Abstract

This chapter provides an analysis of defeasible legal reasoning as argumentation. It first provides a general account of the idea of defeasibility and introduces the idea of nonmonotonic reasoning. It then focuses on defeasible argumentation, considering how defeasible arguments can be constructed and how they can be defeated by rebutting and undercutting counterarguments. The dialectical interactions of defeasible arguments are further explored by focusing on reinstatement and reasoning about priorities. The idea of legal systems as the basis for argumentation frameworks is then investigated. The rationale for defeasibility in law is discussed, along with the possibility of using different approaches, such as revision or probability, to deal with uncertainty in legal reasoning. Finally, an account is provided of the emergence of theories of defeasibility in philosophy, logic, and legal theory.