The reception of Kant’s doctrine of postulates in Neo-Kantianism

. The Doctrine of Postulates is one of the most disputed segments in Kant’s philosophy. How could the objective reality of the immortality of the soul and the existence of God fit in an understanding of modernity that is brought up as “secular” and “rational”? Leading scholars see the Highest Good as a “theological” denial of modernity itself. The question is how this central critique emerged in the discourse. Traces in modern Kant research lead to the period around 1900, when Neo-Kantianism was claimed to be the most important philosophy dealing with Kant. Today, most philosophers regard Neo-Kantianism as a consistent set of philosophical practices that refer to one specific meaning. In fact, “Neo-Kantianism” was thrown into the discourse within the debate between Neo-Kantian authors – Friedrich Paulsen, Hans Vaihinger, Hermann Cohen – and the famous Darwinist Ernst Haeckel, who published his wide-ranging best-seller The Riddles of the Universe in 1899. Haeckel undertook a sharp critique against the Highest Good, arguing it contained occultism, and “Neo-Kantianism” promoted this owing to its Kant “obsession”. He refers to the 1888 Kant interpretation by German occultist Carl du Prel. The reaction of Neo-Kantian authors was a broad rejection of the doctrine of the postulates, which subsequently constituted the new “essence” of Neo-Kantianism. Every differing position was excluded as non-Neo-Kantian und occult. The claimed unity of Neo-Kantianism was produced in a specific historical context to reject the postulates. The “essence” of Neo-Kantianism was then defined to provide the “right” non-occult interpretation of the postulates.

for freshmen. Only two years before the turn of the century he had published another book entitled Immanuel Kant. His Life and his Teachings that quickly became another bestseller. However, the context had changed between the publications of Paulsen's books and the problem was now the rivalry of another bestseller. Just one year after Paulsen's book about Kant, another text was published that massively shaped the debates in the following years and, through the sales figures alone, defined a new "bestseller level". I am talking about the famous Darwinist Ernst Haeckel and his main text The Riddles of the Universe (Die Welträthsel). Even though Paulsen's Introduction to Philosophy appeared as a reference (Haeckel, 1899, p. 2) in The Riddles of the Universe, something else annoyed the Jena zoologist: the currently predominant Neo-Kantian philosophy, as Haeckel criticised, entered stormy waters by passing on the three Kantian postulates -the immortality of the soul, the existence of God and freedom. These "three Great Powers of Mysticism" from the second Critique are the reason why, even in a modern world that is characterised by technical progress, "unreasonable superstition" in the form of spiritistic practices was going about (Haeckel, 1899, pp. 107-108, 353). Haeckel (1899, p. 405) demanded in the following nothing less than the rejection of the complete Kantian moral philosophy, putting in its place a monistic religion that is based on the latest findings of evolutionary biology.
Already shortly after the publication a storm of outcry flared up due to this position. After all, Kant was still seen as one of the standard writers per se by many scientists and politicians around 1900 and the call "Back to Kant" even caused a stir in contemporary politics. 1 In the year 1900, Paulsen joined the ranks of this storm and published an extensive (and polemical) discussion of The Riddles of the Universe. Haeckel's interpretation was simply an expression of the fact that Haeckel neither knew nor understood the Kantian philosophy (Paulsen, 1900, p. 35). While Haeckel, as a natural scientist, was able to set important standards (ibid., p. 32), he had completely "slept through" (ibid., p. 37) the last 30 years of philosophical thinking and was suffering from mental confusion concerning the interpretation of Kant's writings (ibid., p. 54). His dualism reproach against Kant was completely unreasonable because Kant himself had been a "monist" (ibid., p. 57). Haeckel should rather have had a look into Kant's main critical writings, instead of just quoting his pre-critical texts (ibid., p. 55). Furthermore, Paulsen complains about Haeckel's verdict against Neo-Kantianism, according to which all scientists from this school of thought propagate the immortality of the soul. A "selfproclaimed school of Neo-Kantians" is not known to him, Paulsen, and the authors who are meant by Haeckel's verdict, "who might be called so here or there", just put "much less weight on the salvation from God, freedom and immortality than on the critique of dogmatic metaphysics or the new theory of experience" 2 (ibid., p. 59).
In the following, I want to put my focus on three points that appear in Paulsen's polemics: Paulsen's claim that Kant was a monist, on the one hand, obviously refers to Haeckel's aforementioned pretension to explain the world monistically, solely by having recourse to natural laws. On the other hand, Paulsen described his own philosophical concept "with the name of idealistic monism" and that of all things in the foreword of the Introduction to Philosophy, which was also known to Haeckel. Was Paulsen trying in this case to stage a compatibility of his concept with Haeckel by using the word "monism"?
This seems to be the case, since Paulsen's second frontline is directed in a striking manner especially against Haeckel's verdict against Neo-Kantianism. Haeckel's comprehension of the essence of Neo-Kantianism was simply wrong. In contrast to this, Paulsen himself gives a definition of what the "School of Neo-Kantians" are essentially characterised by, which he pretends to know and not to know: namely the "Critique of Dogmatic Metaphysics and the New Theory of Experience".
Thirdly, Paulsen's reproach needs to be pointed out, according to which Haeckel came to his wrong Kant interpretation because he, apart from his mental confusion, only knew precritical writings of Kant and had not even read them accurately.
These three points reflect a certain historical conflict situation that is tightly linked to Paulsen's Kant book around 1900. Paulsen had particularly pleaded in the same place for a decidedly metaphysical interpretation of the Kantian moral teachings. For this interpretation, Paulsen mainly refers to three writings of Kant: the Critique of Practical Reason, the Dreams of a Spirit-Seer, as well as the controversial written notes (discussed once again in the 1880's) to the Kantian lecture on Metaphysics L1 published by K.H.L. Pölitz. Paulsen's first frontline aims here at those authors who see Kant's merits, thanks to exaggerated focus on the Critique of Pure Reason, "solely in epistemology" (Paulsen, 1899, p. XI). Particularly, the first Critique occupied "the greatest distance from his [Kant's] centre" (ibid., p. XII) that especially lies in "being in love with metaphysics" (TG, AA 02: 367, tr. H.H.). In this context, Paulsen's opinion "not to [want to] count [himself] amongst the implicit followers of Kant" (Paulsen, 1899, p. X), is obviously a reinforcement of the frontline against epistemological Kantians who had departed from Kant's "centre" and whose interpretation Paulsen refuses.
In relation to the epistemological reduction of the Kantian teachings, Kant's "Kingdom of Ends" needs to be highlighted as an integral part of the moral teachings, which Paulsen (1899, pp. 326-328) reinterprets as a "Kingdom of Humanity". On the other hand, Paulsen (1899, p. 324) polemicises stridently, just like Haeckel, against the Kantian teaching of the Highest Good and the postulates that secretly introduce a eudaemonistic bogus morality and an "Indian system of reincarnation and metempsychosis" into ethics. In this context, Paulsen (1899, p. 105) refers to his second frontline in a salient manner, namely against the authors, who "want to turn [Kant] into a spiritist".
Especially in this indicated debate, the central topic seems to be the determination of the boundaries of a Neo-Kantian discourse. Definitions serve the performative distinction of a certain position that is denoted as "Neo-Kantianism" (cf. Heidenreich, 2020). Around 1900, Paulsen, as well as Haeckel, implore a unity of Neo-Kantianism and that explicitly in connection with Haeckel's rejection of the doctrine of postulates.

Paulsen's Kant book in context
It is conspicuous that Haeckel, who later showed himself surprised by Paulsen's fierce criticism (Haeckel, 1903, p. 155), makes no mention whatever of the metaphysician Paulsen in The Riddles of the Universe as an example for mystic Kant interpretations. How does Paulsen arrive at this rejection of Haeckel if he was not explicitly attacked himself? How can we describe the context of these vehement reactions? A possible trace can be found in Paulsen's definition of Neo-Kantianism as a "theory of experience".
Even though Paulsen does not give any names, Kant's Theory of Experience (Kants Theorie der Erfahrung) is generally known to be the title of the first main work of Hermann Cohen, which he had already written in 1871 and in which he undertook a comprehensive interpretation of the Critique of Pure Reason that stood under the motto: "The critique of pure reason is critique of experience" (Cohen, 1871, p. 3). This specifically means for Cohen (1871, p. 6) installing a philosophy that is oriented towards scientific methods with recourse to Kant.
Especially this claim became highly topical in the year 1899. Cohen had published a twopart review of Paulsen's Kant book, in which several striking points of criticism came up. First of all, Paulsen, because of his assertion that the entire critical project of Kant is actually metaphysics, is said to have no idea what Kant actually intends with the word "critical" (Cohen, 1899, p. 610). Furthermore, it cannot be overlooked, as Cohen (1899, p. 611) claims, that Paulsen obviously has "a weakness for Kant-writings from the 1760's". Against Paulsen's advocacy for metaphysics, Cohen (1899, p. 612) now argues: "The transcendentalphilosophy has got its systematic basis in the examination and discovery of synthetic principles of the mathematical science." Here, Cohen explicitly frames his approach, which he already marked in his main work, as an answer to Paulsen. If Paulsen therefore is adamant that the purpose of Kant's philosophy is the salvation of rational belief, he thereby denies the deepest task of philosophy altogether (Cohen, 1899, p. 625).
However, Cohen was not the only "Neo-Kantian", who raised his voice. Just within a nine-month period and only a few months before Paulsen's review of the Riddles, the founder of the Kant-Studien, Hans Vaihinger, also took up a position on Paulsen. "Lately", as Vaihinger (1900a, p. 135) remonstrates, "several attempts to sidestep the metaphysician Kant against the critic Kant" have been made iniquitously and to counterpose the negative first Critique with "a real and positive metaphysics of reason". This countermovement is especially seen by Vaihinger to be based on the budding interest of "friends of the Swedenborgian theosophy" in "Kant's lectures on metaphysics" (ibid., p. 135) which can be seen distinctly in Paulsen's Kant book. Directly and straightforwardly, Vaihinger admits that Kant had indeed adhered to metaphysical subjects in his critical period, particularly with regard to the Kingdom of Ends or the mundus intelligibilis. But what Kant had hidden "underneath thousands of involved formulations" and a "critical disguise", Paulsen now put "into broadest daylight" (ibid., p. 140). The postulates of Kant are nothing more than "thought objects" (ibid., p. 143) and "fabrication" (ibid., p. 147) and, despite occasionally contrary statements, Kant used "disconcertingly involved formulations" in most places. After all, the postulates are just "an 'as if' those ideas were real" (ibid., p. 154).
Thus, it needs to be stated at this point: two main proponents of the contemporary Kant research had criticised Paulsen's metaphysical interpretation of Kant's moral philosophy harshly even before the controversy with Haeckel. Cohen made the reproach, analogous to Paulsen's later frontline against Haeckel, that Paulsen had reached his wrong interpretation because he only cited pre-critical writings of Kant: Dreams of a Spirit-Seer, which Paulsen had already quoted in the preface of his Kant book. Cohen insisted that the character of the Kantian philosophy, however, exhausted itself in his theory of experience. Vaihinger, on the other hand, saw Paulsen's theses as an offshoot of a longer philosophical fad, namely a too strong focus of Swedenborgians on the already mentioned lecture notes, which Paulsen also referred to. The search for relevant epistemes leads to an area that has already been mentioned: the Kantian lectures.

The Kant-Swedenborg-debate and the "Lectures on Metaphysics"
The research on the notes of Kantian lectures is obviously no central topic in present-day research. Still mostly unanswered are the demands of Steve Naragon (2000) for an extensive historisation of the text of these notes and its emergence. First advances in this area were achieved with an anthology published by Bernd Dörflinger (2015). 3 The Leipzig constitutional law expert Karl Heinrich Ludwig Pölitz 4 had already published the notes referred to as L1 in 1821. Pölitz, who referred to the content of these notes as remarks of the "real Kant" (Pölitz, 1821, p. VI), intended to liberate Kant from the then circulating accusations of atheism (ibid., p. XI). In particular, the speculations of Kant about the pre-and postmortal existence of the soul and his appreciation of the Swedenborgian teachings (V-Met-L1/Pölitz, AA 28: 253-258) form the central anchor points for Pölitz.
The discourse on Swedenborg and his claim to have been in contact with spirits after a "religious crisis" due to divine compassion and to have recognised the true nature of the intelligible world (Stengel, 2011, p. 36; 5 had already been conducted in the eighteenth century. Since Kant was generally known to have dealt with Swedenborg in detail, the relationship between Kant and Swedenborg was addressed frequently. Contemporarily, the recipients disagreed in every way on how to comprehend this relationship. Authors, who recognised a great continuity between both, had a wide influence well into the nineteenth century.

Spiritism around 1900
In the 1880's the lecture notes and the question of their historical and systematic classification were again at the top of the agenda of the Kant research. In 1888 a new edition of a part of the Kantian metaphysics was published under the title Kant's Lectures on Psychology (Kants Vorlesungen über Psychologie). The publisher was the Munich philosopher and occultist Carl du Prel. Du Prel was not only the most important representative of German Spiritism (Sawicki, 2015, p. 306), but also kept up a correspondence with Vaihinger over the years (Kaiser, 2008). Du Prel now claimed in his preface that Kant appeared not only in his lectures, but also in his Critique of Practical Reason not just as an unmistakable Swedenborgian (Prel, 1964a, pp. 34, 44-45, 50), but also as a progenitor of modern spiritism (ibid., p. 57).
Vaihinger publicly commented on du Prel's text: i.a. in 1891 in a review in the "Archiv für Geschichte der Philosophie" and in 1892 in the second volume of his well-known Commentary on Kant's Critique of Pure Reason (Commentar zu Kants Kritik der reinen Vernunft). Analogously to his later critique of Paulsen, Vaihinger admitted that Kant had also been inclined towards the Swedenborgian views on the nature of the soul and the mundus intelligibilis in his critical period, but that those had only existed as private opinions. However, these private opinions had no effect on his epistemological philosophy, as Vaihinger insists. In the moral philosophy, on the other hand, these could indeed be found, albeit only as necessary fictions. Additionally, these originated merely in the Pietist upbringing in Kant's own parental home, thus Vaihinger (1891, pp. 722-723;1892, pp. 512-513) concludes.
Vaihinger's Kant-Studien played a central role in this frontline. Vaihinger (1899;1900b;1901a;1901b;1902) reinforced more and more the stance that a scientific engagement with Kant's moral philosophy could only be possible if the respective author joined the "as-ifinterpretations" of the postulates. All positions that deviate therefrom were stigmatisd by Vaihinger as disguised spiritism. Until his withdrawal from publishing in 1904 (due to an eye disease), Vaihinger possessed the discursive power to have a determining influence, as the founder of the Kant-Studien, upon the "right" and "wrong" of an interpretation, for instance of the second Critique.
And yet it was not only about points of view that designated themselves explicitly as spiritistic. Friedrich Paulsen's above-mentioned dissociations against authors, who wanted to "turn [Kant] into a spiritist", appears here as a fit occasion for Vaihinger to ascribe to Paulsen exactly this position. For, as Vaihinger (1895, p. 420) observes in another text, it was of all people du Prel who was the driving force for the reawakened interest of the Swedenborgians in those lectures, whose coming "into broadest daylight", Vaihinger believed to have perceived in Paulsen. This seems the more conspicuous as du Prel identifies in his preface Vaihinger's first volume of the Commentary (Commentar) explicitly as the source for his occupation with the metaphysical lectures (Prel, 1964b, p. 14). Vaihinger with his Commentary was indeed, alongside Benno Erdmann (1883;1884), one of the central authors in the debates around the assessment of the lectures in the 1880's. Du Prel (1882) in turn had reviewed the Commentary in the magazine "Die Gegenwart".
Paulsen and his metaphysical interpretations, which strikingly often invoke the Dreamswritings as well as the L1, appear to be the actual consequence of spiritism in Vaihinger's discourse: a Neo-Kantian author who transfigured Kant's private opinions on the immortality of the soul into his central philosophy. Therefore, the frontline against spiritism served as a procedure of exclusion against a competing Neo-Kantian interpretation within the discourse. Paulsen obviously defends himself exactly in view of this fact against Haeckel's Kant interpretation, whose mysticism reproach Paulsen feels directed against himself, following the polemics of Cohen and especially Vaihinger. "Neo-Kantianism" is herein identified with the Cohenian reading, which Paulsen dissociates himself from. At the same time, Paulsen just seems to approximate his own (i.e. in his sense non-Neo-Kantian) interpretation of Kant to Haeckel's, namely through the strategy of calling Kant a monist, whose concept of God Haeckel would also have to be able to accept. Interestingly, in 1903, Haeckel (1903 reacted to this in his epilogue to the popular edition (Volksausgabe) of the The Riddles of the Universe by explicitly quoting Hermann Cohen and Hans Vaihinger as his authorities for his interpretation of the postulates. As a consequence, Haeckel even enters himself into the discourse on Neo-Kantianism that was defined by Paulsen, in order to distance himself from Paulsen's metaphysics and at the same time to pose himself as a canonical Kant scientist.

Conclusion
Against du Prel's claim that Kant had laid the foundation for mysticism in his second Critique, but also against Paulsen, Vaihinger now declares the postulates to be fiction. In his main work The Philosophy of "As If", which was published in 1911, Vaihinger (1913, pp. X-XIII) claims that the fictionalistic Kant interpretation had been acknowledged by all Neo-Kantian authors, also by Paulsen. In the context of the debate between Paulsen, Vaihinger and Haeckel, a discursive point can be discerned, in which the unity of Neo-Kantianism appears likewise as a systematic as well as a scientific political argument (Köhnke, 1993, p. 15). It became apparent that the zoologist Ernst Haeckel was tightly connected with the debate around the "essence" of Neo-Kantianism. In the context of his harsh criticism of the Kantian doctrine of postulates, Haeckel had stylised the unity of Neo-Kantianism as polemics, in order to put the contemporary Kant research under the general suspicion of spiritism. As a result, this reproach apparently formed a central hub for the later intended extensive rejections of the doctrines of the Highest Good by Vaihinger and Hermann Cohen (1910, p. 357;1907, p. 415). The epistemological foundation of the debate formed the monopolising of Kant as a spiritist as it had been initiated by du Prel in 1888.
The systematic unity of Neo-Kantianism, acknowledged by many current researchers (Beiser, 2017, p. 1;Sieg, 1994;Krijnen, 2012, p. 69;Flach, 2012, p. 12) obviously cannot be separated from historical and scientific political questions, in whose context this unity was conjured. The debate around Kant and around the "essence" of Neo-Kantianism immediately before and after 1900 was greatly shaped by the conflict over the interpretational sovereignty of the doctrine of postulates. In particular, after the publications of Carl du Prel and Ernst Haeckel and the debate concerning Paulsen's Kant book, the doctrine of postulates was considered a segment which would form the gateway for spiritism. The rejection of the Kantian posited "objective reality" (objective Realität; KpV, AA 05: 132) of the immortality of the soul or the existence of God, apparently formed in this conflict situation the epistemes for the definition of a Neo-Kantian philosophy, which was decidedly not supposed to meet the reproach of Haeckel of being secretly spiritistic itself.