Proceedings of the Annual Meeting of the Cognitive Science Society

problem solver operating in the real world must adapt its behavior to an unpredictable and changing problem-solving environment. It must react appropriately to changes in the situation, where what is appropriate depends to a large extent on the overall problem-solving context. In order to do this, the reasoner needs to have explicit knowledge about the context it is in. In our approach, the problem-solving context is represented explicitly as a contextual schema. When presented with a problem, the reasoner finds an appropriate contextual schema, then uses it to influence its problem-solving behavior. The reasoner uses the contextual schema to recognize important changes in the problem-solving situation and to respond appropriately to those changes Our approach is implemented in the medic program (Turner, 1988b; Turner, in preparation), medic is medical diagnostic consultant whose domain is puLmonology.