## 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.

### Recessionary and Inflationary Gaps and Long-Run Macroeconomic Equilibrium

#### Recessionary and Inflationary Gaps

At any time, real GDP and the price level are determined by the intersection of the aggregate demand and short-run aggregate supply curves. If employment is below the natural level of employment, real GDP will be below potential. The aggregate demand and short-run aggregate supply curves will intersect to the left of the long-run aggregate supply curve.

Suppose an economy's natural level of employment is Le, shown in Panel (a) of Figure 7.10 "A Recessionary Gap". This level of employment is achieved at a real wage of ωe. Suppose, however, that the initial real wage ω1 exceeds this equilibrium value. Employment at L1 falls short of the natural level. A lower level of employment produces a lower level of output; the aggregate demand and short-run aggregate supply curves, AD and SRAS, intersect to the left of the long-run aggregate supply curve LRAS in Panel (b). The gap between the level of real GDP and potential output, when real GDP is less than potential, is called a recessionary gap.

Figure 7.10 A Recessionary Gap

If employment is below the natural level, as shown in Panel (a), then output must be below potential. Panel (b) shows the recessionary gap YPY1, which occurs when the aggregate demand curve AD and the short-run aggregate supply curve SRAS intersect to the left of the long-run aggregate supply curve LRAS.

Just as employment can fall short of its natural level, it can also exceed it. If employment is greater than its natural level, real GDP will also be greater than its potential level. Figure 7.11 "An Inflationary Gap" shows an economy with a natural level of employment of Le in Panel (a) and potential output of YP in Panel (b). If the real wage ω1 is less than the equilibrium real wage ωe, then employment L1 will exceed the natural level. As a result, real GDP, Y1, exceeds potential. The gap between the level of real GDP and potential output, when real GDP is greater than potential, is called an inflationary gap. In Panel (b), the inflationary gap equals Y1YP.

Figure 7.11 An Inflationary Gap

Panel (a) shows that if employment is above the natural level, then output must be above potential. The inflationary gap, shown in Panel (b), equals Y1YP. The aggregate demand curve AD and the short-run aggregate supply curve SRAS intersect to the right of the long-run aggregate supply curve LRAS.