In Kant’s Critique of Practical Reason: A Philosophy of Freedom, Otfried Höffe proposes to relate essential aspects of Kant’s practical philosophy to contemporary debates. Building on his reflections from the past three or four decades, he intends to answer the question ‘What in Kant still matters to us today?’, that is, ‘What can still be learned from Kant?’ (XIV). According to Höffe, Kant’s philosophy is essentially practical. The core of his book is that ‘all Kant’s critical thinking is ultimately about morality and freedom’ (XII). Höffe expounds not only on morality but also on political philosophy, philosophy of history, religion, and education.

Originally written in German, the book’s first English edition is abridged and updated. Höffe adds a new chapter, ‘A Look at the More Recent German Debate’, and expresses his concerns regarding the fact that many Kant scholars do not think it is essential to read German and considers this ‘testimony to a great loss of quality in the international debate on his [Kant’s] work’ (p. 230). He highlights contributions written in German regarding the edition of Kant’s works, a lexicon, collective commentaries on Kant’s texts, and monographs written by German and by other, non-native German-speaking scholars, mainly Asian. The Afterword is dedicated to some ‘particularly worthy’ Anglophone contributions.

The book is divided into four main parts. They are preceded by a preface and an introduction. In the Introduction, Höffe presents four motivating forces which he sees as indispensable for Kant’s philosophy and also for contemporary civilisation. They are (1) ‘the Enlightenment, defined principally as thinking for oneself’, (2) ‘the Methodological goal of a critique in the style of a judicial trial’, (3) ‘Morality as the leitmotiv already defining the first Critique’, and (4) a ‘Comprehensive Cosmopolitanism’ (p. 1) – ‘comprehensive’ because it is broader than its currently political meaning since it is grounded in universal human reason, transcending all political boundaries.

These motivating forces are not separated but rather linked to each other by Kant’s three well-known questions: ‘What can I know?, What should I do?, and What may I hope?’. Accordingly, Höffe dedicates the Introduction to explaining how each one of the motivating forces is intertwined with morality. He confesses to having a heretical reading when declaring that the Critique of Pure Reason is not interested in knowledge but in morality (pp. 7, 11). Yet, he justifies his reading by referring to the B Preface to the first Critique (BXXXI), where Kant claims that ‘philosophy ultimately serves the only necessary purpose: morality …’ (p. 7). As a positive answer to the question ‘What in Kant still matters to us today?’, he concludes that Kant’s comprehensive cosmopolitanism, together with morality, is ‘highly significant for a world that is becoming ever more globalised’ (p. 14).

In Part I, entitled ‘Kant’s Revolution of Moral Philosophy’, Höffe deals with the revolution of Western moral philosophy in two steps: one is destructive, in which Kant rejects the principle of eudaimonia and its occasionally alternative principle of theonomy as the supreme principle of morality; the other is constructive (or reconstructive), in which Kant replaces these rejected principles with the principle of autonomy. Höffe emphasises that this constructive step in Kant’s argument cannot be confused with the alleged constructivism in Kant’s moral philosophy. In his reading, Kant’s philosophy has instead ‘the character of a reflexive self-enlightenment of moral consciousness’ (p. 16). He remarks that even John Rawls ‘rightly sees that the categorical imperative is not constructed but “unfolded”’ (p. 15).

Höffe considers central and thorny themes and concepts of Kant’s moral philosophy: the categorical imperative and its formulas, maxims, freedom of the will, the fact of reason, the feeling of respect, and the unity of reason. He didactically reconstructs Kant’s argument for morality in the Critique of Practical Reason, pinpointing each of its seven steps. In concluding Part I, Höffe expresses what moral modern philosophy can learn from Kant, such as awareness of the problem ‘what is morality?’ and the advantages of a moral philosophy based on maxims.

In Part II, entitled ‘Kant’s Provocations’, Höffe examines some elements of Kant’s moral philosophy that, according to him, have not received the attention due them in the contemporary debate on ethics. Among these elements are (1) the idea of the highest good and, connected with it, the feeling of respect and the postulates of practical reason, (2) the contrast between duty and inclination and Schiller’s criticism of Kant, and (3) the claim that metaphysics is essential for convincing moral justification. In this third ‘provocation’, Höffe expounds on the relationship between Kant’s and Aristotle’s moral philosophies. Although Kant revolutionises moral philosophy with the principle of autonomy, Höffe claims that ‘due to a number of fundamental similarities, Kant proves to be an Aristotelian in the way that he practises moral philosophy’ (p. 130). One of these similarities is that Kant’s as well as Aristotle’s ethics are metaphysical yet free of metaphysics, which means that both ethics are ‘genuinely practical fundamental philosophy independent of theoretical fundamental philosophy’ (p. 138).

In Part III, entitled ‘World Politics and World History’, Höffe deals with Kant’s political philosophy and his philosophy of history, especially with the idea of eternal peace, the cosmopolitan philosophy of history, and the ‘great artist nature’ (natura daedala rerum, ‘Perpetual Peace’, 8: 360), which guarantees perpetual peace. Höffe lists six ‘provocations’ that characterise Kant’s political philosophy as seen from today’s perspective, such as Kant’s defence of a categorical imperative of law and metaphysics as an essential requirement.

In Part IV, entitled ‘Religion, Education and the Final End’, Höffe completes the study of Kant’s practical philosophy by examining Kant’s views on religion, education, and the thesis of the human being as the final goal of history. Höffe recalls that the ultimate purpose of education is the development of freedom and morality. Since ‘a human being can only become human through education’ (p. 214), any study of Kant’s practical philosophy of freedom and morality would not be complete without examining Kant’s views on education. Regarding religion, Höffe’s interest focuses on Kant’s claim that ‘morality inevitably leads to religion’ (p. 191). He didactically summarises the main topics that Kant considers in Religion within the Limits of Mere Reason and presents the novelty of Kant’s interpretation of the Christian doctrine of original sin and the connection between evil and freedom in human beings. Höffe concludes Part IV by expounding on Kant’s claim that the human being is not only an end in itself, as stated in the Groundwork for the Metaphysics of Morals, but also the absolute final end of all nature insofar as he is a moral being, as stated in the Critique of Judgement.

Kant’s Critique of Practical Reason: A Philosophy of Freedom is an extensive book in terms of the topics it covers. It could benefit both Kant scholars beginning to work on any theme of Kant’s practical philosophy and those who want to read Kant as a reference to contemporary questions on ethics in a broad sense. Höffe’s motto is ‘I Kant get no satisfaction’ (p. XII). Accordingly, extension and intension are symmetrically opposed in Kant’s logic, and sometimes breadth and depth cannot be found at the same time in Höffe’s book. Since it is impossible to do justice to all the themes dealt with in its almost 300 pages here, I will only gesture towards some general questions regarding three problematic topics that Höffe does not seem to explore in great detail: (1) the unity of reason, (2) the relationship between Kant’s argument in Groundwork III and the fact of reason in the second Critique, and (3) that Kant’s political philosophy supposedly amounts to liberalism.

The primary problematic topic is that it is not obvious, as Höffe states (p. 18), that in the Critique of Practical Reason Kant dedicates himself to and succeeds in presenting the unity of reason:

Further on (p. 112), Höffe mentions that ‘the worlds of nature and morality … harmonise in the unity of the highest good’. Finally, he declares (p. 163) that ‘in his [Kant’s] view, there are only three basic human faculties: the faculty of cognition, the faculty of desire, and the power of (reflective) judgement (CoJ, V, 176 ff.) that is “mediating” their “connection”’. Höffe, however, does not expound on or clarify whether this ‘mediating’ role of the power of reflective judgement and the ‘connection’ between the faculty of cognition and the faculty of desire can be related to the task of unifying pure practical reason with speculative reason. Neither does he explain how the highest good plays a role in fixing ‘the gulf between nature and freedom’, the domains of theoretical and practical philosophy (cf. CJ, 5: 175–6). So, in what sense do the ‘keystone’, ‘the highest good’, and the ‘power of reflective judgement’ refer to and solve the same problem of the unity of reason?

In the Preface to the Groundwork, Kant settled the unifying task as indispensable to completing the critical examination of pure practical reason (4: 391) but left this task unfinished there. So, it seems natural for any reader to expect to find this accomplishment in the second Critique. However, Kant seems to postpone this task once again by treating it as an ‘expectation of perhaps being able some day to attain insight into the unity of the whole pure rational faculty’ (5: 91). It is hardly surprising, then, that there is no consensus in the literature on whether Kant attains this unity and, if he does, on what this common principle that unifies the whole pure rational faculty is.

Among the differing interpretations, Onora O’Neill (Reference O’Neill and O’Neill1989) defends the thesis that the categorical imperative is the highest principle of both theoretical and practical reason, and Patricia Kitcher (Reference Kitcher2011) offers additional evidence in favour of O’Neill’s thesis. Heiner Klemme (Reference Klemme2014) challenges this thesis and argues that the ‘common principle’ is the reflective power of judgement. Henry Allison (Reference Allison and Allison2012), addressing the problem in terms of the gulf between freedom and nature, argues that it can be fulfilled only in the third Critique with the reflective power of judgement and its principle of purposiveness of nature. Pauline Kleingeld (Reference Kleingeld1998) argues for the purposiveness of nature, emphasising the primacy of practical reason and Kant’s solution before the third Critique. Similarly to O’Neill and Kitcher, Sasha Mudd (Reference Mudd2013) advocates for the priority of practical reason, arguing that the categorical imperative is the supreme regulative principle of reason, and Lara Ostaric (Reference Ostaric2023) argues that the unity of theoretical and practical reason results from subordinating theoretical judgement to practical cognition. Karl Schafer (Reference Schafer2023) addresses the problem of the unity of reason in terms of the unity of comprehension (Begreifen) and autonomy, emphasising that he treats theoretical and practical reason as coequal manifestations of reason’s fundamental form of activity. In the late 1970s, Klaus Konhardt (Reference Konhardt1979) had already argued that theoretical and practical reason share similarities and that the essence of the problem of the unity of reason was in the first Critique and without ‘essential modifications’ in the third Critique. The dispute is immense, the approach to the problem is ambiguous, and Höffe’s solution seems to be ambiguous, too. If his interpretation changed over the years, what is Höffe’s current thesis?

The second problematic topic regards the relationship between Kant’s argument in Groundwork III and the fact of reason in the second Critique. Höffe presents his reading of Kant as heterodox, even heretical, but it is not clear whether he is heterodox and denies or is orthodox and embraces the interpretation of the great reversal from the Groundwork to the second Critique. Höffe states that the Critique of Practical Reason is higher in philosophical significance in comparison with the Groundwork and lists four reasons for that, among them that the second Critique ‘states its problem more clearly, is more precise in its terminology and more direct in the way that it tackles its problem’ (p. 18). He emphasises that this applies especially to the ‘Analytic of Pure Practical Reason’, where Kant develops his argument of the fact of reason. Höffe pinpoints each of the seven steps of the argument and claims that ‘the theorem of the fact of reason indicates reality’ (p. 29). He states that in the first Critique, Kant deals with the conceivability of transcendental freedom, and in the second Critique, with its reality (p. 18), that is, with its objective reality, which leads to autonomy (p. 33). It is uncontroversial that conceivability in the first Critique means logical possibility. However, Höffe does not make clear what he means by the terms reality or objective reality. Does reality mean real possibility or actuality (Wirklichkeit)? The actuality of something means its existence in space and time; the objective reality in a practical sense determines an action as if something were real, even if it is not possible to prove the actual existence of this something. If by reality or objective reality, Höffe understands, on the one hand, real possibility, Kant has already justified that with the deduction of the categorical imperative in Groundwork III (see, for instance, Wood Reference Wood2020 and Reference Wood, Filieri and Møller2024). So, how should we understand the appeal to the fact of reason? If, on the other hand, by reality or objective reality, Höffe understands actuality, and the arguments from the Groundwork and from the second Critique have different objects and roles, then what is Höffe’s position on the great reversal?

Finally, the third problematic topic regards what Höffe considers one of Kant’s ‘provocations’ within the philosophy of law and state, namely, that ‘politically speaking, the theory of law and state based on this imperative [the categorical imperative of law] amounts to a liberalism that favours the rule of law, and it allows the welfare state only to the extent that it serves the rule of law’ (p. 139). Again, there is no consensus about this in the literature. Allen Wood (Reference Wood2014: 84) argues that ‘Kantian right is sooner socialist than libertarian’ because its aim is to protect the basic rights of every citizen in the name of freedom, not in the name of welfare. He refers to interpreters who defend a libertarian reading, such as Mary Gregor and Robert Nozick, and to interpreters such as Hermann Cohen and Karl Vorländer, among others, who, like him, defend the position that Kantian right ‘would sooner result in a social democratic state’. Höffe does not develop this ‘provocation’ in this new book, nor does he mention the dispute in the literature. This suggests that Höffe’s book results from courses and lectures he gave over the last thirty or forty years.