Luca Redondi gave several talks at the LuxLogAI workshop in Luxembourg:
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Moral Principles in ASPIC+: A Formal Analysis of Competing Views (joint work with Aleks Knoks)
In many normative theories, we find general ethical principles that are defeasibly applied to particular contexts to detach deontic verdicts. Meta-ethicists argue for different ways to make sense of their defeasibility. One option is to regard them as “contributory”: they specify what counts as a reason for (or against) an action but may be outweighed. Alternatively, one may conceive principles as “hedged”, meaning that they allow for exceptions. Finally, one can hold that principles are both contributory and hedged. We characterize these accounts of principles formally within ASPIC+. The formalization reveals a further distinction, overlooked by the informal literature, between views on principles that satisfy reinstatement and views that do not. We establish correspondences between any pair of models of principles, thus proving that they are all equally expressive. This suggests that the meta-ethical debate over which model is to be preferred should focus on other criteria instead of expressivity. We explore the differences between the models using the notion of (contrastive) deontic explanation: while all models agree on what should (or should not) be the case, they diverge on why it should be.
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On Tipping Scales: a Two-Level Semantics for Balancing Constitutional Rights (joint work with Blaž Istenič Urh and Réka Markovich)
An influential view in legal theory (mostly associated with Robert Alexy) sees balancing of constitutional rights (principles) as reducible to the balancing of case-specific reasons. This means that the strengths of reasons for some legal effects applying or not are compared and if the reasons associated with some legal outcome prevail, its effects are to hold. To model this balancing for the case where reasons are independent, we present the semantics of a novel preference- and truthmaker-based conditional logic. It distinguishes two kinds of statements expressing that a particular combination of case-specific circumstances favors a particular outcome: (1) strong support, which is taken to represent the balancing justified by established case law or by constraints from a higher court, and (2) weak support, which represents the balancing done by the court itself (challenged more easily). In addition, strengths of reasons can be compared. We also relate the formalism to Horty’s reason model for precedential reasoning.
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Mechanizing Implicit Disagreement in Abstract Argumentation with LogiKEy (joint work with Luca Pasetto)