Speaker: Kam Sing Leung
Date and Time: Thursday July 7, 2005 @ 1:30pm
Place: ASB 9705

Makinson and van der Torre's Deontic Logics

The traditional approach in deontic logic has been the postulation of a possible world semantics with respect to which a certain axiomatic system is shown to be both sound and complete. However this approach has been criticized for being inadequate to capture the nuances of our normative reasoning (such as normative conflicts, defeasible norms, and contrary-to-duty obligations). We need some new ways to do deontic logic, some have claimed. In this presentation, I will discuss one of the new breeds of deontic logic -- Makinson and van der Torre's input/output logics (2000, 2001). Basically their idea is to treat a normative code (a set of conditional norms) as a generator through which input (a set of propositions stipulating a particular situation) is transformed into output (another set of propositions describing the desired outcomes). By defining various operations and imposing constraints on the generating sets, Makinson and van der Torre come up with different logics, some of which are shown closely related to the default logics of Poole and of Reiter. After examining their input/output logics, we will discuss how this family of logics handle the problems of conflicting and defeasible norms, and contrary-to-duty obligations. It is hoped that, at the end of our discussion, we will be in a better position to judge if there is indeed a new way of doing deontic logic and, if so, where it would lead us to.