synthesis is completely constituted; it requires an additional contribution of the understanding for the possibility of the representation of objective unities (and not only of relations of successions or coexistence among impressions) to be justified. Without the act of thinking, objective cognition cannot be possible because there would be only a flow of separate impressions in which nothing could be distinguished as permanent, objective or unitary. The possibility of distinguishing between undetermined objects of intuition and determined objects of cognition lies in the activity of the understanding, which is responsible to provide the objectivity of the representations (Holzhey 1970, p. 219).←62 | 63→
3.2 The doctrine of the understanding
The purpose of the Transcendental Analytic is the development of a “logic of truth”, focusing on the faculty of the understanding in order to look for the principles of objectivity:
“The part of transcendental logic, therefore, that expounds the elements of the pure cognition of the understanding, and the principles without which no object can be thought at all, is transcendental analytic, and at the same time a logic of truth.” (KrV A62/B87)73
The general logic deals with the formal criteria of truth, which are universal and necessary insofar as it abstracts from its content and deals only with the form of our thought (KrV A54/B78). A criterion which is not only universal and necessary but also sufficient is not possible: a criterion, in order to be universal and necessary has to be abstract to the particular content of experience (otherwise, it would not be universal), while to be sufficient, it would have to refer to the particular content of experience (the truth or falsity of any epistemic judgement is determined by its relation to its particular content and object). Therefore, no criteria can be at the same time both universal and sufficient (KrV A59/B83–84). Still, it is possible to have universal and necessary criteria of truth in a transcendental sense: the Transcendental Analytic can be regarded as a “logic of truth” (KrV A62/B87) insofar as it provides the conditions of the possibility of judgements to be either objectively true or false. The a priori principles of the understanding are these conditions of the possibility of objects of experience, and thus, any epistemic judgement has to respect the universal and necessary rules of transcendental logic.
In order to identify the principles of the understanding it is necessary to refer to a guiding thread (Leitfaden) which is found by Kant in the forms of thinking intended as formal modalities as the basis of the judgement, deprived of all content. Kant is proceeding in this way: if thinking means judging, i.e. the process through which a predicate is attributed to a subject, then there are as many modalities of thinking as there are of the judgement. Since Kant asserts that the Aristotelian general logic is complete and conclusive, it suffices to consider it for individuating the forms of thought. The same function of the understanding is the source of the analytic unity of the judgement as well as of the synthesis of ←63 | 64→representations, thus providing a sort of universal range of the limits in which an object can be given in the experience. In the “metaphysical deduction” of the categories (KrV B159), Kant derives twelve categories from the Aristotelian table of the twelve forms of judgements, namely: unity, plurality, totality (quantity); reality, negation, limitation (quality); of inherence and subsistence, causality and dependence, community (relation), possibility-impossibility, existence-nonexistence, necessity-contingency (modality)74.
After exposing the categories Kant has to focus on their validity. The quid facti, that is the fact that such categories are these twelve, is not yet the 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