Defeasible Conditional Obligation in a Two-tiered Preference-based Semantics (Extended Version)

TL;DR

This paper introduces a two-tiered, preference-based semantic framework for modeling defeasible conditional obligations, incorporating nonmonotonic reasoning and dual preference orderings to improve normative reasoning.

Contribution

It extends Hansson-Lewis style semantics with a bi-preferential approach and connects it to I/O logic, enabling withdrawal of obligations with new information.

Findings

Developed a bi-preferential semantic framework for defeasible obligations.

Incorporated nonmonotonic reasoning mechanisms for normative logic.

Established a connection with constrained I/O logic.

Abstract

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deontic logic by incorporating a nonmonotonic reasoning mechanism that enables previously derived obligations to be withdrawn when new, potentially conflicting information comes in.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.