This volume contains twelve newly commissioned essays by leading scholars in the field. The book is not intended as a commentary. Its purpose is to shed light on aspects of Kant's final major work in moral philosophy – a work whose internal coherence, place in the corpus, and relevance for ethics and political philosophy have long been a matter of dispute.

Manfred Kuehn opens with a reconstruction of the history of postponements, interferences and transformations that culminated in the 1797 Metaphysics of Morals. This history can be divided ‘into three periods, with the first one dating from 1762 to about 1770, the second one from 1770 to 1785, and the third period from 1785 to 1797’ (15). Over such a long haul Kant's views underwent numerous changes, and it is unclear whether the final product reflects his initial intentions. There are two opposing schools of interpretation. They emphasize either the continuity or the break with Kant's pre-Critical views. Kuehn strikes a middle ground. In his reading, ‘[w]hat remained the same is the actual content of Kant's Rechts- and Tugendlehre. What changed was the perspective from which this content must be viewed according to Kant’ (16). Although these changes raise tensions, they do not undermine the integrity of Kant's project.

Stephen Engstrom develops a ‘practical-cognitivist’ interpretation of the Kantian will. Through a close reading of the introductory section on the faculty of desire (6: 211–14), he argues that the will for Kant combines a cognitive (rational) and a desiderative (causal) element – it is, quite literally, practical reason. An act of volition is a type of judgement, ‘the conclusion of a practical syllogism in which reason is employed to derive an action from a law’ (33). Kant's picture thus turns the Humean model on its head: instead of construing reason as inert and desire as externally determined, Kant views reason as efficacious and desire as rational. Using this framework, Engstrom reinterprets Kant's distinction between Wille and Willkür. I remain doubtful about how this interpretation can respond to the challenge of radical evil: the self-imposed propensity that corrupts reason at its core cannot, to my mind, be discounted as mere cognitive failure.

In her insightful ‘Justice without Virtue’ Katrin Flikschuh revisits the debate about the moral status of the Doctrine of Right. She argues in defence of the irreducibility of justice to Kantian morality. The originality of her view lies in its emphasis on the omnilateral character of the general united will. This is necessary to supersede the state of nature, but entails a form of willing altogether different from the private capacity for self-legislation characteristic of morality. Flikschuh thus takes issue with contemporary liberals who, inspired by Rawls, are insensitive to this fundamental difference: liberals ‘have taken the categorical imperative of the Groundwork to offer a decision-making procedure for the generation of valid principles of justice, and … in so doing have transformed Kant's ethics of self-legislation into a political morality of co-legislation’ (52). For Flikschuh, this picture misrepresents the political situation. By eliding the distinction between autonomy and freedom, liberals overlook ‘Kant's categorical distinction between private and public willing and lawgiving within the domain of Right’ (66). The latter is captured by external freedom, whose laws have objective necessity independently of our subjective (private) acceptance. Here one is free but not autonomous, for Wille and Willkür are not located in the same agent. Such dislocation does not mean that juridical laws are arbitrary, ‘for the general united will makes laws in accordance with a priori principles of Right’ (59). All it means is that private maxims are not identical with coercive laws.

Kant claimed that there is only one innate right, the right to freedom (6: 237). Otfried Höffe shows how this single right can ground a plurality of human rights.

What motivates these distinctions is the insight that ‘no purely positive legal order can uphold itself; it requires a foundation beyond positive law, a supra-positive foundation’ (75). In Höffe's reading, the idea of humanity provides that foundation: ‘only those who refuse to be simply instrumentalized and fundamentally degraded in matters of right become legal entities’ (86). This has a surprising consequence: an ethical duty (respect for the dignity of our own humanity) precedes and grounds our legal standing.

Sharon Byrd discusses Kant's account of the right to own external objects. The innate right to freedom, Byrd notices, authorizes us ‘to move around without restriction with our own bodies’, but this ‘does not give us the right to have external objects of choice as our own’ (93). To explain the emergence of this latter right, Kant introduces a postulate of practical reason (6: 246). Commentators have usually taken the postulate as a law providing justification. But Byrd argues that this is misguided: there is nothing wrongful (in need of justification) about taking something external as one's own – what is wrongful is to leave them things masterless. Byrd proposes, therefore, to take the postulate as a power-conferring norm. Such a norm does not depend on the existence of the state, but on ‘the universal a priori united will of all, the will of the original community of the earth with its goal to divide the land and the things upon it to avoid constant conflict’ (110).

Allen Wood examines two main sources of tension within Kant's theory of punishment. First, although Kant openly subscribes to retributivism, he offers no proper justification for this view. Instead, he justifies punishment ‘as a form of coercion used to protect right. But this is not in the least a retributivist justification’ (120). Second, and perhaps more troubling, Kant's retributivism is at odds with other basic commitments of his ethical theory. The law of punishment, for example, makes its end the infliction of proportional harm on the criminal. But this ‘seems to be in direct conflict with the basic ethical principle that the happiness of others is a duty of virtue’ (122): we are required by a juridical duty to make our end the unhappiness of another – precisely what the duty of beneficence prohibits us to do. For Wood, this kind of tension is disheartening, because retributivism is the best guarantee against abuses other theories of punishment generally condone.

I now turn to the essays concerned with the Doctrine of Virtue. In the Introduction to the latter, Kant mentions four ‘aesthetic preconditions (Vorbegriffe) of the mind's receptivity to concepts of duty as such’: moral feeling, conscience, love of one's neighbour and respect for oneself (6: 399–403). How can these aesthetic prerequisites work as incentives of morally worthy actions? How do they relate to the single feeling of respect that occupied Kant heretofore? In Paul Guyer's interpretation, Kant's transcendental idealism licenses us to give a strictly empirical account of the role of feelings in the phenomenal aetiology of moral action. So construed, the ‘aesthetic preconditions’ offer a multistage explanatory model. The first stage is ‘moral feeling’, which roughly coincides with what Kant formerly called ‘respect’. To make the moral law effective, Kant now realizes, moral feeling needs to be cultivated and strengthened. This is the role of the other preconditions: conscience leads us to hearken to particular moral maxims, and sympathy and self-respect to draw on our natural dispositions to promote other- and self-directed actions. While this empirical account is ‘interesting and promising’, Guyer concludes, the metaphysical story Kant devised to underpin it can be safely thrown into the ‘dustbin of history’ (151).

In ‘What is the Enemy of Virtue?’ Jeanine Grenberg discusses a striking ambiguity in Kant's account. While in the Doctrine of Virtue inclinations (understood as natural forces) seem to play the part of enemy, in Religion inclinations ‘considered in themselves … are good’ (6: 58). Evil is an ‘invisible enemy… who hides behind reason’ (6: 57). Grenberg contends that, properly understood, Kant's two positions are compatible. For inclinations are integrated into the ends humans set (6: 380–1), and setting ends is the ultimate act of freedom. Consequently, in both texts the enemy of virtue is vice.

Lara Denis discusses perfect duties to oneself (PDS). Violating these duties, Kant argues, renders us incapable of fulfilling other obligations and unjustified in demanding respect from others. Although PDS forbid certain actions (enslaving oneself, servility, lying, etc.), they are ethical duties, since they do not impinge on the external freedom of others. Denis notices significant variations in Kant's account of these duties. In the Collins lectures, PDS prohibit ‘acting against necessary conditions of one's greatest, self-consistent use of freedom’ (174–5). In the Doctrine of Virtue, they prohibit ‘opposition to one's moral self-preservation and moral health’ (176). In Vigilantius, they are grounded in ‘the right of humanity in our own person’ (178). Despite their differences, Denis argues, these accounts are united in their depiction of PDS as bearing tighter, more urgent or more fundamental relations to freedom than other types of duties – hence their primacy in Kant's moral theory.

For Kant, the duty of beneficence is wide or imperfect. According to Robert Johnson, this commits him to two claims: ‘(1) we have an ethical obligation to others to adopt their happiness as our end, and (2) normally no particular person has a claim on our assistance in advancing her happiness’ (192). The problem is that Kant's distinction between duties to and regarding others entails a third claim that challenges the traditional understanding of imperfect obligations. For ‘(3) you have a duty to someone to do something if and only if that person has some claim or right that you do it’ (193). Attributing such a right to others, however, brings the duty of beneficence suspiciously close to a perfect duty. Johnson appeals to the idea of a ‘collective right’ to reconcile Kant's three claims. In his reading, others have a collective right to my adopting their happiness as my end, even though no particular individual can demand that I make her happiness my end. Others, then, can hold me accountable for not adopting an end that it is my duty to have, but those whom I actually help and those who can hold me accountable need not be the same people (205). The problem I see with Johnson's reconstruction is that it attributes to others a capacity only God could have, namely, that of being able to judge my adoption of ends.

Kant infamously claimed that we have duties with regard to animals but not to them. Patrick Kain argues that ‘[a] better appreciation of Kant's commitments in a variety of disciplines reveals that Kant had a deeper understanding of human and non-human animals than is generally recognized and will help address, at least from Kant's perspective, many of the familiar objections to his account of “duties regarding animals” ’ (211). Against the standard criticism that Kant's concern for animals is purely instrumental, Kain shows that ‘Kant's emphasis is upon what mistreatment of animals expresses about one's feelings and moral perfection, rather than on the effects of mistreatment’ (226). More importantly, Kant recognizes that something about the animals in question justifies the demand to treat them decently: ‘because of their nature or behavior, animals are the proper object of one's sympathy and love’ (226–7). These feelings are morally significant, for they belong to the ‘aesthetic preconditions’ of our ‘receptivity to concepts of duty as such’ (6: 339).

Thomas E. Hill closes the anthology. He engages in a general discussion of Kant's normative ethics, the role of basic moral principles, and the wide-ranging implications of the duties to oneself. This ties together many themes that run throughout the book and gives it a sense of unity.

In sum, Kant's Metaphysics of Morals: A Critical Guide is an excellent volume that will contribute to our understanding of Kant's practical philosophy. It makes more accessible a book that remains largely unknown for many Kantians, but which Kant conceived as the culmination of his efforts.