cognition is available, a model that leaves the basic empiricist idea about impressions intact. It is a two-step model that proceeds as follows. First, we get impressions from sensibility, and perhaps also from the imagination when it recombines the original impressions into new ideas. Second, we judge those impression and ideas; either assenting to them or not. (This is essentially the Stoic model.) It may seem that this is what Hamawaki was describing as the Kantian position. We need sensibility to gives us impressions, and a separate faculty, the understanding, to judge those impressions. The empiricists were right as far as sensibility is concerned, but they left out an important second step.

This is completely wrong as a reading of Kant. (To be clear: it is not Hamawaki’s reading of Kant.) For to think of cognition as being a two-step affair, to have what Conant calls a layer-cake conception of human mindedness, is precisely to invite Kantian scepticism. For given that we have two entirely separate faculties, sensibility and understanding, how could be it the case that what sensibility presents to us is the right kind of item to be subjected to judgement? This is utterly mysterious; a wonderful pre-established harmony if it turns out to be the case, but hardly to be expected and at bottom impossible to understand. And of course our look at Cartesian scepticism suggests that the two separate faculties will not be able to harmoniously work together. Judgement requires that which is judged to have objective significance; to be about something, to be a representation of something that cannot be reduced to the representation itself. But impressions, as the empiricist conceives of them, are not representations. They do not point beyond themselves. They cannot be true or false, veridical or misleading, or anything else that might make them a proper subject of judgement. When judgement comes onto the stage after sensibility has been filled with content, it is already too late. Not even God-who-is-not-a-deceiver can now create the required relation between the contents of sensibility and the powers of judgement. So although Kant might hold, against Hume, that we must distinguish between sensibility and understanding, he certainly does not hold that sensibility and understanding are separate powers. Rather, they are two ‘structural moments’ within the single unified power of thought.

The Kantian solution is to claim that the understanding is already at work in sensibility. Our perceptions do represent objects; that is, they present things as falling under certain kinds of rules; and they do this because our power of rules, the understanding, is already at work in even our most simple perceptions. Here is a concrete example: when you see a mug, you are representing it to yourself as something that can be touched, handled, used in certain ways, that will remain in existence even when you are not looking, and that will respond in mug-like ways to events that befall it. And, crucially, this is the central, basic kind of seeing. It is not based on some simpler kind of seeing that is merely awareness of what later philosophers might call ‘raw sense data’. For the point we made above is that if we start from something as minimal as raw sense data, we will never be able to get to those richer kinds of experience that we actually have and without which human cognition would not be possible.

Here is a more abstract example. Kant’s point in the Second Analogy is that for our experience to be such that event A is represented as happening later than event B, is (in part) for it to be such that B and A are represented as connected by causal laws. Unless we were already conceiving of things as subject to the rules of causation, we could not have an experience of succession, but only a succession of experiences.

In conclusion. Kant tells us that it would be wrong to base human cognition on sensibility alone; wrong to base it on the understanding alone; but also wrong to base it on two separate faculties, sensibility and understanding, since if these faculties start out as separate, nothing could ever bring them together again. Rather, the core applications of sensibility require the understanding, and the core applications of the understanding require sensibility, and both of them make sense only as necessary moments within a unified faculty of cognition that strives for objective knowledge of the world.

(I say core applications because we can also investigate certain limit applications, edge cases, in which we attempt to get one of these moments in view while ignoring the other. If one attempts to see not a mug but merely one’s momentary visual field, the ‘bare sense data’, then insofar as one succeeds one is making a limit use of the sensibility. If one is engaged in what Kant calls general logic, e.g., the formal study of syllogisms irrespective of all content, then one is making a limit use of the understanding. But, as Conant argues at length in his Reply to Boyle, these are indeed limit cases for Kant, intelligible only against the background of the full-blooded use of those capacities together. And the reason they must be conceived of as limit cases is the story I’ve been telling above.)