In this paper I argue that to explain and resolve some kinds of disagreement we need to go beyond what logic alone can provide. In particular, following Perelman, I argue that we need to consider how arguments are ascribed different strengths by different audiences, according to how accepting these arguments promotes values favoured by the audience to which they are addressed. I show how we can extend the standard framework for modelling argumentation systems to allow different audiences to be represented. (...) I also show how this formalism can explain how some disputes can be resolved while in others the parties can only agree to differ. I illustrate this by consideration of a legal example. Finally, I make some suggestions as to where these values come from, and how they can be used to explain differences across jurisdictions, and changes in views over time. (shrink)

The author revisits H. L. A. Hart's theory of positive law and argues for a major qualification to the thesis of the separation of law and morality based on a concept of systemic legitimacy derived from the social theory of Jurgen Habermas. He argues that standards for assessing the degree of systemic legitimacy in modern legal systems can develop through reflective exercise of “critical legality,” a concept coined to parallel Hart's “critical morality,” and an expanded understanding of the “external” and (...) “internal” perspectives on legal systems. Following Habermas, he argues that modern positive law must retain systemic legitimacy. After suggesting criteria for measuring systemic legitimacy, the author concludes that the concept provides a useful approach to contemporary problems of “lawless” regimes and “law's imperialism.”. (shrink)