Miracles in formal theories of action

摘要

Most work on reasoning about action is based on the implicit assumption that there are no events happening in the world concurrently with the actions that are being carried out. We discuss the possibility of relaxing this assumption and treating it as a default principle—if it is inconsistent with the given facts, then we will admit the possibility of unknown events, “miracles,” that, along with the given actions, contribute to the properties of the new situation. The formalism proposed by one of the authors in the paper, Formal Theories of Action, does not treat “miracles” properly. We discuss a modification of that approach which corrects this problem.