We began this chapter by discussing two models of aggregate supply, each of which focuses on a different reason that, in the short run, output rises above its natural level when the price level rises above the level that people had expected. Both models explain why the short-run aggregate supply curve is upward sloping, and both yield a short-run tradeoff between inflation and unemployment. A convenient way to express and analyze that tradeoff is with the Phillips curve equation, according to which inflation depends on expected inflation, cyclical unemployment, and supply shocks.

Keep in mind that not all economists endorse all the ideas discussed here. There is widespread disagreement, for instance, about the practical importance of rational expectations and the relevance of hysteresis. If you find it difficult to fit all the pieces together, you are not alone. The study of aggregate supply remains one of the most unsettled—and therefore one of the most exciting—research areas in macroeconomics.