The table of categories does not allow us to say how we perceive a stone as such. The concepts of the pure intellect are only logical functions, not concepts of objects (P, 39). But, if we are not able to say not only that this A is the sun and this B is a stone, but also that this B is at least a body, all the universal and necessary laws that these concepts guarantee are worth nothing, because they could refer to any datum of experience. One could perhaps say that there is an A that heats up everything, whatever constraints there might be on variable B, but we still wouldn’t know what this entity is that heats things up, because variable A would remain unconstrained. The concepts of the pure intellect not only need sensible intuition, but also the concepts of the objects to which they must be applied.
The empirical concepts of sun, stone, water, and air are not very different from what the empiricists called “ideas” (of genera and species). Sometimes Kant speaks of generic concepts, which are concepts, but not in the sense in which he often calls concepts “categories,” which are indeed concepts, but of the pure intellect. Categories are extremely abstract concepts, such as unity, reality, causality, possibility, and necessity. We cannot determine the concept of horse through the application of pure concepts of the intellect. Horse is instead an empirical concept deriving from sensation, through comparison of the objects of experience.
Empirical concepts are not studied by general logic, which is not supposed to investigate “the source of concepts, or the way in which concepts have an origin, insofar as they are representations” (L I, 55, my emphasis). Nor are empirical concepts studied by critical philosophy, which deals not with “the genesis of experience, but about that which lies in experience”; of the two objects of study, “the former belongs to empirical psychology” (P, 21). We ought to say then that we arrive at the formulation of empirical concepts in ways that have nothing to do with the legislative activity of the intellect, which rescues the matter of the intuition from its own blindness. In which case we should know horses and houses either through their manifest quiddities (as occurred in the Aristotelian-Scholastic line of thought) or through a simple task of combination, correlation, and abstraction, as was the case for Locke.
There is a passage from the Logic that could confirm our interpretation:
In order to make our presentations into concepts, one must thus be able to compare, reflect, and abstract, for these three logical operations of the understanding are the essential and general conditions of generating any concept whatever. For example, I see a fir, a willow and a linden. In firstly comparing these objects, I notice that they are different from one another in respect of trunk, branches, leaves and the like; further, however, I reflect only on what they have in common, the trunk, the branches, the leaves themselves, and abstract from their size, shape, and so forth; thus I gain a concept of tree. (L, 100)
But the passage would be Lockean if a term like “understanding” were to retain what is, after all, its weak meaning of “Human Understanding.” Instead, this could not happen in the case of the mature Kant, who had already published the three Critiques. Whatever process the intellect goes through in order to understand that a willow and a linden are trees, it does not find this “treeness” in the sensible intuition. And in any case Kant has not told us why having a given intuition allows us to understand that it is an intuition of a linden tree.
Even “to abstract” in Kant doesn’t mean take from or make spring from (which would still be the Scholastic prospective), and not even construct by means of (which would be the empirical position): it is purely considering separately, it is a negative condition, a supreme maneuver of the intellect that knows that the opposite of abstraction would be the conceptus omnimode determinatus, the concept of an individual, which in the Kantian system is impossible. Sensible intuition must be worked upon by the intellect and illuminated by general or generic determinations.
The cited passage perhaps responded to necessities of didactic simplification (in a text that gathers and certainly reelaborates notes taken by others in the course of his lectures, and is approved by an already mentally weakened Kant), because it is in clear contrast with what is said two pages before: “the empirical concept derives from the senses by the comparison of objects of experience and only receives the form of universality thanks to the intellect” (L 1, 3). “Only” here appears to be a euphemism.
13.2. Judgments of Perception
When Kant dealt with empirical psychology, in the decade preceding the first Critique (and here, too, we have to rely on lectures given somewhat under constraint and transcribed by others6), he already knew that knowledge provided by the senses is not sufficient, because it is necessary for the intellect to reflect on what the senses have offered it. The fact that we believe we know things on the basis of the sole testimony of the senses depends on a vitium subreptionis: from infancy we are so used to grasping things as if they already appeared given in our intuition that we have never made an issue out of the role performed by the intellect in this process. Not being aware that the intellect is in action does not mean that it is not working. Thus, in his Logic Kant alludes to many automatisms of this kind, such as when we speak, demonstrating that we know the rules of language; and yet, if asked, we wouldn’t be able to say what they were, and maybe we wouldn’t be even able to say they exist (L, Intro. I, 13).
Today we would say that to obtain an empirical concept we must be able to produce a judgment of perception or perceptual judgment. But we understand perception as a complex act, an interpretation of sensible data that involves memory and culture and that results in our grasping the nature of the object. Kant, on the other hand, speaks of perceptio or Wahrnehmung only as a “representation with consciousness.” Such perceptions can be distinguished into sensations, which simply modify the state of the subject, and forms of objective knowledge. As such, they can be empirical intuitions, which through sensations refer to the singular object, and are still only appearances, devoid of concept and therefore blind. Or else they are imbued with concept, through a distinctive sign common to many things, a note (CRP/B: 249).
What would a perceptual judgment (Wahrnehmungsurteil) be, then, for Kant and how is it to be distinguished from a judgment based on experience (Erfahrungsurteil)? Perceptual judgments are an inferior logical activity (L, I, 57) that creates the subjective world of personal consciousness; they are judgments such as, When the sun shines on a stone it gets warm. They can also be erroneous and are in any case contingent (P, 20, 22 and footnotes). Judgments of experience, on the other hand, establish a necessary connection (for example, they assert in fact that The sun warms up the stone).7 It would seem, then, that the categorial apparatus is only involved in judgments of experience.
Why, then, are perceptual judgments “judgments”? Judgment is nonimmediate but mediated knowledge of an object: in every judgment there is a concept valid for a plurality of representations (CPR/B: 85). It cannot be denied that having the representation of the stone and its warming already represents a unification effectuated in the manifold of the sensible. To unite representations in a consciousness is already “to think” and “to judge” (P, 22), and judgments are a priori rules (P, 23), “all synthesis, without which even perception would be impossible, is subject to the categories” (CPR/B: 125). It cannot be that (as Kant says in P, 21) “the a priori principles of the possibility of all experience … are nothing other than propositions (Sätze) that subsume all perception … under those pure concepts of the understanding (Verstandesbegriffe)”. A Warnehmungsurteil is already woven, penetrated with Verstandesbegriffe. There can be no argument: recognizing a stone as such is already a perceptual judgment, a perceptual judgment is a judgment, and therefore it too depends on the legislation of the intellect. The manifold is given in the sensible intuition, but the conjunction of a manifold in general can enter into us only through an act of synthesis on the part of the intellect.8
In short, Kant postulates a notion of empirical concepts and perceptual judgment (a crucial problem for the empiricists), but he does not succeed in rescuing both from a quagmire, from the muddy terrain between sensible intuition and the legislatory intervention of the intellect. But for his critical theory this no-man’s-land cannot exist.
The various stages of knowledge, for Kant, could be represented by a series of verbalizations in the following sequence:
- This
