Preferential Semantics for Causal Systems

In the present work we examine the causal theory of actions put forward by McCain and Turner [McCain and Turner, 1995] for determining ramifications. Our principal aim is to provide a characterisation of this causal theory of actions in terms of a Shoham-like preferential semantics [Shoham, 1988]. This would have a twofold advantage: it would place McCain and Turner's theory in perspective, allowing a comparison with other logics of action; and, it would allow us to glean further insights into the nature of causality underlying their work. We begin by showing that our aim is not attainable by a preferential mechanism alone. At this point we do not abandon preferential semantics altogether but augment it in order to arrive at the desired result. We draw the following moral which is at the heart of our paper: two components -- minimal change under a preferential structure and causality -- are required to provide a concise solution to the frame and ramification problems.