---
title: "Cancelling and Overshadowing: Two Types of Defeasibility in Defeasible Deontic Logic"
authors:
  - "Leendert W. N. van der Torre"
  - "Yao-Hua Tan"
doi: ""
url: "https://ijcai.org/proceedings/1995/197"
pdf: "https://ijcai.org/proceedings/1995/0197.pdf"
venue: "Proceedings of the Fourteenth International Joint Conference on Artificial Intelligence"
year: 1995
pages: "1525-1532"
track: "Non-monotonic Reasoning"
keywords:
---

# Cancelling and Overshadowing: Two Types of Defeasibility in Defeasible Deontic Logic

Leendert W. N. van der Torre, Yao-Hua Tan

*Proceedings of the Fourteenth International Joint Conference on Artificial Intelligence*, pages 1525-1532.

## Abstract

In this paper we give a general analysis of dyadic deontic logics that were introduced in the early seventies to formalize deontic reasoning about subideal behavior. Recently it was observed that they are closely related to nonmonotonic logics, theories of diagnosis and decision theories . In particular, we argue that two types of defeasibility must be distinguished in a defeasible deontic logi c: overridden defeasibility that formalizes cancelling of an ob li gation by other conditional obligations and factual defeasibility that formalizes overshadowing of an obligation by a violating fact. We also show that this distinction is essential for an adequate ana lysis of notorious 'paradoxes' of deontic logic such as the Chisholm and Forrester 'Paradoxes'.