  In any case, even if there are suitably substantive principles to which people are committed, and this can be shown, and even if there is a way to establish as well that the principles in question would (if right) actually justify more specific moral judgments, one might understandably worry about the status of the resulting structure. Why not think of it as a castle in the sky, a structure with no appropriate foundation?  After all, the fact that we happen to accept, or are committed to accepting, some principle, seems a long way from showing that the principle is true or right. 