Griffin's idea of the relation between morality and prudence is complicated. He wants to allow both the existence of a sense in which lives can be said to be good which is prior to the moral sense and the "penetration of the prudential by the moral", namely the fact that being virtous or acting morally can be intrinsically prudentially valuable; in addition to this a deflationist view about "dualism of practical reason". I believe that it is very difficult to come up with a coherent notion of well-being, compatible with these ideas.
The penetration of the prudential by the moral. (p. 131)
“What I have in mind is this. One has not got a specification of the prudential at all without a pretty full account of what moral demands there are on us and how they are to be accommodated. Prudential value does not stop at the edges of an individual’s own private life. Some persons may see their self-interest in a narrow, crabbed way. But anyone with a defensible idea of prudential values can see what he cares about not just as what as a matter of fact he now cares about, but as what he ought to care about or what he will care about after subjecting his concerns to full deliberations. He will find it hard, therefore, to keep moral and prudential values apart. One of the things he will want is a life of point and substance. What he will see as prudentially valuable, valuable to his own personal life, will to some extent coincide with what he will see as valuable morally. Our understanding of ‘a good life’ cannot be parcelled into ‘good prudentially’ and ‘good morally’. The very phrase ‘ a good life’ may seem ambiguous (good prudentially? good morally?), but at any deep level there are not two senses to be distinguished. Part of having a life of point and substance is having a life in which moral reasons take their place, along with other practical reasons, in motivation.” (131)
[He endorses this for the sake of the argument. Apparently this conception seems to be rejected by those other arguments. But he does not appeal to the previous arguments. Rather, Griffin endorses this claim for the sake of the argument, and shows that even if it is true, in this way one cannot attempt to reduce morality to prudence, since prudence is already defined in moral terms.].
Thus, Sigdwick's dualism of practical reason has to be rejected:
“And since we want to live a life of value or weight, we have to decide what a valuable life is. This is a point, among many others, at which prudence and morality will not stay apart. A valuable life, in the sense that we are now trying to understand, cannot just be a life filled with prudential values conceived in fairly narrow self-interested terms. A valuable life, in the sense we are after, consists importantly in doing things with one's life that are themselves of sufficiently substantial value to turn back on the life itself and make it valuable. And we cannot see what we do in those necessary terms if we have no regard for, or if we damage, values generally, including the value of other persons' lives.[...] Prudence cannot be kept in narrow confines. What is prudentially valuable must, at various points, spread out into areas that do not look like a part of prudence at all. The boundary defining prudence cannot, along this frontier, really be fixed.” (156-157)
Why does Griffin thinks that the rejection of dualism does not favor the idea that ethical push and pull eventually meet? Here is what he writes.
“Furthermore, the penetration of prudence by morality, in particular that it penetrates it in a way that shifts serious deliberation on to the level of abstraction where the categories 'prudential' and 'moral' are left behind, makes dualism an unlikely model for their relation. This is not to say that ethical push and ethical pull eventually meet; so far as I can see it points to the opposite conclusion.” 160
Griffin also makes a point that is anaologous to the one made by Scanlon in “what we owe...”, about the idea that there is type of deliberation in which reasons of prudence are evaluated together with reasons of morality.
“But the most important point to make about the putative dualism of practical reason is that deliberation of a sufficiently global scope is not conducted in terms of ‘prudence’, ‘self-interest’, or ‘flourishing’ on the one side and ‘morality’ on the other. It is conducted in terms of strength of practical reasons. […] It is to say that values, neither expressly prudential nor expressly moral but values taken at a higher level of abstraction, are what we appeal to: the notion f what , all things considered, is worth our concern. Just as when with prudential values we deliberate not by appeal to any one substantive prudential value but to the notion of prudential value itself [when is it the case that we do this?], here too we step up another rung in the ladder of abstraction. There is nothing mysterious or suspect about this step; it is one more of the same sort that we have continually taken in deliberation.” (161)
The big difference between this view and the view argued by Scanlon is that Griffin thinks that the above described type of practical deliberation, which may be called "deliberation about the kind of life one should live" represents the next "step up" "in the ladder of abstraction", after one in which "with prudential values we deliberate not by appeal to any one substantive prudential value but to the notion of prudential value itself". Scanlon, on the contrary, argues there is no level of deliberation in which we appeal to the notion of prudential value itself, rather than to any one substantive prudential value.
Also Griffin seems almost to contradict himself, when he writes that " the most important point to make about the putative dualism of practical reason is that deliberation of a sufficiently global scope is not conducted in terms of ‘prudence’, ‘self-interest’, or ‘flourishing’ on the one side and ‘morality’ on the other. It is conducted in terms of strength of practical reasons." If this is true, how can he hold that there is a level in which we deliberate "by appeal to any one substantive prudential value but to the notion of prudential value itself" ? I think that Scanlon's argues his view much more convincingly than Griffin.