Formalizing Counterfactual and Nondeterministic Actions in First Order Logic

This short paper outlines some aspects of a method of axiomatizing actions and their effects in standard first-order logic. The method is closely related to other methods using nonmonotonic logics, but the use of first-order logic permits remarkable simplicity. In particular, there is a single, explicit, fixed, and intuitively meaningful frame axiom. Moreover, complex types of inference are possible, including counterfactual reasoning and reasoning about nondeterministic actions.