Aggregate Demand and Aggregate Supply

This chapter introduces the Aggregate Demand/Aggregate Supply model of macroeconomics. Read the introduction and Section 1 to learn about Aggregate Demand and the three effects (weath, interest rate, and international trade) that cause the downward slope. Recall the difference between quantity demanded and demand - the same logic applies to Aggregate Demand. Identify the variables that change (shift) the Aggregate Demand curve. Read this chapter and attempt the "Try It" exercises. You will revisit certain sections of the chapter later in this unit.

Start Up: The Great Warning

The first warning came from the Harvard Economic Society, an association of Harvard economics professors, early in 1929. The society predicted in its weekly newsletter that the seven-year-old expansion was coming to an end. Recession was ahead. Almost no one took the warning seriously. The economy, fueled by soaring investment, had experienced stunning growth. The 1920s had seen the emergence of many entirely new industries – automobiles, public power, home appliances, synthetic fabrics, radio, and motion pictures. The decade seemed to have acquired a momentum all its own. Prosperity was not about to end, no matter what a few economists might say.

Summer came, and no recession was apparent. The Harvard economists withdrew their forecast. As it turned out, they lost their nerve too soon. Indeed, industrial production had already begun to fall. The worst downturn in our history, the Great Depression, had begun.

The collapse was swift. The stock market crashed in October 1929. Real GDP plunged nearly 10% by 1930. By the time the economy hit bottom in 1933, real GDP had fallen 30%, unemployment had increased from 3.2% in 1929 to 25% in 1933, and prices, measured by the implicit price deflator, had plunged 23% from their 1929 level. The depression held the economy in its cruel grip for more than a decade; it was not until World War II that full employment was restored.

In this chapter we go beyond explanations of the main macroeconomic variables to introduce a model of macroeconomic activity that we can use to analyze problems such as fluctuations in gross domestic product (real GDP), the price level, and employment: the model of aggregate demand and aggregate supply. We will use this model throughout our exploration of macroeconomics. In this chapter we will present the broad outlines of the model; greater detail, more examples, and more thorough explanations will follow in subsequent chapters.

We will examine the concepts of the aggregate demand curve and the short- and long-run aggregate supply curves. We will identify conditions under which an economy achieves an equilibrium level of real GDP that is consistent with full employment of labor. Potential output is the level of output an economy can achieve when labor is employed at its natural level. Potential output is also called the natural level of real GDP. When an economy fails to produce at its potential, there may be actions that the government or the central bank can take to push the economy toward it, and in this chapter we will begin to consider the pros and cons of doing so.

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