Causality and the Qualification Problem

In formal theories for reasoning about actions, the qualification problem denotes the problem to account for the many conditions which, albeit being unlikely to occur, may prevent the successful execution of an action. By a simple counter-example in the spirit of the well-known Yale Shooting scenario, we show that the common straightforward approach of globally minimizing such abnormal disqualifications is inadequate as it lacks an appropriate notion of causality. To overcome this difficulty, we propose to incorporate causality by treating the proposition that an action is qualified as a fluent which is initially assumed away by default but otherwise potentially indirectly affected by the execution of actions. Our formal account of the qualification problem includes the proliferation of explanations for surprising disqualifications and also accommodates so-called miraculous disqualifications. We moreover sketch a version of the fluent calculus which involves default rules to address abnormal disqualifications of actions, and which is provably correct wrt. our formal characterization of the qualification problem. In L. C. Aiello and J. Doyle and S. Shapiro, editors, Proc. of the International Conference on Principles of Knowledge Representation and Reasoning, pages 51–62, Cambridge, MA, 1996. Morgan Kaufmann