9311988 Perlis All reasoning, whether by human or machine, is situated in the physical world and thus subject to time constraints. However, much of the formal study of reasoning agents ignores this, assuming an agent is able to reason forever in a timeless present as if the world had stopped for the agent's benefit. The early work by one of the PIs and his student involved the development of a family of logics--called "step-logics"--for this purpose. More recently the PIs have begun to generalize and modify this work, renaming the formalisms as "active logics". The proposed research would seek to broaden and deepen the existing results of the PIs in time-situated reasoning, specifically in the areas of deadline-coupled planning and acting; language-change; interactive focal points; multi-agent reasoning; and graceful recognition and resolution of contradictions. All five of these areas are ones in which keeping track of changing time during the course of reasoning is useful.
