But at this point Kant has still not said how he can bind the variables: why do I perceive A as sun and B as stone? How do the concepts of pure intellect intervene to make me understand a stone as such, distinct from all the other stones in the heap, from the sunlight that heats it, and from the rest of the universe? Those concepts of the pure intellect that are the categories are too vast and far too general to enable me to recognize the stone, the sun, and the heat.
It is true that Kant assures us (CPR/B: 94) that once a list of primitive pure concepts has been drawn up, it is «easy» to add the derived and subaltern ones, but, since his task was to deal with the principles of the system rather than with the completeness of the system, he saved this integration for another work. In any case all we need do is consult the manuals of ontology and thereby nimbly subordinate the predicables of force, action, and passion to the category of causality, or the predicables of birth, death, and change to the category of modality. But even then we should still be on such a high level of abstraction that we could not say This B is a stone.
Therefore the table of categories does not allow us to say how we perceive a stone as such. Concepts of the pure intellect are only logical functions, not concepts of objects (P §39). But, if I am unable 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 the concepts of the pure intellect guarantee me are worth nothing, because they could refer to any datum of experience. Perhaps I could say that there is an A that heats everything, whatever empirical concept I may assign to B, but I wouldn’t know what this heating entity is, because I would not have assigned any empirical concept to A. Concepts of the pure intellect have need not only of sensible intuition but also of concepts of objects to which they may be applied.
The concepts of sun, stone, and air (and Kant is clear about this) are empirical concepts, and in that sense they are not very different from those that the Empiricists called «ideas» of genera and species. Kant sometimes talks of generic concepts, which are concepts, but not in the sense in which he often calls concepts the categories, which are indeed concepts, but of the pure intellect. The categories—as we have seen—are most abstract concepts, such as unity, reality, causality, possibility, necessity. The concept of horse is not determined through the application of the pure concepts of the intellect. An empirical concept derives from the sensations, through comparison with the objects of experience.
Which science studies the formation of empirical concepts? Certainly not general logic, which, according to Kant, must not investigate «the source of concepts, or the way in which concepts have their origin, insofar as they are representations…» (LI §5); however, it seems that Kant also thought that not even critical philosophy is entitled to undertake this task, since it should examine not how experience takes place (a task more for empirical psychology) but what experience contains. This point of view would be admissible only if the production of empirical concepts had nothing to do with the legislative activity of the intellect. We would have to know horses and houses either through manifest quiddity (as the Aristotelian-Scholastic school had it) or through a simple process of combination, correlation, and abstraction, which was Locke’s view.
There is a passage in the Logic that might confirm this interpretation:
[T]o form concepts from representations it is therefore necessary to be able to compare, reflect, and abstract; these three logical opera tions of the intellect, in fact, are the essential and universal conditions for the production of any concept in general. I see, for example, a willow and a linden tree. By comparing these objects, first of all, I note they are different from each other with regard to the trunk, branches, leaves, etc.; but then, on reflecting only upon what they have in common: the trunk, branches and the leaves themselves, and by abstracting from their size, their shape, etc., I obtain the concept of a tree. (LI §6)
Are we really, still, at Locke? The passage would be Lockian if words such as «intellect» retained the weak (all things considered) meaning of «Humane Understanding.» Which could not be the case for the older Kant, who had already published the three Critiques. Whatever work the intellect does to understand that a willow and a linden are trees, it does not find this «arboreality» in the sensible intuition. Without a legislative activity of the intellect, the material of intuition remains «blind.» And in any case Kant has not told us why, on having a given intuition, I understand that it is the intuition of linden tree.
On the other hand, even «abstracting» in Kant does not signify to take from, to make arise from (which would still be the scholastic perspective), and not even to construct through (which would be the empiricist position): it is pure considering-separately, it is a negative condition, it is the supreme maneuver of the intellect, which knows that the opposite of abstraction is the conceptus omnimode determinatus, the concept of an individual, which in Kant’s system is impossible: the sensible intuition must be elaborated by the intellect and illuminated by general or generic determinations.
And as a matter of fact the passage was perhaps a response to exigencies of didactic simplification—in a text that is a collection of notes taken and then certainly reelaborated by others in the course of his lessons—because it is in clear contrast with what is said two pages before (1, 3): «[T]he empirical concept derives from the senses by comparison of the objects of experience and thanks to the intellect it receives only the form of universality.»
Only?
2.4 Perceptual Judgments
When Kant dealt with empirical psychology in the decade prior to the first Critique (and here too the reference is to lessons given out of necessity and transcribed by others),12 he already knew that information provided by the senses was insufficient, because you need the intellect that reflects on what the senses have put before it. The fact we think we know things on the sole basis of the testimony of the senses depends on a vitium subreptionis: from infancy we are so used to grasping things as if they appeared to us already given in the intuition, that we have never considered the role played by the intellect in this process. Being unaware that the intellect is in action does not mean that it is not working: and so in the Logic (Intr. I) many automatisms of this kind are mentioned, as for example when we talk and therefore show we know the rules of language, but if someone asked us which rules, we would be unable to reply, and perhaps we would not even be able to say they exist.
Today we would say that to obtain an empirical concept we must be able to produce a perceptual judgment. But by perception we intend a complex act, an interpretation of sensible data that involves memory and culture and that ultimately results in the understanding of the nature of the object. On the other hand, Kant talks of perceptio or Wahmehmung only as a «representation with consciousness.» Such perceptions can be subdivided into sensations, which simply modify the state of the subject, and forms of objective knowledge. As such they can be empirical intuitions, which through the sensation refer to the singular object, and they are still appearances, devoid of concept, blind. Or they are imbued with concept, through a distinctive sign common to many things, a note (CPR/B: 249).
For Kant, then, what is a perceptual judgment (Wahmehmung-surteil) and how is it distinguishable from a judgment on the basis of experience (Ehrfahrungsurteil)? Perceptual judgments are a lower-order logical activity (LI §57) that creates the subjective world of personal consciousness; they are judgments such as When sunlight bathes a stone, the stone is heated; they can also be mistaken and are in any event contingent (P §20, §23). Judgments based on experience instead establish a necessary connection (e.g., they in fact assert, The sun heats the stone).13 It seems therefore that the categories intervene only in judgments based on experience.
But then why are perceptual judgments «judgments»? Judgment is not immediate but mediated knowledge of an object, and in all judgments we find a concept that holds good for a plurality of representations (CPR/B: 85). It cannot be denied that having the representation of the stone and its heating already represents a unification actuated in the manifold of the sensible: to unify representations in the consciousness is already «to think» and «to judge» (P §22), and judgments are a priori rules (P §23). If we were not satisfied, «all synthesis, without which even perception would be impossible, is subject to the categories» (CRP/B: 125). It cannot be that (as is said in the P
