Why are close-world assumptions bad for all cases? There might be cases limited to a domain where the computer does not need to know about the world too much. Consider, the language of geometry problems given in high school math books. Surely, to understand that, one doesn't need to have world knowledge, but only ideas about what intersect means, and so on. This way, SHRDLU can be modified to understand geometry problem statements. The same way, it could also work for other domain-limited applications. A general solution might have to go to probabilistic systems, as current research suggests.