In the almost 250 years separating us from the publication of its first edition, Kant’s Critique of Pure Reason has been interpreted in several ways. Philosophers and scholars from different periods and with different backgrounds (from Heidegger to neo-Kantians, including more recent scholarly interpretations up to today) have read it as a thorough criticism of previous special metaphysics, as a general theory of knowledge or a particular theory of a priori cognitions, as the philosophical foundation of natural science (especially Newtonian physics), or as the starting point for a new metaphysics, to name just some examples. All these readings are at least partially grounded, and their plausibility shows the manifold of concerns, and thereby the theoretical richness, of Kant’s first Critique. However, none of them takes into account a further possible interpretation which is striking because this interpretation is explicitly suggested by Kant himself in the Preface to he second edition of the work. There he writes that the Critique is “not a system of the science itself” but, rather, “a treatise on the method [ein Tractat von der Methode]” (B xxii). The same qualification returns in a central section of the work, namely in the metaphysical deduction of the pure concepts of the understanding, where Kant claims that he will analyze such concepts “to the degree that is sufficient in relation to the doctrine of method [Methodenlehre] that I am working up” (A83 B109). Thus, although secondary literature has surprisingly often neglected these passages, it is Kant himself who claims that the Critique of Pure Reason must be understood as a doctrine, or a treatise, on method. However, if we take Kant’s claim seriously, several questions arise. How can the Critique be a doctrine of method, if a doctrine of method as such is supposed to elucidate the procedures of investigation concerning a specific discipline, while the Critique does so only in the Discipline of Pure Reason, and even there only partially? Speaking of the Discipline, how can the Critique as a whole be a doctrine of method, if Kant explicitly qualifies only its second part (i.e. the Transcendental Doctrine of Method) as such? Even admitting that the entire Critique is such a doctrine, which discipline does it concern? And what must it establish with regard to this discipline?

The aim of Gabriele Gava’s book is to answer precisely these questions. More particularly, Gava’s aim is to show that the Critique of Pure Reason is the doctrine of method of metaphysics, with the latter understood as the discipline encompassing valid a priori cognitions concerning objects of possible experience. Accordingly, the task of the Critique is to show that metaphysics “can be considered a science because it forms a ‘system’ with a certain unity, which Kant calls ‘architectonic’” (p. 2). Moreover, Gava attaches central importance to a remark in the Wiener Logik claiming that a doctrine of method “can come only at the end of a science, because only then am I acquainted with the nature of the science” (XXIV 795). Thus, his overall thesis is twofold: (i) the Critique of Pure Reason is the doctrine of method of metaphysics that must prove the possibility of metaphysics as a science insofar as it is capable to achieve architectonic unity, and (ii) such a doctrine comes only “at the end” of metaphysics, i.e. after metaphysical cognitions (or at least the fundamental ones) have been established.

To prove both points, Gava draws a distinction between two disciplines that, in his view, Kant presents in the Critique, namely “transcendental philosophy” and the “critique of pure reason”. On the one hand, and moving from Kant’s characterization of it as the first part of metaphysics of nature in the Architectonic of Pure Reason (A845 B873), Gava conceives of transcendental philosophy as the discipline that must first identify a priori concepts and principles for the cognitions of objects and then prove their validity. The former task is performed by metaphysical deductions, the latter by transcendental deductions (the plural is intentional, since one of Gava’s main claims is that not only the Transcendental Analytic but also the Aesthetic and the Dialectic include both a metaphysical and a transcendental deduction). On the other hand, the critique of pure reason is the discipline that, relying on the valid a priori cognitions established by transcendental philosophy in the Doctrine of Elements, must show that these cognitions and, by extension, metaphysics as the discipline including them can be a science insofar as it can achieve the specific kind of systematicity that is the architectonic unity considered in the Doctrine of Method. This clear distinction between transcendental philosophy and critique of pure reason, whose relationship has traditionally been seen as problematic or even neglected, constitutes the heart of Gava’s interpretation of the Critique of Pure Reason, and consequently permeates all the four parts of the book.

After the Introduction, in Part I (Metaphysics as a Science and the Role of the Critique of Pure Reason) Gava presents in detail his interpretation of the Critique as the doctrine of method that must establish the possibility of metaphysics as a science by showing that it can achieve architectonic unity.

Chapter 1 considers Kant’s account of architectonic unity in order to show that this particular kind of unity is different from mere systematicity. Architectonic unity certainly requires systematic coherence, which means both that (i) its cognitions are interconnected by means of logical implication, explanatory support or both, and that (ii) the unity these cognitions form does not include contradictions. However, systematic coherence is not sufficient to achieve architectonic unity because the latter must also realize the “idea” of a science, which idea both “defines the fundamental object of that science” and “prescribes the ordering of the body of cognitions that form that science” (p. 29). Thus, systematic coherence and the capacity to realize the idea of a science constitute the two “minimal criteria” of architectonic unity, which in turn constitutes the necessary but also sufficient criterion of the scientificity of metaphysics. Moreover, examining the distinction between the school and the worldly concept [Schul- and Weltbegriff] of philosophy provided in the Architectonic of Pure Reason, Gava shows that only the latter allows metaphysics to become a science. By focusing merely on the logical perfection of cognition “without having as its end anything more than the systematic unity of this knowledge”, the school concept can only provide metaphysics with a “technical unity” related to arbitrary ends. On the contrary, the worldly concept relates “all cognition to the essential ends of human reason” that are established a priori through the idea of a science, thus being able to provide metaphysics with “architectonic unity” (A838-839 B866-867).

In Chapter 2, Gava discusses his reading of the Critique of Pure Reason as the doctrine of method of metaphysics by focusing on Kant’s account of the function of a doctrine of method. Distinguishing between that of general logic and that of particular sciences, he claims that the task of the doctrine of method of a particular science is two-fold: it must (i) “provide object- or cognition-dependent methodological rules regarding how to proceed” (p. 42) in the science at issue and (ii) show that this science possesses architectonic unity. Accordingly, he shows in what sense the Transcendental Doctrine of Method and the Critique as a whole can both be considered doctrines of method of metaphysics: the Critique as a whole is such a doctrine, but this doctrine includes both transcendental philosophy and the critique of pure reason as two different disciplines performing different tasks. Thus, the Doctrine of Method carries out the critique of pure reason, which shows that metaphysics can achieve architectonic unity; as such it relies on the valid a priori cognitions established by transcendental philosophy in the Doctrine of Elements. This last consideration leads to one of the main results of Part I, namely the acknowledgment that, although it constitutes a unitary doctrine of method of metaphysics, the Critique of Pure Reason nevertheless includes transcendental philosophy and the critique of pure reason as two different disciplines, which therefore require two different methods.

In Part II (The Method of Transcendental Philosophy), Gava considers the first of these disciplines, transcendental philosophy. More precisely, he takes into account both the metaphysical and the transcendental deductions provided in the Doctrine of Elements, since they correspond to the two aims of transcendental philosophy, namely to identify fundamental concepts and principles a priori for the cognition of objects (metaphysical deduction) and to prove their validity (transcendental deduction). In this regard, one of Gava’s main theses is that each section of the Doctrine of Elements includes both a metaphysical and a transcendental deduction, since each section identifies and proves the objective validity of what he, following Kant, calls “root concepts [Stammbegriffe]” (A13 B27) for the cognition of objects. Being the fundamental a priori cognitions that make synthetic a priori claims possible, they include not only the pure concepts of the understanding but also the pure intuitions of sensibility and the ideas of pure reason.

This is the reason why Chapter 3, which is devoted to metaphysical deductions, begins by focusing on the Transcendental Aesthetic. Gava shows that the metaphysical exposition of space and time actually amounts to a metaphysical deduction, since it identifies space and time as the root concepts of sensibility and shows their original intuitive nature. His reconstruction of Kant’s argument in the Aesthetic deserves particular attention insofar as Gava succeeds in achieving two remarkable results. On the one hand, he preserves the terminological coherence of the text by arguing, against traditional readings, that Kant is not incoherent in talking about the “concepts” of space and time. Gava convincingly shows both that Kant admits conceptual representations of them and that the point of their metaphysical expositions is nevertheless that these conceptual representations are made possible by more fundamental ones, which are not conceptual but intuitive. On the other hand, Gava shows that the theoretical legitimacy of the concepts of space and time does not imply that their metaphysical expositions end up being examples of mere conceptual analysis that, as such, can only yield conceptual and therefore merely analytic knowledge. On the contrary, in virtue of an accurate reconstruction of Kant’s argument for the singularity of space and time, Gava is able to show that this argument yields genuine synthetic knowledge, since the singularity of space and time cannot be found by means of mere analysis of their concepts. After the metaphysical deduction of pure intuitions, he considers those of the pure concepts of the understanding and of the ideas of pure reason, dealing in both cases with several central issues debated by scholars. With regard to the former, he discusses topics such as the completeness of the table of the categories, the link between concepts and judgments, and the way in which concepts are brought under other concepts in judgments; moreover, he shows that Kant does not merely adopt the table of judgments from the logicians of his time and that, on the contrary, the table of judgments of general logic is not the same as that of transcendental logic. With regard to the metaphysical deduction of ideas, the main issue considered is how pure reason arrives at the idea of the unconditioned. Gava shows that in the second section (On Transcendental Ideas) of Book I of the Dialectic Kant provides two different (and contrasting) accounts for it, grounded respectively on the universality with which a property is predicated under a certain condition in the major premise of a universal categorical syllogism (B379) and on the regress through prosyllogisms in the series of premises (B386-389). This difference leads to a further difference concerning the way in which the three ideas of reason or, more precisely, their three classes are derived, namely from the three logical forms of syllogisms (B379) and from the possible relationship of a representation with the subject, with the object as an appearance, and with all things in general (B391). Focusing in particular on cosmological ideas, Gava claims that the second account is more adequate and that Kant’s inconsistency in providing two different accounts is explained by his attempt to fit psychological and theological ideas into an overall framework that is first obtained through cosmological ideas, since these play a primary role in his account of reason and the unconditioned in general. In addition to its careful textual analysis, Chapter 3 provides one of the most important results of the book by proving that, contrary to what has often been thought, Kant does not start by presupposing a distinction between different cognitive faculties, which in this case could well be seen as arbitrary. On the contrary, he distinguishes these faculties by examining the nature and function of their root concepts (intuitions, categories, ideas), and Gava’s accurate reconstruction of root concepts of sensibility, understanding, and reason clearly shows how it happens. In his words, and despite their obvious differences, all metaphysical deductions have something in common, since “they all point to the origin of root concepts for the cognition of objects, and they contribute to offering a characterization of different faculties by emphasizing what is specific to these origins” (p. 120).

Chapter 4 carries out the second task of transcendental philosophy, namely to prove the validity of the root concepts presented in Chapter 3. Accordingly, it examines the transcendental deductions Kant provides in all the three parts of the Doctrine of Elements. Starting from the Aesthetic and focusing on space, Gava collocates its transcendental deduction in its Transcendental Exposition and divides Kant’s argument into two parts, reconstructing its several steps and showing that Kant proves the objective validity of the intuition of space but not of its concept, which is easily explained by noting that the latter is “only an expression” (p. 133) of the former, on which it is grounded. In the Analytic and the Dialectic Gava follows the same pattern, thus identifying the sections that include the transcendental deductions and dividing them into clearly separated steps. In the Analytic, he focuses on the B-version of the deduction, which he claims is preferable in virtue of its clarity, and divides it into two parts (found at §20/B143 and §26/B160-161), reconstructing their several steps. His main point is that the two parts of the deduction prove different theses, and that the first must be completed by the second. More particularly, the first part proves that the categories are necessary for giving any unity to a manifold of intuitions, which manifold can be either empirical or pure; in this way, the first step establishes that the categories are objectively valid. However, it does not establish how they are objectively valid: indeed, by abstracting from the pure forms of intuition, the first part leaves open the possibility that the categories can provide unity to an empirical manifold without a corresponding synthesis of a pure manifold. Only the second part of the deduction proves that the categorial synthesis of an empirical manifold must always be accompanied by a categorial synthesis of a pure one, thereby explaining how the categories can have objective validity, i.e. can provide a priori cognitions concerning objects of possible experience. Finally, in the Dialectic Gava focuses on the meaning of objective validity with regard to ideas. Identifying their transcendental deduction in a specific paragraph of the Appendix (B698-699), he reconstructs the steps of Kant’s argument, showing not only that the function of ideas as heuristic tools for empirical knowledge is sufficient to affirm their (indirect) objective validity but also that they can be taken transcendentally as referring to existing objects, but only in the sense that our “belief [Glaube]” in them is rationally justified. Chapter 4 ends with the acknowledgment that, since they are carried out in different ways and concern different a priori cognitions, the three transcendental deductions do not share the same structure; but they share the same aim, namely to prove the validity of the root concepts of pure sensibility, pure understanding, and pure reason, as requested by the second task of transcendental philosophy.

Relying on the results established in Part II, Part III (The Method of the Critique of Pure Reason) is devoted to the second discipline Kant carries out, the critique of pure reason, which must prove the possibility of metaphysics as a science by proving that it can achieve architectonic unity. Gava claims that the critique of pure reason includes both a positive and a negative task. The former consists in limiting the validity of the root concepts for the cognition of objects established by transcendental philosophy, the latter in showing that metaphysics can achieve architectonic unity.

The negative task of the critique, and the way in which it is carried out, is considered in Chapters 5 and 6. In this regard, Gava’s main thesis is that each part of the Doctrine of Elements includes a limitation of the validity of the root concepts established by transcendental philosophy in that part. Accordingly, the Aesthetic includes not only the identification and proof of the validity of the pure intuitions of space and time (transcendental philosophy) but also their limitation to the domain of appearances and the consequent negation of their validity with regard to things in themselves (critique of pure reason). Gava shows this by means of a clear reconstruction that, moreover, explains the relationship between Kant’s argument and the sections of the metaphysical and transcendental expositions of space (and time) upon which it rests. In the Analytic, the limitation of the objective validity of the categories appears within the B-deduction, which therefore includes both the positive argument of transcendental philosophy and the negative one of the critique of pure reason. Focusing on §§22-23 and connecting it to important remarks of the Metaphysical Principles of Natural Science (1786), Gava reconstructs the negative argument and shows how it rests on the first step of the transcendental deduction, thereby showing not only that the limitation of the validity of the categories is already contained in the deduction that proves it but also that there is a clear continuity between the negative argument concerning pure intuitions and that concerning the categories. Finally, in the section concerning the Dialectic Gava pays special attention to the cosmological ideas and the transcendental principle of reason affirming the existence of the unconditioned for a given conditioned in order to show that ideas are not fit for cognition of objects and, therefore, that the (indirect) objective validity transcendental philosophy Kant attaches to them is limited.

The positive task of the critique of pure reason is considered in Chapter 7. Here Gava aims to show that metaphysics can achieve architectonic unity without overstepping the limits of the validity of root concepts established by the negative side of the critique. More specifically, since God and the soul are an essential part of metaphysics and therefore are required by the “idea” of this science, the positive side of the critique of pure reason must provide an adequate account of their systematic place within Kant’s metaphysics. To show how the critique carries out this positive task, Gava takes into account the Doctrine of Method and especially the Canon of Pure Reason. Here he does not limit his reconstruction to the long-acknowledged theoretical undecidability of freedom, immortality, and God; rather, he provides a detailed analysis concerning, on the one hand, Kant’s practical arguments in support of God’s existence and the immortality of the soul and, on the other, his account of belief. Accordingly, Gava shows the three results through which the possibility of the architectonic unity of metaphysics (and therefore its scientificity) is established: (i) Kant establishes the theoretical undecidability of God and immortality as objects of pure reason, thereby putting an end to the conflicts that have prevented metaphysics from achieving systematic coherence; (ii) he provides practical arguments supporting a grounded commitment to God and immortality, which allows to include them within metaphysics as the idea of this science requires; (iii) Kant provides an account of belief as a form of “taking-to-be-true [Fürwahrhalten]” able to show that the commitment to God and immortality motivated by his practical arguments is not grounded on “objective grounds” and therefore does not provide actual theoretical cognitions about God and the soul, which would have contradicted not only Kant’s critique of rational psychology and theology but also the limitations of the objective validity of ideas established by the negative side of the critique. Thus, by showing that Kant’s account of God and the soul not only avoids the contradictions that have prevented metaphysics from achieving systematic coherence but also provides these two ideas with a systematic place within metaphysics in virtue of practical arguments explained by Kant’s account of belief, the positive side of the critique of pure reason shows that metaphysics can achieve architectonic unity, thereby establishing its possibility as a science.

In the last part of the book, Part IV (Kant on Dogmatism and Scepticism), Gava focuses on Kant’s interpretation of Wolff and Hume and of how his own project in the Critique relates to (Wolffian) dogmatism and (Humean) scepticism, which Kant conceived as the paradigmatic representatives of the two other possible approaches to metaphysics in addition to transcendental idealism.

Chapter8dealswithWolff.Gavaprovidesaninterestingdistinctionbetweenthreedifferentcharacterizations of dogmatism, which conceive of it respectively as (i) the pursuit of demonstrations from concepts alone, (ii) the absence of critique and the unwarranted use of synthetic a priori principles, and (iii) the affirmations of the theses in the Antinomy of Pure Reason. Through a subtle analysis of these three meanings of dogmatism and their mutual relationships, he shows that Kant relates his own account of the “dogmatic procedure” of reason to a preliminary inquiry into the validity and limits of certain synthetic a priori principles, which conception is compatible with the previous distinction between transcendental philosophy and critique of pure reason.

Chapter 9 deals with Hume. It starts from two issues that have divided scholars, namely Kant’s interpretation of Hume’s doubt about causality and his interpretation of the affinity of Hume’s philosophical project with his own. Gava aims to show that apparently contrasting readings of Kant’s interpretation of Hume can be reconciled through his distinction between transcendental philosophy and critique of pure reason. In order to do this, he again distinguishes between three possible readings of Hume’s scepticism about causality, respectively representing challenges (i) to natural science and ordinary knowledge, (ii) to general metaphysics, and (iii) to special metaphysics. Rejecting the first reading, Gava shows that the second and the third are compatible because they represent Kant’s interpretation of Hume from the standpoint of transcendental philosophy and of the critique of pure reason, respectively. Thus, Kant’s account of Hume is two-fold: on the one hand, Hume is an antagonist of Kant’s project insofar as he puts into question the possibility of synthetic a priori judgments in general metaphysics (transcendental philosophy); on the other, he is a “fellow traveler” (p. 266) insofar as he wants to stop controversies in special metaphysics (critique of pure reason). These considerations, followed by a brief conclusion, close Part IV and, with it, the volume.

Gava’s book is excellent. Taking seriously Kant’s central yet often neglected claim that the Critique of Pure Reason is a treatise on method allows him to reaffirm its primarily methodological nature and to interpret systematically its several sections and topics as belonging to the unitary fundamental issue of method, thereby filling a significant gap in secondary literature. Moreover, Gava’s achievements concern not only Kant’s views on method but also his meta-philosophy and, more precisely, his meta-metaphysics. As Gava convincingly shows, the first Critique is a doctrine of method specifically devoted to metaphysics, which means that Kant’s inquiry on the method of metaphysics is at the same time an inquiry into its fundamental cognitions, its aim, and, most importantly, its possibility to become a science, which are all meta-metaphysical topics. Thus, the acknowledgment and valorization of Kant’s methodological and meta-metaphysical concerns is undoubtedly one of the main merits of the book. But it is not the only one. A second merit is the rigorous analytic approach to the text that Gava displays especially in Parts II and III, which allows him to reconstruct accurately not only the structure but also the single steps of notoriously difficult sections of the Critique such as the metaphysical and transcendental deductions. The exposition of interesting aspects of the book could continue, including for example the characterization of Kant’s approach to metaphysics in terms of “methodological” and “common sense conservativism” (pp. 66-69) or Gava’s choice to present his theses in a continuous comparison to those of other authoritative scholars. However, let me conclude by briefly returning to the heart of his interpretation of the Critique, namely his distinction between transcendental philosophy and critique of pure reason. As the entire book shows, this distinction is a powerful interpretative tool that, far from applying only to specific sections of the Critique and not to others, allows Gava to provide a comprehensive reading of the Critique of Pure Reason as a whole, which is an impressive result. Understanding the Critique as including two different disciplines with different aims allows one to appreciate the complexity but also the richness of Kant’s inquiry by showing that it keeps together both the proof and the limitation of the validity of the fundamental a priori cognitions of our pure faculties. Moreover, conceiving these two disciplines as different parts of a unitary doctrine of method of metaphysics clearly shows the unitary nature and coherence of Kant’s philosophical project.

In short, Gava’s book is an impressive work and a great contribution to the recent strand of Kantian scholarship that, including monographs such as Marcus Willaschek’s Kant on the Sources of Metaphysics: The Dialectic of Pure Reason (Cambridge University Press 2018) and Karin De Boer’s Kant’s Reform of Metaphysics: The Critique of Pure Reason Reconsidered (Cambridge University Press 2020), has paid and continues to pay increasing attention to Kant’s metaphysical concerns. A strand of which, in virtue of its several achievements, Kant’s Critique of Pure Reason and the Method of Metaphysics is a perfect example.