namely, space and time, that are forms of the outer and the inner sense66.
In these explanations, Kant seems to be repeating the views provided in his Dissertation. However, his perspective is now significantly different: he is not trying to provide an explanation of the constitution of the world (sensible and intelligible, as in the Dissertation) but rather of the possibility of claims of objective cognition. Given the presupposition that universal and necessary propositions (the well-known synthetic a priori judgements) do exist, he aims to explain their grounds, relying on the combination of different elements and functions.
On the one hand, there is the continuous presence of an element of novelty (the content “given” in sensibility), thus providing synthetic a priori judgements with fruitfulness (they are not merely analysis, definitions, but are actually able to increase the content of cognition); on the other hand, there is the form, the way in which this novelty occurs. In this view, the distinction between sensibility and understanding does not designate two forms of experience that are completely separated, because the experience is in itself united67.
The division among faculties might be interpreted as a way to underline the peculiarity of human knowledge: there is an irreducible dualism between passivity and activity, particularity and contingency of the content, and general and universal concepts and laws. Referring to the pure elements as forms, Kant aims at underscoring how their value is not substantial but functional, as they do not consist of rules to be applied to a matter itself independent, but rather they are conditions of its very organisation. As Cohen (Cohen 1918) stresses, Kant’s pure forms can be conceived as logical conditions of experience, general methods that justify the order of the multiplicity of sensations. Moreover, two other differences from the Dissertation can be identified. Firstly, the priority given to the focus on space: although time is more general (everything is given in time but not in space), it is easier and more intuitive to represent time through space. Secondly, Kant introduces a separation between a metaphysical as well as a transcendental exposition: while the former is the clear representation of an a priori concept and aims to present and explain what space and time consist in by describing their metaphysical (non-empirical) content, the latter consists of the clarification of a ←59 | 60→principle as transcendental, that is to say a principle which is a condition of possibility of other a priori cognitions.
After illustrating the features of space and time in their Metaphysical Exposition, Kant first focuses on their Transcendental Expositions, aiming at underlying how space and time form the basis of the possibility of a priori knowledge. As he states, the basis of geometry can only be provided by pure intuition, in this case, by space: if the principle of geometry were empirical, geometry would not be universal and necessary, and if they were concepts, they would be predicable and so they would hold an extension. But if it were so, then such discursive and qualitative principles could not succeed in providing a justification for the axioms of geometry:
“That the straight line between two points is the shortest is a synthetic proposition. For my concept of the straight contains nothing of quantity, but only a quality. The concept of the shortest is therefore entirely additional to it, and cannot be extracted out of the concept of the straight line by any analysis. Help must here be gotten, by means of which alone the synthesis is possible.” (KrV B16)68
In a similar way, if we focus on the theory of motion, only time insofar as it is not a concept, rather a pure intuition, can be regarded as its fundamental principle:
“Only in time can both contradictorily opposed determinations in one thing be encountered, namely successively. Our concept of time therefore explains the possibility of as much synthetic a priori cognition as is presented by the general theory of motion, which is no less fruitful.” (KrV B49)69
Without succession no change would be possible: the passage from A to non A would be only a contradiction and the variety and multiplicity of experience could not be explained. For instance, a chrysalis turns into a butterfly only through time. Butterflies have a life cycle consisting of four stages: from egg to larva, through a chrysalis and finally to become a butterfly. Without the succession in time the progress from one stage to another could not be possible.←60 | 61→
Now, a question arises from these considerations:
“Now how can an outer intuition inhabit in the mind that precedes the objects themselves, and in which the concept of the latter can be determined a priori? Obviously not otherwise than insofar as it has its seat merely in the subject, as its formal constitution for being affected by objects and thereby acquiring immediate representation, i.e. intuition, of them; thus only as the form of outer sense in general.” (KrV B41)70
Understanding what Kant means by ‘subject’ is undoubtedly problematic. Does he refer to a psychological subject? A theoretical one? In which sense?
Kant’s inquiry concerns the conditions of possibility of knowledge and not the psychological process. For this reason, the term ‘subjective’ might here be interpreted as not objective. Forms are not objects of experience but rather belong to the subject who has experiences: they do not belong to a subject absolutely regarded as autonomous and isolated, nor to an absolute object. As Cohen interprets the notion of the form (Cohen 1918, p. 205), on the one hand it is the form of the phaenomenon, that is, the object of experience; on the other hand it belongs to the subject transcendentally intended, as the field of the object’s possible manifestation. From this perspective form is a condition that can justify the regularity of human experience, in which the contents vary, but this variation is reduced to rules. These considerations explain why space and time are endowed with empirical reality as well as transcendental ideality: they are not conditions of the possibility of things in themselves, but of things given in the experience with respect to its limits and conditions. In other words: it makes sense to apply space and time to phenomena, to objects of experience (empirical reality); but there is no sense in applying them to things in themselves, which are not and cannot be given in experience (transcendental ideality71 of pure intuitions).
If one were to claim that space and time have transcendental reality, this would imply that intuition has the capacity to bring the contingent content of experience to the existence, consequently making the contingent side of the process of knowledge (the empirical content) necessary. On the other hand, it is possible to think of an intuition that is characterised by a transcendental reality: the intuition ←61 | 62→of an understanding that is a-human, an intellectus archetypus, in which thought and being are identified. But we cannot investigate whether this intuition can be real since it cannot be given in our experience, it is beyond the limits of our possible knowledge. Its possibility is only a logical one: given human intuition, it is possible to think of an intuition that is its opposite; it is possible to think the negation of human intuition (as A leads to the thought of not-A). In this sense the Transcendental Aesthetic is a negative doctrine of the noumenon, which is the thought of an object that is not and cannot be given in our experience:
“Now the doctrine of sensibility is at the same time the doctrine of the noumenon in the negative sense, i.e. of things that the understanding must think without this relation to our kind of intuition, thus not merely as appearances but as things in themselves, but about which, however, it also understands that in this abstraction it cannot consider making any sense of its categories, since they have significance only in relation to the unity of intuitions in space and time, and can even determine this unity a priori, through general concepts of combination only on account of the mere ideality of space and time.” (KrV B307–308)72
So far, sensibility can only provide a necessary, although insufficient, indication of the constitution of the