2. Let us first see the reason forwhich Kant sought to separate human thought into Understanding (i.e. intellect) and reason and then to developthe properties and the problems of these faculties independently. It is true that Kant mentioned these faculties as a unit but onlyonce: "... the main root of human knowledge divides intotwo, one of which is reason. By reason I understand here the higherfaculty of cognition, the rational being placed in contradictionto the empirical"¹⁴.
The understanding is that part of ourthinking which comprehends phenomena, makes a synthesis of theexperimental data, builds concepts so as to generate and comprehendthe experiment, and refers to the things-in-themselves as theconcept of noumenon. However, this concept has no substance, because the thing-in-itself cannot be known: "The conceptionof noumenon is therefore merely a limitative conception, and therefore only of a negative use. But it is not an arbitraryof fictious notion, but is connected with the limitation of sensibility,without however being capable of presenting us with any positivedatum beyond this sphere"¹⁵Kant says. And later on he adds: "Our understanding attainsin this way a sort of negative extension. That is to say, it isnot limited by, but rather limits sensibility by giving the nameof noumena to things, not considered as phenomena, but as thingsin themselves. But it at the same time prescribes limits to "itself",for it confesses itself unable to cognize these by means of thecategories, and hence is compelled to cognate them merely as anunknown something"¹⁶.

But if human thinking gives substance to thenoumena, then there must be another property of thinkingwhich should have such an effect. This property is reason,which springs in Kant's first explanatory attempt as soon as spaceand time are driven away from existence and the thing-in-itself is instored. It is reason, rather than understanding which workswith the experiment, hence with phenomena, which seeks to putsomething into noumena so as to lend them substance andto turn them into reason-generated Ideas. The thing-in-itselfbecomes apparent in reason qua Idea, and both Ideaand reason become questionable, and so subject to criticism, fromthe very outset since the Idea has content about somethingwhich we cannot cognize. Another consequence is that reason is increasingly remote from the empiric, and it will only furnishtheoretical elements. Reason has a limited power to cognize. Thus,when it approaches existence in full confidence that it can cognizeit and go beyond the limits of the thing-in-itself, it can stateboth the thesis that "the world is limited in time and space"and the antithesis that "the world is infinite in time andspace". Like antinomies, as Kant calls them, provethe limits of reason and the absurdities that may be reached whenwe think that these limits can be exceeded. This shows that reasondoes not work with any experimental material, and this makes itbe so distinct from understanding, which was recognized by itsproperty to cognize what can be cognized, i.e. the phenomena.
One should now righteously ask whether reasonhas also positive properties to which one could restrict. Is theproperty of reason to form ideas only a negative property ? Byits negative properties, reason could break away from the understanding,but reason is also related to understanding since it seeks to give substance to the noumena referred to by the understanding and since it is in a relation of unity with the intellect, whichderives from the fundamental apperception, from the unity of ourbeing. This is Kant's second explanatory attempt, in which reasonis treated independently of the intellect but is neverthelessconnected to it.

This connection, by which reason is orientedto the intellect, rather than to the things-in-themselves, isresponsible for the positive properties and the role of reasonin human cognition. In a simplifying scheme, these explanationswould appear as shown below (Fig. 2).

Fig. 2

This scheme furnishes a figurative interpretationof the way in which Kant had to build something equivalentin the human mind to reflect the thing-in-itself or, otherwisestated, to reflect the abstraction of the thing-in-itself forthe phenomena. Such a reflection were impossible with thesenses and the intellect alone - the two faculties by which wecan cognize phenomena. A prolongation of the intellect by reasonwas necessary.
Reason is hence the most abstract, pure, theoreticalpart of human thinking. It is beyond the intellect, which is inrelation with the empiric, and yet it is likewise a prolongationof the intellect in terms of its abstracting properties.

The Limit of the Thing-in-Itself13