I have posted a significantly revised and expanded version of this paper that first went on-line two years ago.  The abstract of the new version:

Ronald Dworkin describes an approach to how courts should decide cases that he associates with Judge Richard Posner as a "Chicago School of anti-theoretical, no-nonsense jurisprudence." Since Professor Dworkin takes his own view of adjudication to be diametrically opposed to that of the Chicago School, it might seem fair, then, to describe Dworkin's own theory as an instance of pro-theoretical, nonsense jurisprudence. That characterization is not one, needless to say, that Professor Dworkin welcomes. Dworkin describes his preferred approach to jurisprudential questions, to be sure, as theoretical, in opposition to what he calls the practical orientation of the Chicago School. But while there is a real dispute between Dworkin and Posner, it is not one illuminated by the contrast between theory and practice. It is, rather a dispute about the kind of theory that is relevant and illuminating when it comes to law and adjudication. And the fault line marked by this dispute is profound indeed, one that extends far beyond Dworkin and Posner and has a venerable and ancient history that includes Thucydides and Plato, Nietzsche and Kant, Marx and Hegel, up to Geuss and Rawls in the present. I shall describe it, instead, as a dispute between Moralists and Realists, between those whose starting point is a theory of how things (morally) ought to be versus those who begin with a theory of how things really are. The essay endeavors to show that our contemporaries, Ronald Dworkin and Richard Posner, are reenacting a version of the dispute between the paradigmatic philosophical moralist Plato and the paradigmatic historical realist Thucydides. The paper concludes by connecting the Posner-Dworkin dispute with recent "realist" critiques of Rawlsian political philosophy, trying to clarify the grounds for skepticism about the practical relevance of such theorizing.