Counterfactuals

Counterfactuals are a form of commonsense non-monotonic inference that has been of long-term interest to philosophers. This paper begins by describing some of the impact counterfactuals can be expected to have in artificial intelligence, and by reviewing briefly some of the philosophical conclusions which have been drawn about them. Philosophers have noted that the content of any particular counterfactual is in part context-dependent; we present a formal description of counterfactuals that allows us to encode this context-dependent information clearly in the choice of a sublanguage of the logical language in which we are working. Having made this choice, we show that our description of counterfactuals is formally identical to the accepted possible worlds interpretation due to David Lewis. Finally, we examine the application of our ideas in the domain of automated diagnosis of hardware faults. Additional keywords: operators(mathematics); mathematical logic; semantics; artificial intelligence. (Author).