Defeasible Conditional Obligation in a Two-tiered Preference-based Semantics (Extended Version)
For researchers in deontic logic and normative reasoning, this work provides a novel semantic framework that handles defeasibility, but it is incremental as it builds on existing preference semantics and I/O logic.
The paper addresses the problem of modeling defeasible conditional obligations by developing a two-tiered preference-based semantic framework that extends Hansson-Lewis style preference semantics with a nonmonotonic reasoning mechanism. The framework uses two orderings (ideality and normality) to overcome shortcomings in earlier approaches and establishes a connection with constrained input/output logic.
In response to a concern raised by Horty, this paper develops a two-tiered, preference-based semantic framework for modeling defeasible conditional obligations. The paper extends a Hansson-Lewis style preference semantics for dyadic deontic logic by incorporating a nonmonotonic reasoning mechanism that enables previously derived obligations to be withdrawn when new, potentially conflicting information comes in. The account is bi-preferential: two orderings--ideality and normality--on worlds are employed to address shortcomings in earlier approaches, with a separate ranking method for each. At the nonmonotonic layer, a number of postulates are considered, including antecedent strengthening, inclusion and no-drowning. A connection is established with so-called constrained input/output (I/O) logic--an existing standard for normative reasoning based on a different methodology.