No other ens has autonomous existence, and the Ego is the only one that posits itself, and posits everything else.
The publication of the Critique of Pure Reason (1781) ‒ presented in the article that appeared in the last issue of this magazine ‒  did not provoke the hoped-for debate amongst academics. We have to wait until 1786-7 to find the first public response to Kant’s work, namely the Letters on the Kantian Philosophy [Briefe über die Kantische Philosophie] written by the former Jesuit Karl Leonhard Reinhold (1757-1823). As the first interpreter of the Critique, Reinhold considered it to be incomplete, and therefore, undertook the task of completing it. As the reader may recall, the focal point of Kant’s system of gnoseology was the intranscendibility of the I-think, which nevertheless had the ability to form representations of the thing-in-itself (tangible entia in re); however, the problem of relationship between this noumenon and the subject’s perception remained unresolved.
According to Reinhold, it is necessary to establish a causal connection between the two: the thing-in-itself is the cause of the representation that the subject can make of it. If this solution seems to clarify the point in some way, other contemporary interpreters do not agree at all. Among them was Friedrich Heinrich Jacobi (1743-1819), known for his defence of religion and faith in opposition to the prevailing rationalism of his time. Jacobi was convinced that faith and reason were irreconcilable, and since the latter inevitably led to nihilism ‒ because it founded knowledge and understanding of the world on the principle of sufficient reason, which reduced everything to a mechanical concatenation with neither origin nor purpose ‒ he believed it was better to take the «mortal leap» and seek faith in a God who is the creator and legislator of the universe. Naturally, this position also led him to confront the Kantian system, which was by then a point of reference for the German philosophy of the time, and in 1789 he published David Hume on Faith, or Idealism and Realism: a Dialogue [David Hume über den Glauben, oder Idealismus und Realismus] in which he launched a devastating attack. Jacobi considers Kant’s claim to know the world objectively to be purely illusory. In fact, he argues, first Kant reduced everything to a mere phenomenon, i.e. to a representation created by the subject for the subject, pure idealism; then, to save realism, he postulated the thing-in-itself, which would guarantee the real existence of the entia whose representations the I think produce in itself. But no causal connection can be established between the I think and the thing-in-itself (as Reinhold claimed), because causality is a category that belongs to Reason and, therefore, can only be applied to representations. Hence, the existence of the thing-in-itself is indemonstrable.
In his sceptical critique of Kantism, Gottlob Ernest Schulze (1761-1833) also proposes the same argumentation; let us explore this theme, which will prove to be fundamental in the path that leads to idealism. The thing-in-itself, based on Kant’s theory, insofar as it cannot be grasped by the complex cognitive system of the I think, is unknowable; nevertheless, the fact remains that it is at least thinkable: in fact, not only is the existence of thing-in-itself affirmed, even though it is beyond any possible knowledge, but it is also defined on the basis of its own characteristics: “thing-in-itself”, “noumenon” (from Greek νοούμενον, nooúmenon, present middle-passive of the verb νοέω, i.e. ‘that which is thought’). However, this is a contradiction in terms, because in this way you’d affirm that: “I know something is thinkable that cannot be subjected to the cognitive system of the subject”, or “I know that general nature possesses of something which, by definition, cannot be known”; therefore, the thing-in-itself is both knowable and unknowable, thinkable and unthinkable. The proto-idealistic thought of the philosopher from Rammenau, which we will now analyse, is precisely based on these problems.
Johann Gottlieb Fichte (1762-1814) believed that the thing-in-itself is not only a contradiction in terms, but an unjustifiable dogmatic residue that contrasts with the essentially revolutionary approach of Kant’s criticism. Therefore, in his view, a decisive adjustment is necessary: representational activity is entirely core to the subject that is why the existence of the external world can only be deduced from an analysis of what is present in the subject itself ‒ not grasped directly from outside, let alone postulated. In this way, the gnoseological problem must also be reformulated: one must not ask how one comes to know external objects, but rather how the subject produces its own representations. The subject is essentially an activity that produces representations, and the I-am is at the origin of all thinking and representing. One might say that Descartes’ well-known maxim is thus overturned, from ‘cogito, ergo sum‘ (I think, therefore I am) to ‘sum, ergo cogito‘ (I am, therefore I think).
The work in which Fichte presents these reflections for the first time is entitled Foundations of the Entire Doctrine of Science [Grundlage der gesammten Wissenschaftslehre] (1794), in which, in contrast to the classical approach, the idea that philosophy must ground logic and establish its principles appears, which can only be derived from the most original and fundamental operational acts of consciousness. In this way logic and metaphysics are unified, because these principles concern both the formal structure of consciousness and the possible contents of knowledge. But what are these principles, and how are they derived analytically from the I-am?
First principle: The Absolute Ego.
In classical logic, the first principle that has absolute value is the identity one, or more precisely of self-identity: A = A. For Fichte, however, this principle, far from being the original, conceals within itself an implicit postulate that remains unfounded. In saying that A is in identity with A, one must assume that A is given, or rather is posited, otherwise the principle remains a purely hypothetical theorisation. What is worse, it does not guarantee that the conclusions we draw are true at all, at least in the sense of correctly describing the world. One should, therefore, modify the formula in this way: if A, then A = A; which would mean: if A is posited, then A, once posited, is identical with itself. The question is: how is A posited? Since the activity of positing representations belongs to the I-am, then it is the I-am that must posit A. However, one could also present a judgement such as the following: “a Blibbering Humdinger is a Blibbering Humdinger”; the problem is that in reality (in re) there are no ‘Blibbering Humdingers’ (except in the minds of Luna and Xenophilius Lovegood), so this judgement is empty of content. There is only one judgement that is never hypothetical or empty: Ego = Ego. In fact, the being-posited of the Ego is the Ego. The being posited by the Ego is not a consequence, but is the sine qua non of every representation, of logic and thought itself: no other ens has autonomous existence, and the Ego is the only one that posits itself, and posits everything else.  In this sense, the principle of identity in the formula “Ego is Ego” applies unconditionally, absolutely, and indeed expresses the pure activity of the Ego. At the basis of all human activity and all knowledge is the self-consciousness of the Ego, the principle by which the Ego posits itself. Here we are, based on the Fichtian system, in the field of Reason.
Second principle: The Non-Ego.
The second principle of classical logic is that of non-contradiction, which is summarised by Fichte in the formula: «the negation of A is not equal to A» (‒A is not A). Simplifying the reasoning, one could say that ‒A is in opposition to A, but the act of opposing cannot be deduced by argumentation from pure posing. The very position of A necessarily implies the act of opposing, because in its positing A determines itself, and determination is the opposition between something that is posited and everything else that is not posited. In this sense, the principle A=A immediately implies that A is different from everything that is not A, and thus from ‒A. Obviously viceversa is also true, i.e. the position of ‒A implies that A is also posited, since in order to deny A I must first posit that same A I intend to deny. Substituting the Ego for A, it turns out that the Ego itself, by positing itself, also posits the Non-Ego as that which is opposed to it, and therefore the acts of positing and opposing are precisely both activities of the Ego.  Therefore, the principle of non-contradiction derives analytically from the activity of the Ego, which posits itself and immediately posits its own opposite, namely, the Non-Ego. The field here is naturally that of the Intellect.
Third principle: The Empirical Ego.
A thorny dilemma now arises: when the Ego posits the Non-Ego, are the two co-present or do they annihilate each other out? At first glance it would seem sensible to answer that the two dp annhilite each other, for if the position of A immediately implies the position of ‒A, i.e. its negation, then what remains is exactly nothing (if I create a vase and in the very act of creating it I destroy it, the vase is not there). And yet, in this case, since we are talking about the Ego, if this were true, it would not even be possible to ask this question: if the Ego in posing itself at the same time denied itself, there would be no Ego, hence consciousness, thought ‒ nor world. Position and opposition must therefore coexist, i.e. in order for there to be opposition between the Ego and the Non-Ego, since both are posited by the Ego, the unity of consciousness must be maintained. Fichte’s reasoning is very complex and subtle and cannot be explained in full here; suffice it to say that in the act of positing the Non-Ego, the Ego must remain self-conscious, must pose as that Ego which is positing the Non-Ego. The opposition, therefore, can never concern the absolute (total) Ego and the absolute Non-Ego, but only parts of them. In this sense it is necessary for both to be divisible, so that the Ego always opposes only a part of itself to the corresponding part of Non-Ego, while it continues to posit its entire self. In other words, the two principles limit each other, and constitute always and only a partial mutual negation. There is no subjectivity totally opposed to the world, but only a finite, limited subjectivity, which enters into contact from time to time with an equally limited and finite part of the world.  There are, therefore, different ‘dimensions’ of the Ego and the Non-Ego. To simplify, consider this small schematic:
Absolute Ego: the condition of possibility of all knowledge;
Empirical Ego: the knowing subject, i.e. a real entity;
Divisible Ego: humanity, which is divided into units of individuals;
Divisible non-Ego: nature understood as a set of distinct bodies.
The empirical Ego, being a knowing subject, knows the Non-Ego, i.e. the entities of the world, thanks to the continuous and constant connection of reciprocal limitation that exists between the latter and the absolute Ego. This relationship is dialectical in nature, which for Fichte means «synthesis of opposites by means of mutual determination». In positing the Non-Ego, the Ego triggers a tension aimed at the reconstitution of unity (the Ego, as the one who posits, would like to also assimilate what it has posited as its opposite into itself), and it attempts the feat through the cognitive act, which in some way allows it to reappropriate the Non-Ego that stands before it as ‘object’. However, since the knowing subject is that finite and limited empirical Ego, its work of knowledge is never total and simultaneous but always partial and deferred in time. According to Fichte, this eternal cognitive tension is the desire for Freedom.
In conclusion, it is worth mentioning two facts: first, for the first time we encounter a dialectic that is composed of three elements (whereas classically it had always been dichotomous), and second, the thing itself is abandoned altogether as no longer necessary to constitute a gnoseology. Realism is set aside in favour of speculative idealism ‒ where reality is nothing else but the product of dialectic triggered by the Ego’s positing itself, or its self-consciousness. A new period for philosophy begins, one that would be marked by the impressive work of the Stuttgart philosopher, G. W. F. Hegel.
 K. L. Reinhold, Letters on the Kantian Philosophy, edited by Karl Ameriks, translated by James Hebbler, Cambridge University Press, New York 2005.
 F. H. Jacobi, David Hume über den Glauben oder Idealismus und Realismus, B. Sassen (trans.), in Kant’s Early Critics, The Empiricist Critique of Theoretical Philosophy, pp. 169–175. Cambridge University Press, Cambridge 2000.
 «The posting of the Ego itself is, therefore, the pure activity of the Ego. The Ego posits itself; and the Ego is by virtue of this mere self-positing. Again, vice versa: The Ego is and posits its being, by virtue of its mere being. It is both the acting and the product of the act; the active and the result of the activity; deed and act in one; and hence the I-am is expressive of a deed-act; and of the only possible deed-act, as our science of knowledge must show.» J. G. Fichte, The Science of Knowledge, translated from german by A. E. Kroeger, Preface by William T. Harris, Trübner & Co., Ludgate Hill, London 1889, pp. 68-69.
 «Hence, that form of acting, the oppositing, is posited absolutely, and with no attached condition. ‒A is posited as such simply because it is posited.
Hence, as sure as the proposition ‒A not = A occurs among the facts of empirical consciousness, there occurs among the acts of the Ego an oppositing; and this oppositing, as far as its form is concerned, is absolutely and unconditionally possible, and is an acting which has no higher ground.» J. G. Fichte, The Science of Knowledge, op. cit. p. 75.
 «The Ego is to be = Ego, and yet it is also to be opposed to itself. But it is self-equal in regard to consciousness; and in this consciousness the absolute Ego is posited as indivisible, and the Ego, to which the
Non-Ego is opposed, as divisible. Hence, in the unity of consciousness, all the opposites are united; for in it even the Ego, in so far as a Non-Ego is opposed to it, is opposed to the absolute Ego; and this is, as it were, the test that the established conception of divisibility was the correct one.» J. G. Fichte, The Science of Knowledge, op. cit. p. 84.