Two Problems with Reasoning and Acting in Time

Natural language competent embodied cogni tive agents should satisfy two requirements. First, they should act in and reason about a changing world, using reasoning in the ser vice of acting and acting in the service of reasoning. Second, they should be able to communicate their beliefs, and report their past, ongoing, and future actions in natural language. This requires a representation of time using a deictic NOW, that models the compositional semantic properties of the En glish "now". Two problems emerge for an agent that interleaves reasoning and acting in a personal time. The first concerns the repre sentation of plans and reactive rules involving reasoning about "future NOWs". The sec ond emerges when, in the course of reason ing about NOW, the reasoning process itself results in NOW changing. We propose solu tions for the two problems and conclude that: (i) for embodied cognitive agents, time is not just the object of reasoning, but is embedded in the reasoning process itself; and (ii) at any time, there is a partonomy of NOWs repre senting the agent's sense of the current time at different levels of granularity.