On Moral Reason

I. In Jeffrie G. Murphy's article "Marxism and Retribution", he accuses Rawls of illegitimately presupposing an unargued for and substantive view about what it is rational for one to do, in setting out his account of justice. This presupposition, then, in part, illegitimately determines the outcome of his theory. More specifically, he argues that it is the presupposition of a (merely) historically contingent form of reason. What does this accusation actually amount to? I take it that this accusation is primarily targeted at Rawls' argument for his principles of justice from the original position. 


II. Rawls' original position is a thought experiment that is supposed to bring out our most considered judgements about what justice is, and how we ought to design society. The SEP (because I am not trying to do Rawls' exegesis) describes it as follows: