Karin de Boer’s latest book is an ambitious work that is destined to provoke a lively debate within the Kantian community. The thesis underlying the book is simple, very clearly expressed and systematically developed throughout its eight chapters. As the title already hints, the author challenges ‘the assumption that the Critique of Pure Reason destroyed metaphysics’, as well as the idea that ‘it established a “metaphysics of experience” and eradicated any “transcendent” metaphysics’ (p. 3). The author considers it crucial to distinguish between a ‘revolution’, to be understood as Kant’s departure from the structure of Wolffian metaphysics, and a ‘reform’ which, while preserving its basic intentions, corrects this structure by limiting its unwarranted claims, setting it on the path of a true science. This approach situates de Boer within the tradition of interpreters like Pichler, Wundt, Heimsoeth and Heidegger rather than that of Strawson or Kemp Smith. Even so, de Boer’s reading remains highly original. Taking as her guiding thread Kant’s clues in the Architectonic about the characteristics of the metaphysical system for which the CPR is supposed to be the propaedeutic, and focusing her attention on the Transcendental Analytic, she describes how the system designed by Kant offers a general metaphysics (ontology) and a special metaphysics, amended in the light of critical scrutiny, but not dissimilar in content from Wolff’s metaphysics.

In chapter 1, the author surveys the post-Leibnizian context in which Kant grew up and moved, focusing on Wolff’s metaphysics. Through a selection of passages taken not only from the first Critique, but also from letters, lectures and Reflexionen, she contends that, although Wolff did not succeed in developing his metaphysics in accordance with the scientific model that he had imposed upon himself, it is nevertheless ‘Wolffian metaphysics [that] is the main subtext of Kant’s account of metaphysics in the Critique of Pure Reason’ (p. 21). The author is forthright in admitting that her presentation of Wolff’s views is not neutral, but rather oriented by her interpretation of its reception by Kant, and this is reflected in some of her methodological choices, such as disregarding Wolff’s Latin works, which nonetheless must occasionally be referred to in order to clarify the framework of the analysis (see, for instance, p. 25). On the anti-Wolffian side, de Boer considers Crusius, whose metaphysics is to be seen in an essentially theological light and as preoccupied with moral issues, but from whom Kant would draw a sort of intellectual modesty aimed at limiting the legitimate range of the action of our understanding. However, Crusius, like Wolff, does not escape the tendency to delve into empty speculations about the soul and God. Both figures are objects of Kant’s criticism insofar as each is guilty of an error which de Boer labels as ‘continuism’, namely the assumption ‘that sensibility and thought are nothing but two ways in which we can come to know things’ (p. 39).

Chapter 2 unites Wolff, Crusius and the early post-Leibnizian philosophy as the targets of Kant’s Inaugural Dissertation of 1770. Viewing this as a pivotal work, where the method of metaphysics is identified with the ‘real use’ of the understanding, de Boer takes Kant to introduce with it a standard of intellectual purity for metaphysics. The author acutely sees the importance attributed to time in the Dissertation, and takes this as a clue for central Critical doctrines, such as the schematism. It seems to me, however, that de Boer’s interest in privileging the continuity between the 1770 text and the first Critique drives her analysis of the text. Take as an example the nature of intellectualia: the author first plausibly identifies them with ‘intellectual thoughts’ (pp. 53–4, n. 24), and then must acknowledge (as many interpreters did) that at AA, 2: 396 Kant ‘seems to use intellectualia to refer to things rather than to representations’ (p. 62, n. 43).

More importantly, through the Dissertation de Boer distinguishes two strands of Kant’s critique of metaphysics. According to the first, ‘metaphysics errs if it lets sensible determinations infuse its allegedly intellectual judgments about the soul, the world, and God’ (p. 64). According to the second, ‘metaphysics also errs if it alleges that its purely intellectual judgments constitute cognitions of objects, in other words, cognition proper’ (p. 64). Although this second strand leads to the departure from the intellectualism of Wolffian metaphysics that Kant still seems to admit in 1770, the two strands together represent a kind of track between whose rails the author moves in the following chapters in order to show that, even in a changed context, ‘Kant never abandoned the idea presented in the Dissertation that metaphysics must be turned into a purely intellectual discipline’ (p. 64).

In chapter 3, de Boer begins to assemble the principal elements of her interpretation of Kant’s Critique. She tries to find some coherence between the apparently diverse uses of the term ‘transcendental’ in that text, situating Wolff’s ontology (general metaphysics) within a general classification of ‘transcendental cognition’, which is in turn articulated into ‘transcendental philosophy’ and ‘transcendental critique’. Transcendental philosophy corresponds to a ‘first-order investigation into the a priori concepts and principles constitutive of any cognition of objects’ (p. 74) and would inherit the aspirations of Wolffian ontology with the decisive difference that they must be subjected to a preliminary critique orienting the research towards knowledge rather than things. From this point of view, Kantian metaphysics would not represent an investigation into the conditions of possible experience, but would try to reformulate in non-dogmatic terms the goals of the general part of Wolffian metaphysics, namely ontology. This project cannot be completed in the Critique, which is the place for a propaedeutic investigation understood as a ‘transcendental critique’ consisting in a ‘second-order investigation into the conditions under which the use of a priori concepts and principles is warranted’ (p. 74). The task of the latter discipline is carried out in the Transcendental Logic, whose two parts, the Analytic and Dialectic, test the aforementioned conditions in the areas of general and special metaphysics respectively. The author acknowledges that the proposed reading clashes with Kant’s unrestricted use of the expression ‘transcendental philosophy’, which in some cases seems to denote the project of the Critique as a whole without it being possible to clearly distinguish between the propaedeutic function of this project and ‘the reformed first-order transcendental philosophy that is only provisionally elaborated in the Transcendental Analytic’ (p. 94).

In chapter 4, the author turns to the long-standing dilemma posed by Kant’s claim, on the one hand, of the unknowability of things in themselves and, on the other hand, his apparent designation of them as the causes of our sensible perceptions. Rejecting previous attempts to reconcile these claims, de Boer offers a reframing of ‘Kant’s remarks on the thing in itself and the related concepts [noumenon and transcendental object] in terms of … strand [2] of Kant’s critique of metaphysics’ (p. 101). Accordingly, she contends that ‘whatever is said to affect us cannot be said to be a thing in itself in the sense of a noumenon, because the latter term merely refers to our way of conceiving of something’ (p. 102). These notions are thus to be read as conceptual tools through which Kant distinguishes the way we can think, in a purely intellectual way, quasi-objects such as those of special metaphysics without however knowing them, thereby excluding the intellectual knowledge of them claimed by Wolffian metaphysics. Even so, de Boer admits that Kant’s text resists this reading in places, conceding for instance that in a number of cases Kant in fact ‘conceives of the transcendental object as ground or cause of that which appears’ (p. 119). In any case, she tries to overcome this problem by, quite interestingly, attributing to Kant ‘a minimal and agnostic version of Leibniz’s monadology’, according to which ‘outer appearances are grounded in a monad-like something = X’ (p. 124).

In chapter 5, de Boer turns to the A-edition Deduction. Her basic thesis is that the discussion of categories as a priori rules for the construction of objects of experience is embedded in a (broader but less perspicuous) consideration of categories as a priori rules for the construction of objects tout court. She argues that the positive part of the Deduction, which, against Hume, demonstrates the objective validity of pure concepts of understanding, tends to overshadow the negative (subjective) part, where through ‘dissecting’ the pure understanding Kant rejects Wolff’s pretension to indiscriminate knowledge of all objects on purely intellectual grounds: ‘notwithstanding its purity, the pure understanding is not warranted to use categories for the purpose of determining things as they are in themselves’ (pp. 156–7).

By way of exploring the ‘mixed pedigree’ of the pure understanding, de Boer considers the doctrine of the schematism in the next chapter. There, she contends that while the doctrine of schematism is only expounded in the second part of the Analytic, it must be considered as being present from the beginning if one is to understand the basis of Kant’s reformed metaphysics. Kant’s main effort would consist in showing that ‘any a priori cognition of objects rests on non-intellectual conditions’ (p. 164). This schematization does not apply to that which is not given in the form of appearances, such as the objects of Wolffian special metaphysics, which – so de Boer – Kant conceives of through ‘deschematized pure concepts’ (p. 164). This yields de Boer’s provocative thesis that in the schematism chapter Kant distinguishes between ‘pure concepts of the understanding’ and ‘categories’ by stating that the former ‘contain or presuppose transcendental schemata’, whereas the latter ‘articulate the a priori rules at hand in a purely intellectual way’ (p. 180). It is only by reaffirming the mixed pedigree of the pure understanding, through the schematizing activity of the transcendental imagination, that we can understand how the desiderata of Wolffian ontology are rejected and the synthetic a priori judgements instantiated by the principles of the pure understanding become possible.

Chapter 7 looks at the Appendix to the Transcendental Analytic, the Amphiboly of the Concepts of Reflection, with de Boer maintaining that Kant here ‘explores a more radical avenue’, since ‘every step he takes in the Appendix is intended to grasp the exact point at which Leibnizian ontology and his own reformed version of the discipline part ways’ (p. 208). This point of departure consists in Leibniz’s (and Wolff’s) unwarranted intellectualization of the ontological domain: ‘former ontology transgressed its limits by substituting difference with sameness, conflict with agreement, the outer with the inner, and the determinable with determination’ (p. 214).

The lines of enquiry developed so far find a synthesis in chapter 8 where de Boer reinterprets the famous passage of Kant’s open letter to Fichte of 1799, in which Kant claims that the Critique exhausted all of what he had to say about ‘the complete whole of pure philosophy’. She argues that this passage does not actually contradict her view that Kant still had in mind to provide a reformed system of metaphysics, which ‘would have resembled Baumgarten’s Metaphysics in terms of both structure and content’ and whose ‘main differences from the latter can be inferred from the results of the Critique’ (p. 214). Beyond the philological disputes on the legitimacy of this reading of the passage from Kant’s letter, the author’s hermeneutic effort to describe this projected system is valuable. In accordance with the Architectonic, the system starts from a macro-subdivision of the Philosophy of Pure Reason into critique and the actual system, and develops the latter up to the four disciplines that make up rational physiology, namely, the three disciplines treated in the Transcendental Dialectic plus rational physics. These four disciplines, which cover the field of a renewed special metaphysics, do not produce synthetic a priori judgements, but offer purely intellectual determinations of their respective objects in accordance with the table of categories.

De Boer has produced a stimulating book, and her position concerning Kant’s views regarding the status of metaphysics, and ontology in particular, provoke a number of questions. For instance, given that Kant’s views on metaphysics develop in the works after the first Critique, it would be instructive to consider Kant’s late essay ‘What Real Progress has Metaphysics Made since the Time of Leibniz and Wolff?’, in which many of the topics at stake in de Boer’s book are rethought in a quite radical way. However, limiting myself to the parameters of de Boer’s analysis, I wonder whether this might be a case of that dynamic often invoked by historians of philosophy, and of which Hegel and Marx have offered admirable examples, according to which a quantitative change increased to a certain tipping point generates a qualitative transformation. Something similar might occur with the step from ‘reform’ to ‘revolution’ as the author takes these two terms: could not Kant’s reform have reached such a deep level, even though it was intended to be in continuity with the Wolffian system, that it became a real revolution? As Kant’s students were astonished to see the notes crowding his personal copy of Baumgarten’s Metaphysica, so it might be the case in Kant’s own speculation that the critical observations on the metaphysics of his predecessors had become so dense that there was no longer any room for Baumgarten’s text. Of course, this is a phenomenon that only the historian’s long view can measure and the interpreter’s penetrating understanding can assess. It is, therefore, to be hoped that de Boer will further expand this fascinating enterprise.