ABSTRACT Inspired by legal reasoning, this paper presents a semantics and proof theory of a system for defeasible argumentation. Arguments are expressed in a logic-programming language with both weak and strong negation, conflicts between arguments are decided with the help of priorities on the rules. An important feature of the system is that these priorities are not fixed, but are themselves defeasibly derived as conclusions within the system. Thus debates on the choice between conflicting arguments can also be modelled. The (...) semantics of the system is given with a fixpoint definition, while its proof theory is stated in dialectical style, where a proof takes the form of a dialogue between a proponent and an opponent of an argument: an argument is shown to be justified if the proponent can make the opponent run out of moves in whatever way the opponent attacks. (shrink)

This article examines the role of normative hierarchies in constitutional argumentation. A threefold distinction between formal, material, and axiological hierarchy is employed. The correlative concepts of formal validity, material validity, and applicability are also briefly described. Within this framework, four cases are analysed: Decisions 1146/1988 and 10/2010 of the Italian Constitutional Court, and Kadi I and Opinion 2/2013 of the Court of Justice of the European Union. As a result, it is argued that axiological hierarchies are frequently used to reshape (...) certain fundamental legal arrangements, namely, the hierarchy of sources (Decision 1146/1988 and Kadi), competence clauses (Decision 10/2010), and interpretive methodologies (Opinion 2/13). (shrink)

The author discusses a number of issues in the theory of legal sources. The first topic is whether sources should be conceived of as acts or texts. The alternatives are connected with two competing theories of legal interpretation (viz., the cognitive theory and the sceptical theory), which entail different concepts of legal rules and law‐making. The second topic is whether a “formal” or a “material” criterion of recognition of sources should be preferred. The third section is devoted to the analysis (...) of rules of change. Four theories of rules of change are discussed, and five kinds of such rules are distinguished. The fourth section concerns judicial law‐making, with special reference to the creation of new legal rules by constitutional courts. (shrink)