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

Abstract:

Addressing a specific concern raised by Horty, this study introduces a two-tiered, preference-based semantic framework designed to model defeasible conditional obligations. Building upon Hansson-Lewis style preference semantics for dyadic deontic logic, the proposed approach integrates a nonmonotonic reasoning mechanism. This mechanism allows for the withdrawal of previously established obligations when new, potentially conflicting information emerges.

The framework is characterized as bi-preferential, utilizing two distinct orderings on worlds—specifically, idealities and normalities—to resolve limitations found in prior models. Each of these orderings employs a separate ranking method. At the nonmonotonic layer, the paper examines several postulates, including antecedent strengthening, inclusion, and the principle of no-drowning. Furthermore, the study establishes a link with constrained input/output (I/O) logic, a well-established standard for normative reasoning that relies on a different methodological foundation.

Source: arXiv Generated at: 2026-06-02 00:00:00 UTC