The section opens by relating the general view of justice Rawls has set out to the Kantian conception of autonomy and emphasizes this conception over the place of universality and generality in Kant's ethics. The downgrading of the importance of universal law follows from an acceptance on Rawls' part of the force of the Hegelian objection of the "triviality" of the focus on universal law (although Hegel is not explicitly here referred to). In some respects this is surprising given the account Rawls gives subsequently of the "categorical imperative procedure" and is certainly not in accord with the work later done by constructivist interpreters of Kant.
However, whilst the downgrading of emphasis on universal law has problematic elements in it, there is also one basis for it that is creditable to Rawls and this is his intention to pay attention to the full scope of Kant's ethical view, a point made in an important footnote where Rawls wishes to distinguish Kant's view from the utilitarian conception of universality and attempts to easily reconcile Kant with utilitarian considerations. In making this point Rawls points, in a way that until extremely recently was unusual, at Kant's later ethical writings, particularly the Metaphysics of Morals although he also mentions the moral significance of Kant's works on religion and even refers to the Critique of Judgment. In the course of making this comment Rawls states that there was, at the time of writing Theory, 'no commentary on Kant's theory as a whole", adding, 'perhaps it would prove impossible to write'. Without saying that the work has addressed all elements of Kant's theory, since I am now certainly aware of a number that it does not, I think I can, without undue immodesty, point now to my own book, Kant's Practical Philosophy as covering rather more ground than any of the works Rawls here cites and going at least someway to disproving his pessimism concerning the possibility of addressing the ramifications of the whole theory.
Returning to the main text of section 40, Rawls' substantive philosophical point is to articulate the sense in which Kant makes moral principles objects of rational choice so that moral philosophy becomes the study of "the conception and outcome of a suitably defined rational decision". One of the points that Rawls derives from this is that understanding the point of legislation in relation to the kingdom of ends leads as a matter of course to the centrality of public principles although he neglects here to discuss the differing formulas of publicity Kant offers in Perpetual Peace. Free and equal rational beings are also presupposed in Kant's moral legislation.
Rawls articulates the original position as a way of realising the legislation of the kingdom of ends. One of the supporting considerations for this philosophical interpretation of the reference to the kingdom of ends is that Kant wishes to exclude heteronomous motivation and the adoption of the "veil of ignorance" ensures that the methodology of the original position maps this constraint. Effectively the ruling out of heteronomy is understood to require what Rawls earlier referred to as the formal constraints of right and the "veil of ignorance" is a means to ensure these formal constraints are met.
However, as Rawls goes on to add, there are additional elements in his construction that Kant does not refer to. One of the central ones is that of the basic structure although in referring to this Rawls neglects to follow the admonition of his own footnote since he doesn't mention here the formation of the basis of a state of right in Kant's Doctrine of Right but he does indicate generally that when all Kant's ethical writings are taken together something like the basic structure can be seen to emerge.
The principles of justice are also suggested to be analogous to the categorical imperative again when the latter is viewed primarily as a constraint that applies to persons understood as purely free, equal and rational. Just as the exclusion of heteronomy is mirrored in the "veil of ignorance" so also is the adoption of specific ends as required in hypothetical imperatives. However, Rawls does retain the notion of primary goods although he does assume these arise only from the most general assumptions about rationality and human conditions. The assumption of motivations in the original condition was also one of general mutual disinterest and this is again mapped in relation to the Kantian conception of autonomy.
Having made these points Rawls follows Sidgwick in identifying a problem with Kantian ethics, a 'problem' first articulated in the 'appendix' to the latter's Methods of Ethics. The 'problem' concerns an alleged ambiguity in Kant's view of freedom as on the one hand it is understood as a basis of choice whilst on the other it is also argued that choice of the law indicates a manifestation of freedom itself. This 'problem' has been examined at length since Rawls wrote this section of Theory with extensive accounts of the different types of freedom in Kant being undertaken by, for example, Henry Allison in his important book Kant's Theory of Freedom (amongst many other key treatments). It is a matter of distinguishing different ways in which Kant understands freedom that allows for the argument that "the scoundrel" as Rawls puts it does not realise freedom in the same sense as the one following the law and is far from being, as Rawls, following Sidgwick, thinks, a "decisive objection" to the Kantian view of freedom. Rawls says that Kant does not show "that acting from the moral law expresses our nature in identifiable ways that acting from contrary principles does not" but this is a mere assertion on Rawls' part since he does nothing to examine the evidence here.
It is likely far from being Rawls' case to engage Kant on this point since he wishes instead to articulate the original position as making good the alleged lack in Kant's view. Saying this does mean that the original position is taken to be an analogue to the noumenal view of choice with built-in constraints showing the ground for rational decision. In saying this however Rawls effectively reprises again the argument Kant gives not of moral choice in relation to autonomy but instead free choice in relation to right showing a surprising confusion of levels in Kantian theory afflicts Rawls' account. The description of the original position does not, as he claims, replicate that of noumenal freedom. Instead it replicates the contract position of right showing the ground for the restriction of external freedom being what can also realise it (the argument of his own previous two sections).
Rawls however is right to present Kant's view as one in which liberty is acting in accord with a law we give ourselves and that the understanding of shame, in Kant, is precisely one in which we fail to live up to such an ideal. The comprehension of Kant's view as an ethic of mutual respect is correct. The original position is presented in general by Rawls as a procedural interpretation of autonomy and the categorical imperative "within the framework of an empirical theory". One of the consequences of this is that Rawls does not investigate the notion that there is such a thing as pure practical reason. Another is that he conflates conditions of right with conditions of noumenal freedom. A third is that Kant's transcendental view is presented by Rawls as "transcendent", a mistake that is particularly striking. Finally, Rawls' view is explicitly distinguished from Kant's in the sense that whilst Kant's view applies to rational beings as such, Rawls' view is only meant to apply to human beings. The basic result of this is that Rawls gives up on providing a general theory of normativity or practical reason. One of the reasons for this is that Rawls wishes to give up on Kant's "dualisms", something that shows the philosophical modesty of Rawls' view. This modesty involves abstraction from central philosophical problems, an abstraction that much recent moral philosophy has, in my view rightly, given up on. The revival of more ambitious and comprehensive theories of practical reason is a return to the view of it that contemporary philosophers share with Kant and shows that the influence of Rawls on a central element of philosophy has waned.