Kant recognizes that "all our cognitionbegins with the senses, proceeds from thence to the intellectand ends with reason"¹⁷ or that "all human cognition begins with intuitions, proceedsfrom thence to conceptions, and ends with ideas"¹⁸. The a priori of the intellect versusthe experiment is similar to the a priori of the reasonversus the intellect.
The idea formed by reason about the conceptsof the intellect and, hence, about experience and phenomena, isits own pure work, which has ultimately a regulating role withrespect to the intellect. The idea of the unity of scientificknowledge is an idea of pure reason, having a regulating rolein the functioning of the human intellect, like any basic, conceptualidea in whatever field of science. Kant's view reflected no doubtan essentially real process but his regarding space and time asa priori forms of human intuition dictated this strictpurity of reason, as a sum of a priori Ideas. The Ideas as a priori concepts of reason are our theoretical modelswith respect to the concepts formed by the intellect and, finally,with respect to experience, Kant argues. But that they are generatedon a strictly pure, a priori basis is untenable. The ideaof the unity of science can only derive from a confrontation ofexperiment with reason. With Kant, reason sends some kind of conceptual,regulating waves to the intellect, and the latter does the sameto experience. This is the main way in which cognition develops,the reverse way being subordinated to the first. This cognitionmode depends on his treating space and time, as a priori.We cannot however deny that reason can form ideas by itself. Bothways are equally important.
The subtlety of Kant's insight is obviousin the distinction he makes between intellect and reason: forthe intellect functions by virtue of (formal) rules, whereasthe reason is capable of inventing, it is more creative. Reasonsets rules for the intellect. It elaborates ideas, which are illusions if about the things-in-themselves. But this property allowsreason to supplement the intellect (which synthesizes empiricaldata and orders them in a formal manner) with subtler ways andprocedures. Kant was aware that reason is fairly subtle in itswork but he rejected its dialectical subtlety. That reason buildsthe rules for the intellect is an acknowledged fact today. Variousmodern and old procedures and ways of thinking pertinent to theintellect appear, in Kant's view, as being the result of the painstakingeffort of the human reason in the course of time. The intellectworks clearly, it is like a machine, whereas the reason worksin a dim fashion until it finds a new machine-procedure for theintellect. We may righteously ask whether there will be anythingleft to be created when the whole human thinking is automated.This topic is however the object of other chapters herein. Theseparation between intellect and reason appears thus as a separation between what is formal in thinking and what establishes basicrules, principles and ideas. These properties of the human mindwere well grasped by Kant. When thinking of Kant, we image thephilosopher concerned with the powers of human reason (understoodas both intellect and reason), with man's thinking and conceptionabilities, with the powers of reason to think "purely" (which is only partially possible) with respect to man's feelingsand motivations, and with its capacity to grasp existence andthe material world by thinking.

However, Kant sets sufficiently strict limitsto reason. Everything around us and, finally, we ourselves arethings-in themselves and hence we cannot cognize ourselves. Thatis why we cannot know whether we have a (mortal or an immortal) Soul; the Soul is an Idea, a noumenon. Nor can we cognize the depths of existence, even those close to us, sincewe cannot know all these things that are near us. According toKant's view, we could not say whether they consist of atoms, andif the atoms were experimentally observed, they would still bemere phenomena, and the reason goes on similarly indefinitely. Analogously, all that we may mentally construct and prove experimentally (theoretical and experimental physics) become phenomena as ourinsight gets deeper. Unlike Kant's view, in modern science thething-in-itself is driven far off, while Kant's interpretationwould be still tenable unless we would not regard "the ultimatething-in-itself" as cognizable. What we cannot know todaycan be known in greater depth tomorrow. During Kant's time, the phenomenon could be seized as an appearance by man's senses. Nowadays,reason can be employed as a guide to experiment in order to getbeyond what used to be a phenomenon, to ever deeper phenomena.Science has proved that the thing-in-itself consists in strataof phenomena and so the phenomena reflect the thing-in-themselvesand, in a way, determine them. The thing-in-itself and the phenomenonare therefore not unrelated; the phenomenon gives us the reality of the thing-in-itself. Increasingly deeper phenomena relate onthe depth of things and of existence, and the ultimate phenomenon,which is the deepest now available, leaves behind only what wedo not yet know. Will there be a phenomenon beyond which we couldnever reach ? And, consequently, will there be an ultimate thing-in-itselfbeyond this phenomenon ? The answer is no doubt negative for we have continuously driven the frontiers of the thing-in-itselffrom body to atom, and then from atom to its constituent particlesand thenceforth farther away. We can by no means accept Kant'sview on the thing-in-itself, for then it would presuppose a limitof our reason, like a reflex in a mirror. Indeed, this limit ofour understanding must change as we pass from one stratum of phenomenato a deeper one. Science has managed to unravel Kant's thing-in-itselfbut we cannot accept that it has changed the limits of human reasonover a historical period of almost two hundred years only. Theidea of atoms was an idea of pure reason which Kant regarded essentiallyas an idea about the thing-in-itself. With Kant, atomism was oneof the elements in the antinomy of quality: "Every composite substance in the world consists of simple parts; and there isnothing that is not either simple, or composed of simple parts"(thesis), and "No composite thing in the world consists ofsimple parts; and there does not exist in the world any simplesubstance" (antithesis).

In this way, the atomism has become a phenomenonand has stepped into the sphere of cognition, unlike Kant's contention.The barriers of reason with Kant could be demolished because thethings-in-themselves were not things-in-themselves. Nevertheless,Kant understood the role of theoretical cognition and of the guiding ideas formed by the human mind. His view exhibits scientificbreadth and reflects objective truths. Indeed, few philosophieshave managed to be so impressive in construction, wealth of truthsand bright observations while starting from so peculiar a choiceon reality.
Experience and philosophical reasoning makesus aware of certain limits in our power to think and comprehend.These limits must be those of our biological "machine",that is natural limits and not artificially set as with Kant. However, if these limits are natural, then they are objective(as long as the biological "machine" goes unaltered).They may leave way for a thing-in-itself in cognition providedthat we are blind to the transparency of these limits, or, otherwisestated, provided that we seek to avoid these limits and workingwith them. A philosophical experiment allows us to employ theselimits so as to deduce fundamental properties of the objectivereality, whether guided by the current experimental (and theoretical)science or not. As shown in Fig. 1, the philosophical experimentrelies on the use of the limits or reason, as pertinent to a devicelike the brain, so as to deduce a part of the general outlineof the objective reality in its over-all profundity. Working with these limits can likewise give us cognition as results from theagreement between our being and intelligence and the objectivereality, as a natural process.

The Limit of the Thing-in-Itself14