quid juris: one thing is how many and which kinds of categories they are, another is the legitimacy of their validity75. A transcendental justification is not necessary for pure intuitions, because they refer necessarily to sensible objects, given that such objects cannot be experienced without forms of sensibility. In contrast, the necessity of the reference of the categories to objects must be demonstrated: why can they not be mere forms of thinking, with no relation to objects? Why do they have an objective validity?
Showing this necessity is the aim of the famous Transcendental Deduction:
“I therefore call the explanation of the way in which concepts can relate to objects a priori their “transcendental deduction”, and distinguish this from the empirical deduction, which shows the how a concept is acquired through experience and reflection on it, and therefore concerns not the lawfulness but the fact from which the possession has arisen.” (KrV A85/B117)76←64 | 65→
I will not delve into a detailed analysis of the Transcendental Deduction77, but only provide a general overview of its main task, in order to stress its difference from the passages on schematism. The problem exposed in the Transcendental Deduction can be explained as the following: sensibility and its pure intuitions are not sufficient to justify experience and knowledge since they cannot provide a justification of the objective unity of epistemic judgements but only of succession and coexistence, although they are universal rules. Therefore, it is necessary to rely on a conceptual level able to provide such a unity that cannot be merely empirical, because otherwise, it would not constitute a level of legalities able to justify the unity of the experience and the necessity and universality of thought. Yet, the reference to the pure concepts, to categories regarded as functions of unification and conditions of the possibility of the unity of the objects of experience also is not sufficient. The conjunction of pure concepts of the understanding presupposes another unity:
“But in addition to the concept of the manifold and of its synthesis, the concept of combination also carries with it the concept of the unity of the manifold. Combination is the representation of the synthetic unity of the manifold.* The representation of this unity cannot, therefore, arise from the combination; rather, by being added to the representation of the manifold, it first makes the concept of combination possible. This unity, which precedes all concepts of combination a priori, is not the former category of unity (§ 10); for all categories are grounded on logical functions in judgements, but in these combination, thus the unity of given concepts, is already thought. The category therefore already presupposes combination. We must therefore seek this unity (as qualitative, § 12) someplace higher, namely in that which itself contains the ground of the unity of different concepts in judgements, and hence of the possibility of the understanding, even in its logical use.” (KrV B130–131)78←65 | 66→
This unity is the ‘I think’, that must join up with each representation. If there were no such synthetic unity, it would not be possible to justify the unity in experience, which would only be a flow of impressions, deprived of objectivity. To underline the qualitative and not the quantitative aspect of the synthetic unity means to underline its peculiar function in opposition to that of quantitative unity, the mathematic category of unity. To affirm that the ‘I think’ is one, does not mean that there is only one unique ‘I think’, but that it is the unity in itself, a function, an x, that must be presupposed in justifying the unity of experience: if cognition did not have a unity at its basis, the regularity of experience could not be explained at all. Kant’s well-known example of the straight line might help in elucidating his account of cognition and demonstrating how it differs from an idealistic perspective: in order to think of a line, it is necessary to “draw it in thought” (KrV B154), connecting in a particular way some parts of space. In this way, a particular synthesis produces the object (the line traced) and its concept, but this is not a mere intellectual synthesis that takes place in the inside of the understanding as an intellectual intuition: the multiplicity of intuitions, on the contrary, must always be given. In other terms, the operation’s unity of the synthesis of the multiplicity is the unity of the consciousness of the multiplicity of the intuitions: without the synthesis of the understanding, the multiplicity would not be unified in a consciousness and no object would be given. Through this example of the straight line, it is possible to understand how far Kant is from an idealistic position: cognition needs not only the activity of the understanding and its forms but also the manifold of intuitions and the forms of intuitions. As the example shows, in order to think of a line, the subject has to “draw” it in space. That is to say, categories are not the only sufficient and necessary conditions of cognition; space and time are also needed.
Moreover, it is important also to remark that the ‘I think’ is not to be viewed from an empirical-psychological level but, instead, as a transcendental principle necessary for the justification of the possibility of experience. Kant’s statement of the necessity of each representation to be guided by the ‘I think’ does not imply that the condition of the objectivity must be a clear empirical consciousness, self-consciousness:
“Now it does not matter here whether this representation be clear (empirical consciousness) or obscure, even whether it be actual; but the possibility of the logical form of all cognition necessarily rests on the relationship to this apperception as a faculty.” (KrV A117)79←66 | 67→
There is a huge difference between consciousness as self-knowledge and as a priori condition of the unity of the experience: the first, given and determined in the internal sense, is a representation; while the second, the ‘I think’: “it is the consciousness of the spontaneity of the thinking, but it does not reveal in itself an actual determined existence. This latter existence will follow from the diversity given through sensibility.” (de Vleeschauwer 1934–37, II, p. 228)80.
Differently from the empirical ‘I’, the ‘I think’ does not facilitate the knowledge of the self, but knowledge of the fact that a self is given:
“In the transcendental synthesis of the manifold of representations in general, on the contrary, hence in the synthetical original unity of apperception, I am conscious of myself not as I appear to myself, nor as I am in myself, but only that I am.” (KrV B157)81
But this reference to the ‘I think’ can also lead to ambiguities: to be aware of being, at this level of inquiry, does not mean to be conscious of one’s own personal existence, but of the fact that there is an experience. In Kant’s view, the ‘I’ of the ‘I think’ does not refer to the personal identity, but it is merely a function, a necessary unity to justify the unity of the experience.
Now, what are, then, the conditions of the unity of experience? Which faculties are implied in the process of cognition? In Kant’s words, the conditions of possibility of experience can be summarised as follows:
“There are, however, three original sources (capacities or faculties of the soul), which contain the conditions of the possibility of all experience, and cannot themselves be derived from any other faculty of the mind, namely sense, imagination, and apperception. On these are grounded 1) the synopsis of the manifold a priori through sense; 2) the synthesis of this manifold through the imagination; finally 3) the unity of this synthesis through original apperception.” (KrV A94)82←67 | 68→
It is not sufficient to claim that sensible impressions are given in sensibility according to space and time, but it is necessary to state that they are reproduced by the imagination
