part of teaching economics is teaching economic reasoning. Our discipline is built around deductive logic. Once we teach students a pattern of logic we want and expect them to apply it to new circumstances.when they apply the logic of a simple demand curve or a simple supply curve to the aggregate demand or aggregate supply curve the logic does not fit. we believe that the best way to teach the reasoning embodied tn the aggregate demand and aggregate supply curves without creating confusion for student is to build up to those topics carefully.