An already not-so-recent trend in Kant scholarship is the shift from epistemological-methodological readings of Kant to metaphysical readings. Gava’s book is an extremely valuable addition to this literature in its bold yet carefully argued and detailed claims. But rather than constructing another metaphysical model of Kant’s transcendental idealism or emphasizing the continuity between the critical Kant and his rationalist predecessors or pre-critical philosophy, Gava structures his interpretation on Kant’s own formulation of metaphysics as a kind of science.Footnote ¹ By that, Kant means that metaphysics is a system of conceptual synthetic a priori cognitions. The Critique’s main aim, according to Gava, is to elaborate the doctrine of method of that science, an account that establishes that metaphysics is indeed a science by demonstrating its capacity for architectonic unity. This task encompasses two levels: first, showing the systematic coherence of a set of propositions and, second, showing that a single supreme principle unites all, the ‘idea’ of that science. Accordingly, Gava distinguishes between two key tasks within the Critique: 1. transcendental philosophy – enumerates the a priori concepts and principles that structure cognition, identifying their grounds in faculties of cognition and assessing their validity; 2. critique of pure reason – establishes the scope and limits of those concepts and principles so that they can form a coherent whole and achieve architectonic unity under one idea.

This guiding theme allows Gava to provide a significant contribution to Kant scholarship by drawing attention to some neglected aspects of the Critique, particularly the doctrine of method, and shedding light on the systematic nature of Kant’s project and its meta-metaphysical commitments.

Gava’s book is divided, after its introduction, into four parts. Part I clarifies the overall claim in two chapters. The first explores Kant’s distinction between the school and worldly concepts of philosophy and explains why only the latter provides unity to metaphysics. The second develops the idea that the Critique as a whole should be understood as a doctrine of method for the science of metaphysics. Part II targets the first task of transcendental philosophy in two chapters. Chapter 3 portrays the three metaphysical deductions that catalogue ‘root concepts’ for the forms of intuition, the categories of the understanding, and the ideas of reason. Chapter 4 analyses the corresponding three transcendental deductions, establishing the validity of those ‘root concepts’ in the transcendental aesthetic, analytic, and dialectic. Part III expounds the second task of a critique of pure reason. Chapter 5 explores the negative part of the project that restricts speculative reason and refutes metaphysical dogmatism. Chapter 6 shows that the B deduction includes a second element of the negative result of the critique in restricting the validity of the categories to possible experience. Chapter 7 focuses on the positive use of the ideas of reason, exploring Kant’s argument for commitment to the existence of God and the soul as forms of practical belief rather than knowledge. The last part includes two chapters that relate Kant’s project to his criticism of dogmatism (represented by Wolff) and scepticism (represented by Hume).

There are a lot of interesting and rich discussions throughout the book, but in this brief review, I will focus on one aspect that is particularly fruitful in Gava’s interpretation. In chapter 1, Gava argues that the unifying idea of metaphysics for Kant is a worldly concept rather than a school concept of philosophy. While metaphysics according to the school concept aims at organizing a priori discursive cognitions in a system, metaphysics according to the worldly concept organizes these same cognitions in relation to the essential ends of human reason, meaning ‘with the chief purpose of answering the question of whether and how the highest good is possible’ (p. 33). The primacy of the practical concept of the highest good is certainly obvious when assessing Kant’s critical project as a whole, but it is an original angle for interpreting specifically the Critique of Pure Reason, whose main concern has mostly been regarded as the possibility of synthetic a priori knowledge and the limits of human cognition. This lens allows Gava to explain seamlessly the inclusion of the regulative role of the ideas of reason in the Appendix to the dialectic and the practical belief in the existence of God and the immortality of the soul in the Canon. The regulative theoretical ideas are not leftovers from previous metaphysical systems demanding some function, and the practical postulates are not just precursors to the practical philosophy Kant envisioned but had not fully developed at the time. Rather, they belong essentially to the architectonic system of all a priori concepts, where each concept has a role assigned by the worldly idea according to the ends of human reason.

Gava’s discussion of these topics is thorough and illuminating, though I have some remarks. The ideas of reason are first mentioned in section 3 of chapter 3 regarding their metaphysical deductions. Kant offers two deductions, one from the forms of syllogism and the other from the relations in representation, and Gava notes that it is not clear why and how they yield the same results. Gava’s solution is that the derivation of the ideas is modelled on the class of cosmological ideas, which, therefore, play a ‘central role in Kant’s account of reason’ (p. 117). Unlike psychological and theological ideas, which always posit a single unconditioned condition (the soul or God), the cosmological ideas allow for both a finite first condition and an infinite regress. The cosmological ideas extend the categories of the understanding to the unconditioned and lead to antinomies. Therefore, they provide the paradigmatic examples of the dialectical illusion of reason. This is a convincing account regarding the negative critique of speculative metaphysics, but for the positive regulative role of the ideas, the opposite is true. The psychological and especially the theological ideas are more significant, as they provide the guiding principles for the systematic unity of knowledge. This coheres with Gava’s emphasis on the positive use of the ideas both for theoretical and practical reasons as a central element of Kant’s system of metaphysics, so it could be expected to come up also in the initial derivation of the ideas.

The first positive use of the ideas as regulatory for theoretical reasons is presented in section 3 of chapter 4. Gava argues that the Appendix to the Transcendental Dialectic forms a transcendental deduction of the ideas but opposes the strong readings according to which the regulative ideas are a condition for the possibility of empirical knowledge. Such readings make the systematic unity of nature constitutive of knowledge, and this transcends the limits of cognition, according to Gava.Footnote ² Instead, Gava’s weaker reading is normative. The ideas have a legitimate use because they are heuristic means for perfecting our capacity to obtain objective empirical cognitions. We can do that without ideas, but it would not be the best possible way to do it. Their indirect validity lies in their ability to facilitate the discovery of new cognitions that would otherwise remain inaccessible. While this account makes sense of the indeterminate validity of the ideas, it is not clear how the three specific transcendental ideas perfect our cognition beyond what the maxims of reason that aim at systematic unity prescribe for perfecting cognition. In this context, Gava does not make a clear distinction between the principle of systematic unity and the three transcendental ideas. Although Kant sometimes refers to the former as an idea, it is more accurate to call it a principle since it is not a representation of an object. Gava does not discuss the peculiar role of the transcendental ideas as analogues of schemata of sensibility for the principles of reason. Regarding the epistemic status of the principle of the systematicity of nature, Gava relies on the notion of ‘doctrinal belief’ from the Canon. Since the principle of systematicity is a necessary condition for meeting the epistemic end of perfecting empirical cognition, and since we do not have sufficient evidence that nature is systematic, we can only be rational if we believe, in Kant’s sense of the term, that nature is systematic. I would note, however, that this is not a belief in the sense that includes a representation of a determinate way in which nature is systematic; it is more an attitude of trust that it is rational to pursue systematization in our scientific theorizing. There are, of course, competing accounts of the regulative function of the ideas, but within Gava’s project, his account provides an interesting yet seamless link between the theoretical and practical roles of the ideas by showing that both are based on practical beliefs.

The notion of practical belief receives a thorough treatment in chapter 7. Gava interprets Kant’s argument for belief in the existence of God and immortality as stemming from the sense that it would be unfair if moral actions systematically exposed us to harm. Since the only possible grounds for a necessary connection between morality and happiness are God and immortality, we are entitled to assume their existence. Interestingly, this account suggests that Kant could focus on entitlement rather than mere hope, strengthening the justification for assuming God and immortality (p. 218). The specific details of the justification for belief are not so important for Gava’s argument about the place of the Canon within the first Critique. However, I suggest this interpretation would make the Canon quite different in being more eudaimonistic than the later versions of the argument in the second and third Critiques. First, it is not clear why, without God, we are systematically exposed to harm. There is certainly a possibility that the righteous will suffer, but it is not strictly necessary. Eudaemonists of all sorts actually argue for the opposite, that virtue leads to happiness because of the prudential benefits of moderation and social harmony. But from Kant’s perspective, even if this were true, it would be an empirical generalization without any moral significance. Already in the first Critique, Kant distinguishes moral reasons from prudential reasons.Footnote ³ Therefore, and more importantly, it is not clear how the sense of unfairness implicates our moral reasoning to justify rejecting unfairness through a strong commitment to God and immortality. Gava mentions that the problem is not that unfairness would harm moral motivation (p. 217, fn. 15). But without relying on an obligation to promote the highest good and on the ‘ought implies can’ principle, it is not clear how this commitment is stronger than a mere permissible hope based on our wish for fairness combined with the theoretical undecidability of God’s existence.

Finally, I will note Gava’s characterization of Kant’s project as ‘moderate methodological conservatism’: an approach that begins with the assumption that a priori concepts and principles are commonly used, aiming to clarify and catalogue these concepts, trace their origins, and establish their validity. This conservatism is ‘moderate’ because it is compatible with criticizing traditional metaphysics to require revising our common understanding of these concepts, for example, regarding the transcendental ideas. While the details are convincing, I wonder whether the label accurately captures Kant’s relation to the metaphysical tradition he inherited. Kant is certainly not an eliminativist or sceptic about metaphysics, but the term ‘moderate conservatism’ seems to obscure the revolutionary aspects of Kant. Even if Kant maintains the root concepts and distinctions of the tradition, it is more a case of retaining a husk and replacing the inner core. The grounding method of his metaphysics is completely novel, whether in the transcendental arguments for synthetic a priori principles or practical arguments for the ideas of reason. On the other hand, Kant is more appreciative of the tradition than Gava’s explication of ‘moderate’ suggests. Kant appropriated the tradition by uncovering its true justified meaning and diagnosing the errors that result when this aim is obscured. In this sense, Kant’s description of metaphysics as a ‘natural predisposition’ (p. 2) is more fundamental than the systematic notion that is the focus of the book. Accordingly, Leibnizian-Wolffian metaphysics is not a mere blunder of the philodox school philosophy, which proceeds dogmatically through empty pseudo-analytic propositions. There is something valuable in it because its misguided conclusions are still an expression of the legitimate ‘natural predisposition’, which is mainly practical. Gava mentions that according to Kant, ‘past philosophers failed to acknowledge the practical interest animating their theoretical efforts’ (p. 37) but emphasizes Kant’s criticism rather than the positive side of this tradition. I think that this nuanced attitude towards rationalistic metaphysics is also the connection between the three meanings of dogmatism discussed in chapter 8: dogmatism₁ as the attempt to establish metaphysical truths through conceptual analysis; dogmatism₂ as the uncritical use of synthetic a priori principles; dogmatism₃ as the affirmation of the theses of the antinomy of pure reason. The core practical interest of metaphysics is establishing dogmatism₃, mainly the freedom of the will and the necessary cause of the world. This interest leads to the illusion that dogmatism₁ can achieve positive results without assessing the validity of dogmatism₂. While in the Critique, Kant is more critical of the Wolffian tradition, in other places, the positive appropriation is salient, for example, in a 1790 letter to Kästner: ‘the efforts at criticism I have heretofore made are in no way meant (as they might appear to be) to attack the Leibniz-Wolffian philosophy. My aim is rather to pursue the same track according to a rigorous procedure and, by means of it, to reach the same goal, but only via a detour that, it appears to me, those great men seem to have regarded as superfluous: the union of theoretical and practical philosophy’ (11: 186). In the same year, Kant also concluded his controversy with Eberhard with the surprising statement that ‘the Critique of Pure Reason might well be the true apology for Leibniz’ (8: 250). Perhaps, it is a matter of taste, but I sense that the term ‘moderate conservatism’ does not do justice to Kant’s way of transforming a tradition by uncovering its hidden essence.

The above remarks do not detract from my great appreciation of Gava’s impressive project. The book offers an original reorientation to many well-trodden debates about the first Critique, carried out through a detailed yet clear reconstruction and evaluation of Kant’s arguments. This makes the book an invaluable contribution, and I highly recommend it to anyone interested in the Critique of Pure Reason.