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

arXiv: https://arxiv.org/abs/2604.26977 · HTML: https://mlsanity.com/paper/2604.26977/

## Key facts

- No citing papers in the map yet (data through 14 Oct 2026).
- Builds on 4 of its 69 references that are in the map.
- First posted on arXiv 28 Apr 2026.

## Builds on (most cited first, 4 of 4)

- [An ASP approach for reasoning in a concept-aware multipreferential lightweight DL](https://mlsanity.com/paper/2006.04387/) (2020)
- [Normative Conditional Reasoning as a Fragment of HOL](https://mlsanity.com/paper/2308.10686/) (2023)
- [Streamlining Input/Output Logics with Sequent Calculi](https://mlsanity.com/paper/2306.09496/) (2023)
- [Dyadic obligations: proofs and countermodels via hypersequents](https://mlsanity.com/paper/2406.09088/) (2024)

## Abstract (arXiv)

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deontic logic by incorporating a nonmonotonic reasoning mechanism that enables previously derived obligations to be withdrawn when new, potentially conflicting information comes in.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