Logic and the Law: Philosophical Foundations, Deontics, and Defeasible Reasoning

This chapter is a light-weighted overview of significant contributions to legal logic insofar as they involve deontic reasoning and related methods. A special emphasis is given to defeasible reasoning, which has been the major topic for legal reasoning in the last decades. The chapter is divided into three parts and the layout is as follows. Part 1 provides an introductory outline. In particular, we briefly recall an issue that was discussed in the context of deontic logic and that has been as well a hot research theme in legal reasoning, i.e., the very possibility of the use of logic in the law. Part 2 reconstructs the contribution of the literature about some classic topics or methods in deontic logic as relevant for the law: normative positions, the concept of permission, contrary-to-duty reasoning, input/output logic, algebras for normative systems, norm change, defeasibility in law. Part 3 is the largest one and offers, from our previous work, a unifying formal framework, based on Defeasible Logic, re-addressing some of the topics that we have already discussed in Part 2: legal hierarchies and dynamics, institutional agency and normative positions, and deontic aspects of legal interpretation.