In Kant on Practical Life: From Duty to History, Kristi Sweet offers an interpretation of Kant’s practical philosophy as a whole, one that promises to provide ‘a sense of how it all hangs together’ (p. 7). The sheer scope of her book distinguishes it from most works of Kant scholarship. Her objective is to ‘articulate, in broad strokes, Kant’s comprehensive vision of practical life’ (p. 7). For a book of such scope, it is remarkably brief. In just over two hundred pages, she discusses nearly every aspect of Kant’s practical philosophy in an attempt to describe its unity.

I am of two minds about this book. On the one hand, I admire its ambition and I believe Sweet is right about the need for an overview of Kant’s entire practical philosophy. Kant’s writings on practical issues are scattered across many years and a wide range of works, from essays to systematic treatises such as the Critique of the Power of Judgement. This fact, combined with Kant’s terminological scruples and the density of his arguments, makes it very difficult to see ‘how it all hangs together’. Yet one cannot escape the sense that it does. The virtue of Sweet’s book is that it presents a provocative and relatively uncluttered interpretation of the entirety of Kant’s practical philosophy. This is no small accomplishment. On the other hand, Kant on Practical Life simply tries to do too much. Its briskness is a fresh change of pace. But because Sweet covers so much ground so quickly, she neglects to defend the exegetical merits of her interpretation or the philosophical plausibility of the views she attributes to Kant. The paucity of argumentation on either front is frustrating, and it diminishes the force of her two main claims.

The first main claim is that Kant’s comprehensive vision of practical life is deeply unified. The unifying theme is reason’s demand for the unconditioned. This is what ‘animates, authors, governs, and organizes the various aspects’ of Kant’s practical philosophy (p. 8). The introduction to Kant on Practical Life sets the stage with a discussion of this topic. Sweet explains how reason’s search for the unconditioned is due to its syllogistic nature, but also to the quasi-erotic way in which it drives rational creatures to satisfy the interests they have by virtue of being endowed with reason. She focuses on Kant’s treatment of the cosmological ideas, contending that the interests of reason find their satisfaction only in the idea of freedom, understood as the unconditioned condition of the world as a whole. But, according to Sweet, we can ‘discern’ in Kant’s treatment of the cosmological idea of freedom ‘something even deeper about reason’s demands’ (p. 34). Freedom, she claims, is ‘nothing other than reason’s causal force in the world. Thus what reason demands is not only the whole of nature, but that nature be, at bottom, rational. Reason, in the end, seeks itself in the natural order and cannot help but project an order that is rational’ (p. 34). Sweet develops this thesis by describing a kind of ‘movement’ through Kant’s work – from duty and the good will to virtue and the highest good, and from there outward to the social order (political, religious) and, ultimately, to culture and the course of history, where we ‘discern how nature itself contributes to reason’s ends’ (p. 11).

Kant certainly believed that the different uses of reason are unified by its underlying nature. But Sweet exaggerates the unity of his philosophy and his vision of practical life. Reason’s demand for the unconditioned in the theoretical realm is a demand for complete comprehension or understanding. This is a demand for a full and sufficient explanation of all appearances. Reason demands something analogous but importantly different in the practical realm. For any given maxim or policy of conduct, we can always step back and ask whether we are justified in doing what it prescribes. Reason’s demand for the unconditioned here is a demand for justification that neither requires nor admits of any further justification. Both demands are expressions of one and the same capacity (namely, reason) but it would be a mistake to think they are one and the same demand. From what I can tell, Sweet makes this mistake by claiming that reason’s drive for totality and completeness of theoretical comprehension drives the entire practical enterprise. Furthermore, her somewhat relentless focus on this theme obscures what John Rawls calls the ‘apologetic’ nature of Kant’s practical philosophy – his defence of common moral judgements and the self-understanding they entail. I see no evidence in Kant’s work that he believed our common moral judgements involved the demand that ‘the whole of nature’ be ‘at bottom, rational’ (p. 34).

The second main claim is that Kant’s vision of practical life is deeply social. Individual agents are social creatures, with histories and cultures, and reason’s demand for the unconditioned finds satisfaction only in ‘communal ends’ (p. 10). In emphasizing this side of Kant’s work, Sweet joins a salutary trend in the scholarship, which has done much to undermine the idea that his practical philosophy addresses itself to the solitary individual equipped with nothing but her own reason. Yet she goes further than most, claiming that ‘[t]he ends of reason are to be achieved only in the course of history. It is in history that we find both the development, refinement, and perfection of the use of reason and the absolution of finitude that nature imposes on us’ (p. 205). This remark is the culmination of the second half of her book (chs 3–6), which provides accounts of the highest good, the political order, religion, culture and history. Sweet is right to reject the caricature of the lone Kantian rational agent deciding how to behave by means of a one-size-fits-all ‘decision procedure’. But she goes too far. Kant’s moral philosophy gives pride of place to the mature rational agent – the individual person. The individual is autonomous thanks to her will, and elevated in worth above the rest of nature thanks to her autonomy. It is true that the individual is deeply embedded in a social and political order, but her autonomy gives her the authority to criticize its norms and rise above them. The most important ethical duties are those the individual has to herself, and no one can perfect her will for her. Nor can she perfect the will of another – just as a parent cannot make her child a better student by doing her homework for her (cf. MS 6: 386).Footnote ¹ Sweet sometimes acknowledges the importance of the individual person (e.g. p. 201), but these core aspects of Kant’s view are swamped by her emphasis on the social, political, cultural and historical.

The ‘apex of the book’ is the chapter on the highest good (p. 19) – which Sweet takes to be the ‘keystone and centerpiece of Kant’s practical philosophy’ (p. 8). Kant, we recall, thinks of the highest good as happiness distributed precisely in proportion to virtue. Sweet follows those who interpret the doctrine in social terms. According to her version of this approach, the happiness at issue is the happiness of the whole of the human race, not merely the individual agent. She identifies the highest good with what Kant calls in the Critique of Pure Reason a ‘moral world’, which is the idea of a world in perfect conformity with moral laws (e.g. KrV, A808/B836). Her social interpretation is supported by a number of passages from Kant, including his claim in the Religion that the highest good is a ‘good common to all’ (cited on p. 123). Since she accepts the claim that the highest good is a necessary end of practical reason, and because she associates the highest good with a ‘moral world’, she maintains that Kant’s practical philosophy ‘clearly indicates that the moral idea of the highest good requires the creation of a world through one’s will’ (p. 119). Sweet puts the point in very strong terms, claiming that reason demands ‘that, through my own will, I will a whole world; reason sets for me the task of creating the whole of what is through my actions’ (p. 142).

Her approach raises exegetical questions she does not answer. There are places where Kant does say that the issue is my own happiness. For instance, in the very discussion that frames Sweet’s entire approach, Kant describes two questions that concern the interests of pure reason and he says, ‘Now the second question asks: Now if I behave so as not to be unworthy of happiness, how may I hope thereby to partake of it?’ (A809/B837). The question of the individual’s ability to ‘partake of’ happiness is also at stake in the Critique of Practical Reason (e.g. KpV, 5: 110, 125). How does Sweet’s strongly social interpretation explain these passages? Her answer seems to be that the Religion passage, and others like it, makes explicit what was there all along (e.g. pp. 123–4). Yet this is only a reassertion of the social interpretation, not an argument in its favour.

Sweet’s approach also raises difficult philosophical questions. Consider the passage from the Religion she discusses on pp. 123–4. Speaking of the highest good, Kant writes: ‘Now, here we have a duty sui generis, not of human beings toward human beings but of the human race toward itself. For every species of rational beings is objectively – in the idea of reason – destined to a common end, namely the promotion of the highest good as a good common to all’ (RGV, 6: 97). This stirring remark does support Sweet’s social interpretation. But it cries out for elaboration and defence. How can the human race have a duty toward itself? How can the human race have any duties at all? Are these moral duties? If so, does this imply that the human race has a collective will and that this will has the property of autonomy? One also wonders how the entire species could ‘have’ an end. Is this anything like having an end that one sets for oneself? Finally if, as Kant claims, it is true that the very act of setting an end is an act of freedom, how could it be true that we are ‘destined’ or ‘determined’ (bestimmt) to have this end? One suspects that there are different senses of ‘end’ (Zweck) at work here, and it would be helpful to have a clearer sense of how the ends of nature relate to the ends and decisions of individual agents. It is also difficult to find in Sweet’s discussion a clear statement of how Kant’s doctrine of the highest good coheres with his account of autonomy and moral obligation. Many of his readers suspect that these ideas are deeply inconsistent. Given the centrality of the highest good to Sweet’s view, one would like to know whether those readers are mistaken. Her lack of engagement with these and other philosophical issues surrounding the highest good mars her treatment of the topic.

In sum, Sweet does not do enough to justify her two main claims. As a result, they seem like exaggerations that obscure the more modest side of Kant’s practical philosophy and the important role it assigns to the individual person. Still, there is much of value in Kant on Practical Life, and many readers will enjoy the opportunity to step back and try to take in Kant’s whole project at once. Kant scholars and other philosophers need books like this. Because of its brevity and lack of sufficient argumentation, Sweet’s book might not convince anyone who does not already share her views. But Kant on Practical Life works well as a ‘suggestion’ and a ‘framework’ for thinking about the unity of Kant’s project (p. 7).