Persistence, Causation and Counterfactuals

Abstract

: We present a novel theory of nonmonotonic temporal reasoning. It is related to approaches based on causation, the main di erence being that in our ap- proach causal relations take a context argument which indicates under what circumstances they should hold. Our theory can handle a very broad class of temporal reasoning problems. It provides an intuitively satisfying account of persistence: a property of the world persists i for every circumstance that would cause it to change, that circumstance is (provably) not the case. But most importantly, our theory clari es the relations between several di erent existing approaches. We identify two central issues which any theory of action, causal or not, somehow must address. The method has been proven correct rel- ative to a `trajectory' semantics de ning a certain class of problems including non-deterministic actions. But it also handles a wide variety of problems that fall outside the scope of these semantics, such as causal chains of events, pre- conditions and rami cations involving several points in time and explanation problems with incomplete knowledge of actions.