Though Rawls's Theory of Justice is noted for its famous neutrality concerning the good, Rawls does present in Part 3 a sophisticated and plausible account of the personal good - what makes a good life good. Indeed, it seems to me, Rawls's view as presented provides valuable insight into similar, though competing, accounts of the personal good put forward by the 19th Century British idealists, most notably T. H. Green. Though their views differ only slightly, it seems to me that where their views differ, Rawls wins.
Rawls defines the notion of the personal good in terms of life plans. In section 63, Rawls writes: "first, a person's plan of life is rational if, and only if, (1) it is one of the plans that is consistent with the principles of rational choice when these are applied to all the relevant features of his situation, and (2) it is that plan among those meeting this condition which would be chosen by him with full deliberative rationality, that is, with full awareness of the relevant facts and after a careful consideration of the consequences." Rawls then narrows the account down slightly: "we should expect that the good things in life are, roughly speaking, those acitivites and relationships which have a major place in rational plans." Rawls claims that this definition is merely an application of Sidgwick's account of the good, which he glosses as "what [a person] would now desire and seek if the consequences of all the various courses of conduct open to him were, at the present point of time, accurately forseen by him and adequately realized in imagination." Thus the personal good, for Rawls, are those major elements of what one would desire under suitably idealized cognitive conditions 1) full information and 2) full awareness of that information.
Now compare the account of the good offered by T. H. Green. Green calls the personal good alternatively "self-realization" or "self-satisfaction." In a short essay, "The Senses of Freedom," Green writes: "His will to arrive at self-satisfaction not being adjusted to the law which determines where this self-satisfaction is to be found, he may be considered in the condition of a bondsman who is carrying out the will of another, not his own. From this bondage he emerges into real freedom, not by overcoming the law of his being, not by getting the better of its necessity - every fancied effor to do so is but a new exhibition of its necessity - but by making its fulfillment the object of his will; by seeking the satisfaction of himself in objects in which he believes it should be found, and seeking it in them because he believes it should be found in them." Of course, Green here is talking about the notion or freedom or autonomy. Someone is free if and only if the objects they seek are sought under the guise of the good. But his account of self-realization takes this to heart. From Prolegomena to Ethics, section 176: "And hence the differentia of the virtuous life, proceeding as it does from the same self-objectifying principle which we have just characterized as the source of the vicious life, is that it is governed by the consciousness of there being some perfection which has to be attained, some vocation which has to be fulfilled, some law which has to be obeyed, something absolutely desirable, whatever the individual may for the time desire; that it is in ministering to such an end that the agent seeks to satisfy himself." Again, what we seem to have operating here is the notion that what is good for a person is seeking good things under the guise of the good, by recognizing and developing one's understanding of the moral law or the notion of intrinsic value and acting accordingly. David Brink glossess self realization in the following way: "Responsible action involves self-consciousness and is expressive of the self. The self is not to be identified with any desire or any series or set of desires; moral personality consists in the ability to subject appetites and desires to a process of deliberative endorsement. So the self essentially includes deliberative capacities, and if responsible action expresses the self, it must exercise these deliberative capacities."
These two accounts of the good may seem radically different, but they have quite a lot in common. One reason for this is the reliance on deliberative rationality in Rawls. In order for an aspect of one's life plan to be good, it must pass deliberative muster - in other words, it should be endorsed in idealized conditions, i.e., with full awareness of all relevant information. But this form of endorsement appears to be something like evaluative endorsement. When I endorse something from within those idealized conditions, the only way in which I have to endorse or not endorse those options are via evaluative concepts. Given that X has consequence Y, and W has consequence Z, and I regard Y as more valuable than Z, I deliberatively endorse X. (This leaves aside the possibility that I might, under certain warped psychological conditions, endorse Z because with full information I endorse all and only those things that fall under the guise of the bad. But Rawls's account could be modified to account for this possibility - i.e., only those things I deliberatively endorse as good are good for me) Rawls's deliberative rationality seems to be a psychologically descriptive proxy for Green's insistence on endorsement under the guise of the good.
One objection to this alignment might be to lean on Rawls's endorsement of the good life of the grass counter. Rawls imagines someone who is fully committed to the activity of grass-counting, and organizes his life plan around that activity. "perhaps he is peculiarly neurotic and in early life acquired an aversion to human fellowship, and so he counts blades of grass to avoid having to deal with other people. But if we allow that his nature is to enjoy this activity and not to enjoy any other, and that there is no feasible way to alter his condition, then surely a rational plan for him will center around this activity." This might seem out of congruence with Green, especially given that Green is widely regarded as a perfectionist, someone who holds that certain activities just are less valuable for people, regardless of their first-personal assessment of that value. However, this is too quick. There is no reason why we should believe that Green would reject the value of the grass-counting life for the grass counter. Again, in "The Senses of Freedom," Green writes: "freedom is the natural term by which the man describes to himself the state in which he shall have realised his ideal of himself, shall be at one with the law which he recognizes as that which he ought to obey, shall have become all that he has it in him to be, and so fulfil the law of his being or live according to nature." But surely the grass counter is living according to his ideal of himself. Grass-counting simply happens to be his ideal. It is deliberatively endorsed under the guise of the good. He fulfills the law of his being by subjecting his desires to deliberative endorsement, which results in a desire for grass-counting. This should not cleave Rawls and Green. (Of course, one might claim that Rawls and Green differ because Green has the capacity to insert in his account a notion of the good that is independent of the agent, and that an activity is self-realizing if and only if it conforms to this notion of the good. I leave this suggestion to the side.)
However, there is one important distinction. For Rawls, the good life for someone is one that is lived according to a rational life plan, and that rational life plan is one that would be endorsed under suitable conditions. The key is the modal operator. Rawls does not require that a good life actually engage in deliberative rationality or deliberative endorsement. One need not come into contact with one's conception of the good to live a perfectly good life. One need only live according to a life that would be so chosen. Rawls: "It is not inconceivable that an individual, or even a whole society, should achieve happiness moved entirely by spontaneous inclination. With great luck and good fortune some men might by nature just happen to hit upon the way of living that they would adopt with deliberative rationality." But being guided by one's inclination is absolutely ruled out by Green. In order for someone to achieve self-realization, he or she must engage those capacities that affect one's deliberative endorsement, one must actually deliberatively endorse. Otherwise, according to Green, the agent is not free and is thus not self-realizing. The extent to which value is achieved is heteronomous, not autonomous.
Thus the key distinction between Rawls and Green is a modal one. Rawls only requires hypothetical deliberative endorsement, Green requires actual deliberative endorsement. Which is more plausible?
It seems to me that Rawls bests Green on this controversy. Imagine two lives, A and B. These lives are totally isomorphic. The difference is only that A lives his life according to spontenaiety and whim, B plans and reflects. A's desires just happen to correspond to the desires that would be produced under deliberative endorsement. Of course, the projects they end up pursuing are identical, and indeed, the projects they pursue are totally reflective of their conceptions of the good (though only B engages that conception of the good). Is it the case that A's life is worse than B's? It seems to me that the answer is clearly no. A is able to live according to activities that are in no way out of congruence with his or her conception of value, as is B. But why should the mere fact that B has checked antecedently to make sure this is the case affect his well-being score by such a large degree? It seems to me that refusing to grant the value to A that B has is fetishizing rationality and deliberation. The value of one's activities, it seems to me, is to be found in the activities and their contribution to the value of one's life. The value of the activities is not to be found in their being valued by the agent who engages in them. Of course, B might have a certain peace of mind that A doesn't have (i.e., doesn't have all those nagging questions: "Should I really have done X?"). But this can be factored out of the example. Assume that the lives are precisely identical in terms of peace of mind, etc. My intuition is that the lives are of identical value. This can be seen by noting the intuition that A's alignment of desires is extremely lucky: A hits on a life of value without worrying about deliberating one way or the other. A is blessed.
Perhaps you disagree. But surely it's the case that the life of A is of great value, if not as great as B's. But I don't see how Green's account can accommodate this. Without deliberative endorsement, there is no self-realization. It seems to me that Green's view must say that A's life is of no value at all (or, perhaps of extremely minor value, hedonic value only, say). But this seems radically wrong to me. Achieving things of value by instinct, say, and good fortune is no worse for one than achieving good things by deliberative contemplation under the guise of the good.
I guess I don't have a strong argument here, that's just my intuition.