Intra-Agent Modality and Nonmonotonic Epistemic Logic

It is plausible to think that simulation is perhaps the most important reasoning tool that we have for user modeling. This is behind what we mean when we say that a superlative fisherman can "think like a fish." The fisherman decides where the fish must be by imagining where he would be in this river if he were a fish. Whether or not this idea is sound for fish and fisherman, 1 it certainly applies with a great deal of force to people reasoning about one another 's atti tudes, preferences, emotions, and choices. A friend tells me a story about problems she's been having with her car. She seems quite calm, but I say "You must be upset," reasoning that if this happened to me, I would be upset. I go on, saying "You must realize your mechanic is lying to you" because her description of the problem indicates she knows as much about cars and mechanics as I do, and knowing what she has told me, I would infer that her mechanic is lying. This sort of other-modeling is the reasoning that makes the "golden rule" golden. Wha t would be the moral point of doing unto others as you would have others do unto you if imagining what we ourselves would want were an unreliable way to gauge what others want? In a number of psycholinguistic investigations, Herbert Clark has demonstra ted many ways in which conversation is informed by common ground. The following account of how conversants construct common ground is taken from Clark & Schober [4, pp. 257-158]. (Page numbers from the version in Arenas of Language Use.)