This statement is fairly contradictory. Indeed,to recognize that apperception is originally empiricalwhile contending that it is equally a priori (pure) - asa prime pure cognition, independent of the conditions of sensibleintuition- is unacceptable. Kant was forced to arrive at thiscontradiction by his breaking the empirical from the pure rational,and this separation was itself dictated by his view of space andtime as being apart from objective existence. Whereas it is possible,at least conceptually, to separate the empirical from the apriori rational over a fairly large space, to split in apperceptionthe a priori rational and the empirical, placing the apriori qua a priori before is untenable. Kant's whole systemseems to stumble largely against apperception itself, against self-consciousness. In the philosophical experiment of self-consciousness*, the experiment is preceding. So, inapperception or in self-consciousness, the experiment comes first,a fact of which Kant was no doubt aware as he referred to it asprime empirical apperception. Then the rational is immediatelyattached to this experiment in an initial fusion, which appearsto be a philosophical experiment. However, by separating reasonfrom experiment and assigning unjustified, groundless priority to reason, Kant reaches the conclusion that "the empiricalconsciousness ... is subject to a pure self-consciousness apriori ... "10,which is tantamount to saying that the empirical in consciousnessis no longer prime. We can understand the inversion made by Kantbut this is doubtful. Indeed, we can accept the priority of theoryover experiment as a mode of thinking but in the case of self-consciousnessit is untenable. The treatment of apperception makes a huge breachin Kant's system. Because of this inconsistency, space and timeare ruled out as a priori forms and so the thing-in-itselfis also cast away, leading to the collapse of Kant's whole system.The result may be noticed in the succession of Kant's ideas, asshown in Fig.1, which indicates also the way in which the outsetof his theory is invalidated.

While noting this inconsistency, we must recognizeKant's merit in having grasped the importance of apperceptionas a reference aspect in any philosophy of knowledge: "Thesynthetical unity of apperception is the highest principle ofall exercise of the Understanding, of all logic, and then of transcendental philosophy"**. This is both true and fundamental, though the question shouldbe re-approached in terms of modern scientific standards.
Kant extends the empiric - a priori dichotomy to the whole tract of cognition - from the senses,to the understanding and consciousness - as it is obvious from thepassage cited below: "The supreme principle of the possibilityof all intuition***in relation to sensibility was ... that all the manifold in intuitionbe subject to the formal conditions of Space and Time. The supremeprinciple of the possibility of it in relation to the Understandingis that all the manifold in it be subject to conditions of theoriginal synthetical Unity of Apperception"11. The immediate question is what 'original and synthetic' takentogether mean. 'Original' meant empirical apperception, i.e. theempirical; the synthetical and the original combined turn theoriginal into a priori. That the empirical and the apriori become undistinguishable in the "original-synthetic"is somewhat obvious, but Kant states that apperception is apriori and re-instores the dichotomy: "The transcendental****unity of apperception is called objective, and must be distinguishedfrom the subjective unity of consciousness, which is adetermination of the internal sense, by means of whichthe said manifold in intuition is given empirically to be so united. Whether I can be empirically conscious ... depends uponcircumstances, or empirical conditions"12.
Let aside the above-mentioned dichotomy, theinsight given in the last sentence of the passage cited aboveis remarkable. Indeed, an empirical consciousness is seldom attained,but it is stored as a sense-symbol and then as a sign-symbol whichis then at work (see the essay "The experiment of consciousness" herein).

Figure 1

Fig. 1

Let us now refer Kant'sview on what we understand by philosophical experiment. From theentire human reality implied by the philosophical experiment,Kant focuses only on reason. He thinks that the philosophicalexperiment is not pure thought, since it may call our sensibilityinto play. He considers that reason can necessarily become pureonly by abolishing sensibility. Indeed, our thinking may striveto confine itself to a pure reason, although sensibility willbe implicit because the truth-value of the results of reason cannotbe independent of it. We can conceive things like the infinitenumber, time or space, which do not necessarily correspond toreality. And this does not trouble our sensibility at all. AsJohn Locke13 observed, we can imagine the infinite with all contradictionsentailed by this notion.

* Self-consciousness is regarded as a specific experimental fact in chapter 7.
** Kant's transcedental philosophy is the philosophy of the principles of pure reason, of the mode of a priori cognition.
*** In Kant's view, intuition is the faculty of unmediated sense perception of a given individual object.
**** I.e. pure, a priori.

The Limit of the Thing-in-Itself12