1. Schopenhauer's Encounter with Kant

In his letter to Rosenkranz Schopenhauer gives a hint for the beginning of his studies on Kant, when he writes: ‘For 27 years Kant's doctrine has never ceased to be a main subject of my studies and of my thinking’ (GBr. 166). This remark corresponds with the curriculum vitae (GBr. 52) that he attached to his application for habilitation in Berlin in 1819 and with the earliest proof of his study of Kant's works. In 1810, his second year at the University of Göttingen, Schopenhauer changed his subject of study (he had started with medicine and sciences) and began to attend lectures in philosophy, namely those of Gottlob Ernst Schulze, who had become famous for his critique of Kant laid down in a book titled Aenesidemus (Schulze Reference Schulze1969). As Schopenhauer recounts in a letter many years later, Schulze had at that time given ‘the wise suggestion to put my private effort for the moment exclusively into the study of Kant and Plato’ (GBr. 261). In 1810 he borrowed a book of Kant from the library for the first time, the Prolegomena, and the earliest note on Kant dates from this year (D XVI, 105; MR I, 12). After moving to the University of Berlin he intensified the study of Kant (but also of Schelling, Fichte, Schleiermacher, Fries and others). In 1811 we find a volume containing minor works of Kant, the Critique of Practical Reason and the second edition of the Critique of the Power of Judgement among the borrowed books. From 1811 to 1814 Schopenhauer made notebooks with commentaries on Metaphysical Foundations of Morals, Metaphysical Foundations of Jurisprudence, Logic (Jaesche), Prolegomena, Critique of Pure Reason, Critique of the Power of Judgement (third edition) and Metaphysical Foundations of Natural Science. In 1813 he borrowed the Critique of Pure Reason (second edition), and again Critique of the Power of Judgement (first edition) and Prolegomena. Later he bought the works of Kant bit by bit, but it is difficult and in many cases impossible to reconstruct the date of purchase. It is certain that he possessed the fifth edition of the Critique of Pure Reason while he was working on his main work, and marks and commentaries indicate that Critique of the Power of Judgement, Metaphysical Foundations of Natural Science, Perpetual Peace and a volume of Mixed Writings, containing Dreams of a Spirit Seer, Observations on the Feeling of the Beautiful and Sublime, De mundi sensibilis atque intelligibilis forma et principiis and Idea for a Universal History with a Cosmopolitan Purpose came early into his private library.

Schopenhauer's philosophical development until 1818 can be divided in four partially overlapping stages. (1) Up to 1812 we have the first disconnected notes reaching from the journal of 1803/4 over some poems and aphorisms to the first systematic attempts. (2) From 1812 to 1814 the manuscript remains circle around the concept of ‘better consciousness’.Footnote ⁵ (3) In 1813 the Dissertation is published. Supplemented by On Vision and Colours, appearing in 1815, this work displays all in all the mature epistemology, but the metaphysics of will is not yet founded. (4) From 1814 to 1818 the philosophical system gets its final form. During the whole period Schopenhauer's disagreements with Kant were set down in four more detailed writings: in 1812 the manuscript ‘On Kant’, in 1813 the chapter ‘Arguments against Kant's proof of the principle of sufficient reason’ in the Dissertation, in 1816 the manuscript ‘Against Kant’ and finally in 1818 the appendix to The World as Will and Presentation. Our investigation will focus on these texts, taking into account the scattered notes on Kant and the commentaries on his works.

2. Understanding and Contemplation

Even if it sounds still immature, although also a bit precocious, the earliest remaining note on Kant from 1810 already contains the core of Schopenhauer's critique of Kant. In a theatrically striking manner, he calls the critique of pure reason ‘the suicide of the understanding (that is to say in philosophy)’ (MR I, 12). Three years later the talk of suicide of the understanding is connected with Schopenhauer's project of ‘the perfected system of criticism’ which ‘will be the true and ultimate philosophy’ (MR I, 38). The note of 1810 shows the direction taken by his considerations concerning the ‘perfect criticism’ or ‘true criticism’Footnote ⁶ as they endeavoured to compensate for Kant's defects. ‘It is perhaps the best way to express Kant's defects if we say that he was not acquainted with contemplation’ (MR I, 12).Footnote ⁷ As the subsequent image explains, Schopenhauer thinks of contemplation as a kind of cognition totally different from understanding, which remains after the latter had killed itself: life is a lie, Kant (who stands for the understanding) shows that this is the case but does not know the truth, while Plato (standing for contemplation) knows it. This is the reason why Schopenhauer considers Goethe to be a necessary counterweight to Kant in his time, otherwise Kant ‘would have haunted like a nightmare many an aspiring mind and would have oppressed it under a great affliction’ (ibid.). Thus ‘true criticism’ means the completion of the human faculty of knowledge by contemplation, which is not only totally different from understanding but also degrades understanding as incapable of truth. In this connection it is important to point to the fact that Schopenhauer does not talk about the suicide of reason, but of understanding. Consequently his criticism does not refer to reason as a faculty that is ‘effusive’ in theoretical but not in practical use, as is the case in Kant. It cuts down to size the intellect as a whole without distinguishing between understanding and reason or between theoretical and practical uses. I shall return to this question in section 3.

Two years later the distinction between understanding and contemplation is modified into the distinction between abstract and intuitive knowledge. Schopenhauer compares two types of people: those who ‘usually stick to working with concepts’ and others who ‘like to represent everything through imagination (Phantasie)’.Footnote ⁸ The former way is scientific thinking and is attributed to Kant. The latter is the way of the genius whose intuitive thinking is ‘really more thorough, more exhaustive, more universal and leads to discoveries’. Scientific thinking depends on the intuitive since ‘intuitions of imagination, however, are that to which all concepts must be traced back in order to have any value’. In a comment on the Schematism chapter of Kant's Critique of Pure Reason from spring 1813, Schopenhauer explains the difference between image and concept in a way that comes very near to the definition of intuitive and abstract knowledge in the mature work. He calls an image ‘an immediate representation’ as it is ‘the reproduction of a sensual intuition’, whereas a concept is ‘the representation of a representation or an indirect representation’ (MR II, 298).Footnote ⁹ But while in the Dissertation and in the main work immediate representations are assigned to understanding and concepts to reason, here the former is a product of the imaginative faculty (Einbildungskraft), the latter the medium of understanding. And concepts can have for their content also individual things, while later they ‘are always general’ (EFR §27, 37).Footnote ¹⁰ These modifications are due to another disagreement with Kant concerning the concepts of understanding and reason (Verstand und Vernunft), which will be our subject in section 3.

In our present tracing of the project of ‘true criticism’ the comment is instructive in regard to the accusation against Kant of failing to acknowledge intuitive knowledge.Footnote ¹¹ Schopenhauer argues against Kant's concept of ‘schema’ as a mixing of both kinds of knowledge and claims that there is no difference between schema and image. And an image cannot be general, as Kant wanted to make it by using the word ‘schema’ for a kind of ‘indefinite image’.Footnote ¹² According to Schopenhauer the schema has to be replaced by a definite image (since any image is definite) that is used as a mere ‘representative (Repräsentant)’ of the corresponding concept. Its general meaning is only due to the awareness that ‘its inseparable individuality must not be considered here’ in order to have a perceptual demonstration of a general concept. Even if the interpretation of Kant's ‘schema of pure concepts of the understanding’ as an indefinite image and of the role it plays is hardly tenable, and although Schopenhauer's own theory of the representative of a concept is not yet at all developed, the comment expresses a deeper substantial difference between the two thinkers.

In Kant, the schema is ‘a product of the imagination’. However, in the case of the transcendental schema it is no image or figure, but ‘only the pure synthesis in accord with a rule of unity according to concepts in general which the category expresses’ (Kant Reference Kant1998: 274; CPR B181). The significant point is that imaginative synthesis is subjected to the unity of the category. This means, even if Kant is talking only about a ‘restriction’ of the use of understanding to the condition of sensibility (Kant Reference Kant1998: 273; CPR, B179), transcendental schematism also implies a restriction of the imaginative faculty to appropriateness to the category of understanding. If, for instance, succession in time is determined by number as the pure schema according to the category of quantity, sensuous intuition is already adjusted to subsumption under concepts, i.e. to measurability and science. Such a toppling of the imaginative faculty and subordination of intuitive under conceptual thinking is diametrically opposed to Schopenhauer's intention of claiming contemplation or intuition to be a faculty of knowledge totally different from understanding and capable of truth in the genius. When Kant concludes that transcendental schematism comes down indirectly to the unity of apperception (Kant Reference Kant1998: 276; CPR B185), Schopenhauer infers from the subordination of any representation under the synthetic unity of apperception: ‘There would be nothing but abstract concepts, but least of all a pure perception free of reflection and will, such as the beautiful, the deepest grasp of the true essence of things, i.e. the Platonic Ideas’ (WWP I, app. 522/535).

Of course the rejection of transcendental schematism had consequences for the theory of categories, which were realized immediately and published in the Dissertation. In the same comment, on the occasion of Kant's proof of the second analogy, Schopenhauer raises the question: ‘What determines the succession of those things that are in no causal connection with one another?’ (MR II, 300). Kant had written – according to the Schematism chapter – that any objective succession must be thought as necessarily determined by the category of causality (Kant Reference Kant1998: 304–5; CPR B 233–4). Schopenhauer sees this as a confusion of reason (ratio cognoscendi) and cause (ratio essendi), since he cannot accept Kant's fundamental assumption that the chronological order is already determined by the category through the schema. Thus in this connection the category of causality is not viewed by him as a condition of the possibility of experience; rather, one can experience objective succession without this category, and it is significant that Schopenhauer gives an example from the field of art.Footnote ¹³

In the Dissertation this disagreement with Kant is followed up, and we may assume that it is one of the main motives for the doctoral thesis: for in the comments on the second analogy Schopenhauer makes the point ‘that nowhere are cause, ground or reason, and motive, three very different things, sharply defined and separated’ (MR II, 300).Footnote ¹⁴ In his ‘Arguments against Kant's proof of this principle [of sufficient reason] and setting forth of a new proof written in the same spirit’, he interprets, in line with the comments, the application of the category of causality in Kant in such a way that we recognize by it the necessity of a certain kind of succession, while the reality of any objective succession is already perceived empirically (EFR §24, 28). Since objective succession is in most cases apprehended as coincidental, without cognizing the relation of cause and effect, Schopenhauer concludes that it is not procured by means of the category alone but ‘through the joint employment of the understanding and sensibility’ (EFR, §24, 24). This quotation seems incomprehensible as an objection against Kant, for the latter proposed exactly the same point. It only makes sense if the proposition ‘joint employment of the understanding and sensibility’ means something quite different in Schopenhauer than in Kant. And this is in fact the case.

In Kant's Transcendental Logic the understanding is supposed to unite the given manifold of intuition to an object by means of the categories. However, this synthesis is not the work of the understanding (which in its mere logical use is the unity of concepts and representations in judgements). Rather it is ‘the mere effect of the imagination’, whereas the transcendental function of the categories is nothing but ‘to bring this synthesis to concepts’ (Kant Reference Kant1998: 211; CPR B103), i.e. to provide the act of synthesizing with a rule by which it obtains objective validity and thus can be called ‘experience’. Therefore the understanding is defined as the ‘faculty of rules’ (Kant Reference Kant1998: 242; CPR A126). The same rules that provide the connections of concepts in judgements with logical necessity render the synthesis of the imaginative faculty necessary and thus objective. In Kant this function of categories, as pure concepts, is the only way to explain the objectivity of experience without falling back into the dogmatic assumption of objects as things-in-themselves.

Since Schopenhauer rejects the function of categories as bringing the synthesis of imagination to concepts and instead talks of ‘a necessity that is not rule-governed’ (EFR §24, 29), the cooperation of understanding and imagination as well as the definition of each must be fundamentally different from Kant's theory. And if we look at his own ‘new proof’ of the apriority of the law of causality, which rests on the supposition of an immediate ‘inference of the understanding’ that ‘does not make use of abstract concepts’ (EFR §24, 27), we have to note that the phrase ‘written in the same spirit’ can hardly be justified.Footnote ¹⁵ In Schopenhauer's proof the joint employment of the understanding and sensibility is the act of unifying time and space through the categories (which for him are not concepts). Starting with the category of causality, the understanding thus locates and creates an object of perception in space corresponding to a sensation given in time (EFR §24, 26). The whole further development leads to the well-known claim ‘that we throw eleven of the Categories out of the window and retain only that of causality, but yet see that its activity is already the condition of empirical perception, which is therefore not merely sensual, but intellectual’ (WWP I, app. 518/531).Footnote ¹⁶ In order to comprehend this radical modification of Kant's theory of the understanding and its categories we have to cross a real battlefield, where nothing of Kant's conception remained intact: the theory of the cognitive faculties.

3. Understanding, Reason, Perception (Intuition)

In his first short handwritten essay titled On Kant and dated March 1812, Schopenhauer attacks Kant's use of the terms ‘understanding (Verstand)’ and ‘reason (Vernunft)’ in two respects. On the one hand he rejects the moral meaning of practical reason. In his view the faculty that underlies morals is fundamentally different from theoretical reason. Thus to call both ‘reason’ and give the impression that there is one and the same faculty in two modifications ‘has become a source of great errors’ (MR II, 337). By theoretical reason Schopenhauer here means logic, mathematics and science but does not refer to what according to Kant makes the specific difference between reason and understanding, namely that the former as the ‘faculty of principles’ deals with the unconditioned (Kant Reference Kant1998: 387, 390ff.; CPR B356, 362ff.). With this specification, there is a connexion with the moral meaning of reason after all.

Consistently with this, on the other hand, Schopenhauer criticizes Kant's distinction between understanding and reason: ‘Who does not see that here one faculty is at work merely with more or less proficiency?’ (MR II, 337). From the understanding that ‘gives the thing an attribute’ reason differs merely in that it ‘gives it the attribute of the attribute’ (ibid.).Footnote ¹⁷ As we have already seen in section 2, Schopenhauer explains this meaning of ‘proficiency’ in his comment on Kant's Schematism by distinguishing between immediate representations and representations of representations. But there he assigns the former to imagination and the latter to understanding, which seems to be a faculty of concepts. Obviously, in 1812/13 Schopenhauer had a rather clear idea of the distinction between intuitive and abstract cognition but he was uncertain how to classify it with the terms he attempted to take from Kant. In order to get over this failing he had to carry on his critique of Kant's use of the terms. Given that for Schopenhauer there is no moral meaning of reason and at the same time that the activity of the understanding in applying categories (or later, the category of causality) does not make use of concepts, he has to define reason and understanding completely anew. As far as our investigation has proceeded, reason is already established as the faculty of concepts (representations of representations) and of theoretical judgements. The reduction to these operations means a radical degradation of reason: ‘Would reason (Vernunft) be the highest and best thing in man?! In the speculative it is the source of error … Practical reason in its perfection furnishes the ideal of the Philistine’ (MR I, 46–7 [1813]). However, the understanding is not yet sharply distinguished from reason. In a consideration regarding Kant's antinomies, included in the passage last quoted, Schopenhauer identifies ‘what Kant calls imaginative faculty’ with ‘the rest of our sensuous nature apart from the faculty of reason’ (ibid.). This remark seems to be the starting point of a process in which Schopenhauer merges Kant's productive imagination and his own idea of a non-conceptual function of categories into one faculty that he calls intellectual perception or perceptual understanding.Footnote ¹⁸ In this process a role was probably played by the fact that Schopenhauer did not know the first edition of the Critique of Pure Reason, since in the transcendental deduction of the second edition Kant himself seems to blur the difference between understanding and productive imagination when he calls the former the faculty of combining which acts ‘under the designation of a transcendental synthesis of the imagination’ (Kant Reference Kant1998: 257; CPR B153).Footnote ¹⁹

It follows from Schopenhauer's critique of schematism that he cannot accept a transcendental productive imagination, which would lead to an indefinite image. In his personal copy of the Critique of Pure Reason he notes regarding Kant's exposition of the matter: ‘imagination is used here in a way that is completely different from the common meaning of the word, thus needed an explanation if it should not be left like a hieroglyph’ (D XIII, 45). By replacing the transcendental synthesis of imagination with intellectual perception Schopenhauer upgrades perceptual or intuitive cognizance as the faculty which provides us with ‘complete representations constituting the totality of experience’ (EFR §18, 16). With his definition of reason as the faculty of abstract and discursive cognizance and understanding as the faculty of intuitive and immediate cognizance, Schopenhauer knows that he is ‘in agreement with the linguistic usage of all peoples and times’ and attacks the ‘truly confused and groundless talk about the matter’ proceeding from Kant (WWP I, app. 501/513).Footnote ²⁰

Of course, the conception of intellectual perception implies an idea of intuition (Anschauung)Footnote ²¹ that is very different from that of Kant, even if Schopenhauer refers continuously to Kant's transcendental aesthetics as ‘a work so altogether full of merit that it alone could suffice to immortalize Kant's name’ (WWP I, app. 506/518). While in Kant intuition (Anschauung) cannot give an object of experience without concepts, in Schopenhauer perception (Anschauung) ‘is immediately objective’ without concepts, and ‘empirical reality, hence experience, is already given in perception itself’ (WWP I, app. 512/525). The intuitive understanding gives ‘the whole of actual reality’ (WWP I, §4, 41/13) from which the concepts of reason are derived by ‘thinking less’ (FR §26, 147). Compared with the above quoted distinction between understanding and contemplation, where the latter was based on intuitions of imagination to which all concepts of the former had to be traced back, it is clear that within one year the understanding had taken the place of the imagination and reason the place of understanding. While Schopenhauer is quite aware of his different use of the terms ‘understanding’ and ‘reason’,Footnote ²² he seems not to recognize that in his conception Anschauung as a kind of cognizance does not mean the same as in Kant, where Anschauung means an element that constitutes cognizance. Only by taking this fact into consideration can one comprehend why Schopenhauer scolds Kant for confusing intuitive perception and concept (MR II, 463–5): what Kant claims to be ‘two stems of human cognition’ (Kant Reference Kant1998: 152; CPR B29) are in Schopenhauer two kinds of human cognition. Schopenhauer does not realize the fundamental difference between both views, when he complains about Kant's failure to explain what he means by the expression ‘that intuitive perception is given’ (MR II, 465–6; cf. WWP I, app. 496/509–10). In his eyes, Kant would have to admit a participation of intuitive understanding in the realization of a given perception, which for him is identical with the complete empirical object – ignoring Kant's famous dictum that ‘intuitions without concepts are blind’ (Kant Reference Kant1998: 193–4; CPR B75).Footnote ²³

On the other hand Schopenhauer undermines the distinction between sensibility and understanding, which is so important in Kant. The meaning of ‘joint employment of the understanding and sensibility’, which we assumed in section 2 to be fundamentally different from Kant, is now revealed as the coincidence of both in the concept of intellectual perception. Nevertheless, even in the second edition of the Fourfold Root Schopenhauer retains a distinction between cognizance of the bare possibility of succession by pure sensibility, empirical cognizance of real succession and cognizance of the necessity of succession through the understanding (EFR §24, 28; FR §23, 130). But the difference between empirical cognizance and that of the understanding has clearly been abolished, and if every real perception is intellectual it becomes questionable what the ‘pure, not empirical, perception’ (EFR 43) or merely possible perception as the correlate of pure sensibility might be. Consequently Schopenhauer writes in The World as Will and Presentation: ‘Kant called the subjective correlate of time and space, as empty forms on their own, pure sensibility, which expression, because Kant paved the way here, may be retained; however, it does not quite fit, since sensibility presupposes matter’ (WWP I, §4, 40/13).

Although Schopenhauer's critique of Kant's theory of intuition and concept must be regarded as incorrect, his critique of the underestimation of intuitive knowledge, which he mistakenly identifies with the former, is relevant if it is considered against the background of the confrontation of understanding and contemplation. As we have seen in section 2, Kant – at least in the second edition of the Critique of Pure Reason – subordinates any empirical perception to the rules expressed by the categories. Schopenhauer objects that perception or intuition is independent of concepts and that empirical reality and objectivity is the work of intuition alone, going back to images. Later the priority of intuition over conceptual thinking is condensed in the famous sentence: ‘All original thinking takes place in images’ (WWP II, ch. 7, 81/77). This is of importance for the aesthetic dimension of intuition, which at that time is not yet developed but indicated by talking about contemplation and the intuitive thinking of the genius.

The development of the aesthetic idea also starts with the comment on schematism in Kant. As a tenable interpretation of the schema, Schopenhauer had suggested calling it the ‘representative’ of a concept, but the explanation of its general meaning as expressive of the awareness that individuality must not be considered was not at all satisfying. While here the representative is only characterized as being ‘not adequate’ (MR II, 299),Footnote ²⁴ in the Dissertation Schopenhauer considers a representative of concepts that is ‘fully adequate as such’ and assumes, though yet cautiously, that it is the ‘Platonic Idea’ (EFR §40, 49). The Platonic Idea is described as a kind of ‘ideal particular (Normalanschauung)’ (ibid.).Footnote ²⁵ Schopenhauer had introduced this term in the field of mathematics, where it means ‘figures and numbers’ that are able ‘to combine the comprehensiveness of concepts with the complete determinateness of the individual representations’ (EFR §40, 45). In contrast to these figures the Platonic Ideas hold not only of the formal part but also of the material constituents of representations. In the conception of the idea as ‘an adequate representative of concepts’ (WWP I, §49, 281/276) Schopenhauer found a solution to the problem of how to explain the objectivity of empirical reality after having rejected Kant's definition of the schema. That he replaced the Kantian schema by the idea is obvious from the fact that in his comments on the New Critique of Reason of Jacob Friedrich Fries he deals with ‘normal ideas (Normalideen)’ in connection with the schema (MR II, 419). The expression ‘normal idea’ on the other hand leads back to Kant's Critique of the Power of Judgement. Schopenhauer noted in his commentary: ‘Origin of the normal idea for the species’ (MR II, 319).Footnote ²⁶

With his conception of the idea as a general intuition (which doubtlessly was influenced by SchellingFootnote ²⁷) Schopenhauer found a way to explain the general validity and thus objectivity of experience without either referring to concepts like Kant or falling back to a pre-Kantian assumption of things-in-themselves.Footnote ²⁸ In the mature theory ideas are not only adequate representatives of concepts but the ‘paradigms (Musterbilder)’, the ‘archetypes (Urbilder)’ or ‘original forms (Urformen) for all things’ (WWP I, §25, 170/154; §38, 214/202). Objectivity is primarily constituted by the aesthetic intuition of the eternal ideas, which are spread into a multiplicity of appearances in time and space as forms of sensibility that coincide with the understanding in the intellectual perception of empirical objects. Having developed the metaphysics of will, Schopenhauer calls the first mode of objectivity ‘immediate’ or ‘adequate objectivization (Objektität)’, the second one the ‘indirect objectification (Objektivation)’ of the will (WWP I, §32, 218/206). In the third instance concepts are then derived from empirical perception by abstraction.Footnote ²⁹ Since the idea as well as the empirical representation is an intuition (perception), but the aesthetic contemplation is adequate while the empirical perception is inadequate because it is restricted to the relationship to the subjective will (WWP I, §36, 238/228ff.), one could say, reversing Kant's quoted statement, that in Schopenhauer the imaginative faculty “under the designation of the understanding” acts in a way restricted to the forms of time and space by the service of will. The idea as adequate objectivization of will leads to the thing-in-itself, which shall be our final consideration.

4. Thing-in-itself

The point of one of the most quoted sentences in Schopenhauer's ‘Critique of Kantian Philosophy’ is also emphasized by himself: ‘Kant's greatest achievement is his distinction between phenomenon and thing in itself’ (WWP I, app. 482/494).Footnote ³⁰ However, it is remarkable that in his initial debates with Kant the references to the thing-in-itself are always polemical and that the term does not play any role in his philosophical considerations until 1814.Footnote ³¹ For instance, in the comment on Kant's Prolegomena he speaks of ‘the thing-in-itself, the weak side of Kant's teaching’ and notes: ‘Surreptitious introduction of the thing-in-itself through a tacit hypothetical inference of a cause’ (MR II, 290–1, 292–3). The reason why Schopenhauer rejects the thing-in-itself in the beginning is connected with the disagreements about the significance of intuitive knowledge discussed in the previous sections. In the handwritten essay ‘Against Kant’ of 1816 this connection is expressed very clearly. Since Schopenhauer means by ‘intuitive perception (Anschauung)’ the empirical cognizance that he contrasts with abstractive cognizance, and altogether ignores the fact that Kant talks of intuition and (pure) concept as constitutive elements of empirical cognizance, he wonders what Kant might understand by ‘an object of experience which is thought and is different from the intuitive representation as well as from the abstract concept’, or by an object of knowledge ‘that is supposed to be both’, hence ‘an absurdity (Unding)’ (MR II, 463–4).Footnote ³² Schopenhauer has a suspicion that this object influenced Kant's theory of the thing-in-itself. It is ‘not the thing-in-itself, although akin to it. It is an object-in-itself, i.e. an object without subject, an absurdity’, since every object ‘is either intuitive perception or concept’ (MR II, 468). In his discussion of Kant's third antinomy he explains the influence of the idea of an object-in-itself on the mistaken derivation of the thing-in-itself by the application of the category of causality beyond all phenomena (which Kant himself disapproved of and which was criticized by Schopenhauer's teacher Schulze). Thus Kant had ‘not simply set up, as he should, the object as conditioned by the subject, but only the object's mode and manner through the cognitive forms of the subject’ (MR II, 485). The remaining object in itself is then revealed as thing-in-itself by inference from the a posteriori given sensation, overlooking that ‘the whole of being-object already belongs to the forms of the phenomenon’ (MR II, 486).

Schopenhauer himself claims to have found the thing-in-itself neither in roundabout ways nor by surreptitious disclosure, ‘but we have demonstrated it directly and have recognized it where it is directly given, namely in our own will, which reveals itself to everyone as the in-itself of his own phenomenal appearance’ (ibid.). The discovery of the will as thing-in-itself in 1814 did not start from Kant's conception of the thing-in-itself but from his theory of the intelligible character. Accordingly Schopenhauer's attitude towards this theory is much more consistent than towards the conception of the thing-in-itself: ‘What Kant says, while solving the third antinomy, about the relation of the thing-in-itself to the phenomenon and of the intelligible character to the empirical, is one of the most admirable things ever said by man’ (MR II, 487). In the Dissertation Schopenhauer had found an approach to ‘man's inner essence’ by interpreting the empirical character of a human being on the basis of the assumption of a ‘permanent state of the subject of willing’ which he called with Kant ‘intelligible character’ (EFR §46, 56).Footnote ³³ At that time he had not talked about a thing-in-itself, but the idea of a subjective condition beyond time and space led him bit by bit to identify the intelligible character with the thing-in-itself.Footnote ³⁴ The intelligible character displays the features both of the thing-in-itself and the Platonic Idea. On the one side it is beyond time and space, it is no object but that which becomes objectified in actions of the body. From this point of view it has only negative predicates: it is all which the phenomenon is not, namely the thing-in-itself. On the other side it has a particular nature which becomes visible in the homogeneous form of actions. Thus it is a completely determined timeless individual idea which is spread into a manifold of actions. A year after the publication of the Dissertation, Schopenhauer conjoins the Kantian thing-in-itself and the Platonic Idea and is enthusiastic about the prospects that open up: ‘The identity of these two great and puzzling doctrines is an infinitely fruitful thought which is to become a mainstay of my philosophy’ (MR I, 143). It is needless to add that, through this fusion in the process of objectification or appearance of the will as thing-in-itself, both the Kantian thing-in-itself and the Platonic Idea lose their original meanings. In ‘Against Kant’, Schopenhauer recapitulates his deviation from Kant by describing what the latter should have done, starting from the empirical and the intelligible character in order to find the only consistent path to the thing-in-itself: