In this paper, we present a scheme for the qualitative representation and simulation of economic theories. We define an associated paradigm of reasoning in accordance with the traditional method of comparative statics. The primitive element of our representation scheme is the simple, demand-supply, market model. More complex economic theories are represented as multiple-market models, with interactions between markets realized by variables of one market model being parameters of another. We define an extension of our single-market simulation process, making it possible to reason about such complex, multiple-market models. We illustrate our notions through consideration of the Keynesian IS-LM macroeconomic model.