Matthew L. Ginsberg, David E. Smith
In this paper, we propose a solution to McCarthy’s qualification problem  based on the notion of possible worlds [3,6]. We begin by noting that existing formal solutions to qualification seem to us to suffer from serious epistemological and computational difficulties. We present a formalization of action based on the notion of possible worlds, and show that our solution to the qualification problem avoids the difficulties encountered by earlier ones by associating to each action a set of domain constraints that can potentially block it. We also compare the computational resources needed by our approach with those required by other formulations.