In my last posting on Rawls I looked at his response to "common sense" precepts of justice. There we discovered some reasons why "common sense" precepts are at the wrong level of generality to serve as primary principles of justice. However, Rawls concludes Chapter V of A Theory of Justice by considering two other alternatives to his argument for the two principles as the right ones to be adopted in the original position. In section 49 he addresses "mixed" conceptions of justice and in section 50 concludes with a response to the arguments that have been presented for a principle of political perfectionism. In this posting I will look at these arguments in turn.
At the opening of section 49 Rawls makes clear that the "mixed" conceptions considered are ones that require the adoption of the first principle of justice and, concomitantly with this, also agree to its lexical priority over the preferred second principle where this second principle is thought to have replaced the complicated conjunction of fair equality of opportunity and the difference principle that Rawls has advocated as required. So essentially the "mixed" conceptions supplement the liberty principle with something different than the directly egalitarian concerns Rawls has presented them with. An obvious example of a "mixed" conception would be a combination of the liberty principle with the principle of utility where, however, given lexical priority, the principle of utility would be subordinate to the liberty principle.
Such "mixed" conceptions would be in the classic position of intuitionist positions generally on Rawls' view which is that they would lack precision in application. You could, for example, view the second principle as a combination of "average" utility with some chosen minimum level of agreed income but it would still be an open question how to govern the relations between these elements. Effectively it might well be the case, Rawls suggests, that the difference principle would be being covertly appealed to in such a case. The difficulty here is much as with the appeal to "common sense" precepts which is that the intuitive nature of the combination in question leaves much undecided and without evident mechanisms available for decisions to be made. The difference principle, by contrast, allows for a direct form of appeal to be made in evaluation of decisions and this is a clear advantage of it.
Appeal to utility, even in a combined or "mixed" conception, constantly creates the problem of how the utility functions are to be measured. Maximisation has to include some measurement function and perhaps the most obvious one is the zero-one claim (everyone's preferences to count for one and no more than one). However this leaves a lot undecided between positive and negative outcomes and could lead, for example, to a preference for a large population that was relatively uneducated on the grounds that greater net utility was more easily achieved given greater numbers and fewer wants, an outcome that is, to say the least about it, not intuitive. (To see that Rawls' argument here is far from implausible it suffices only to consider what Parfit, in Reasons and Persons, termed the Repugnant Conclusion.) Generally speaking "mixed" conceptions that involve the principle of utility can be objected to both on grounds that they involve unacceptable uncertainty given their intuitionist basis and unacceptable risks given their utilitarian element.
In section 50 Rawls gives the principle of political perfectionism his attention and distinguishes between an absolute and a moderate variant of the principle. The "absolute" variant places a premium on the production of excellence above all else whilst the moderate version is a "mixed" conception that places the weight of excellence alongside other considerations. Essentially principles of perfection involve selection of certain types of lives as those which are given preference over others given their greater intrinsic value. Rawls terms this an "ideal-regarding" principle rather than a "want-regarding" principle. In one sense such a principle as that of perfection is close to Rawls' own endeavour since the principles of justice themselves are taken to have ideal requirements and to encourage certain types of character. But the principles of justice do not require reference to standards of excellence.
Principles of perfection would not be adopted in the original position on Rawls' view as there is no shared standard of perfection given in the original position. There is only an index of primary goods, which are assumed to be something all would want, not a standard of excellence which only some would aspire to incarnating or aiming towards. Only if a natural duty was assumed in the original position that was accepted as culturally viable could there be space within it for the choice of the principle of perfection. This does not mean that all activities will be taken to be of equal value but that there is not an assumption that the attainment of particular types of excellence will shape the basic structure.
The principle of perfection, if combined with another in the moderate "mixed" version, faces the familiar problems Rawls always poses to intuitionist views. Generally Rawls also considers the appeal to "excellence" to involve considerations that are distinct from those of justice. So, for example, appeals for certain kinds of prohibitions on behaviour (as with sodomy statutes) often require that particular ways of life be given special privilege but this consideration, given as such, has no obvious claim to be a just one. As Rawls puts it, "subtle aesthetic preferences and personal feelings of propriety" shape standards of excellence and these types of preference are not obvious bases for just evaluations.
With the rejection of the principle of perfection in both absolute and moderate forms Rawls concludes Chapter V, a conclusion that effectively closes his consideration of how the principles of justice relate to institutions in a general sense although, as we shall see, in due course, one very important question of institutional type is left for discussion in Chapter VI.