Chapter 11 · Macroeconomic objectives II: Economic growth, sustainable level of debt
Short-run economic growth: increasing AD
Show how increasing aggregate demand raises actual real GDP when spare capacity exists. Distinguish short-run growth from greater potential output.
The economic idea
Economic growth is an increase in real output over time. Actual economic growth is an increase in the real GDP currently produced, whereas potential economic growth is an increase in the maximum sustainable output the economy can produce.
Short-run growth can occur when consumption, investment, government expenditure or net exports increase aggregate demand while spare capacity exists. Firms respond to stronger sales by raising production and employment, so cyclical unemployment tends to fall.
The movement along SRAS normally raises the average price level as well as output. The division between real growth and inflation depends on spare capacity, the slope of SRAS, the multiplier, import leakage and expectations.
Debt-financed government expenditure may support actual growth during a downturn. Public debt is the accumulated stock of government borrowing, while a budget deficit is an annual flow. Whether debt is sustainable depends on debt-service costs, the growth of nominal GDP, future primary balances, currency denomination and market confidence—not on the AD–AS diagram alone.
Reading the progression AD₁ → AD₂ → AD₃
“Price level” is on the vertical axis and “Real GDP” is on the horizontal axis.
“AD₁”, “AD₂” and “AD₃” show successive levels of planned expenditure. “SRAS” is unchanged, so productive capacity has not been shown to increase.
“E₁”, “E₂” and “E₃” identify the equilibrium price level and actual output at each stage.
Starting point: E₁
“AD₁” intersects “SRAS” at “E₁”, establishing the initial price level “Pl₁” and real GDP “Y₁”.
Intermediate expansion: E₂
The move from “AD₁” to “AD₂” raises planned expenditure. Firms respond to falling inventories by moving along “SRAS” toward “E₂”, where output is “Y₂”.
Current outcome: E₃
The aggregate-demand curves progress rightward from “AD₁” through “AD₂” to “AD₃”. Actual real GDP rises from “Y₁” to “Y₃”, while the price level rises from “Pl₁” to “Pl₃”. The graph therefore shows short-run actual growth using more of the existing productive capacity.
Is higher output evidence of higher productive capacity?
Not on its own. Stronger spending can raise actual real GDP by bringing idle labour and equipment into use. The economy produces more with the capacity it already has.
To claim potential growth, identify an increase in the quantity or quality of resources, or better technology. To claim a particular growth rate, you also need output values and a time period; the distance between labelled equilibria is not a percentage growth rate.
From autonomous expenditure to actual growth
A rise in autonomous consumption, investment, government expenditure or net exports shifts AD from “AD₁” toward “AD₂” and “AD₃”.
At the previous price level, planned expenditure exceeds current output, inventories fall and firms increase production.
Higher production raises derived demand for labour and reduces cyclical unemployment as the economy moves along “SRAS”.
Common mistakes to avoid
- The movement from “Y₁” to “Y₃” is actual growth; “SRAS” has not shifted, so the graph does not establish potential growth.
- A rise in nominal GDP caused only by higher prices is not real economic growth.
- Demand-led growth is not automatically sustainable when the economy has little spare capacity.
- The graph does not display a budget deficit, public debt or the debt-to-GDP ratio; those require additional fiscal evidence.
How to draw this diagram
- Title the diagram “Short-run economic growth: increasing AD”. Label the horizontal axis “Real GDP” and the vertical axis “Price level”.
- Draw AD₁ first and label it clearly.
- Draw AD₂ next and label it clearly.
- Draw AD₃ next and label it clearly.
- Draw SRAS next and label it clearly.
- Mark each relevant intersection and distinguish the initial, market and socially optimum or policy outcomes where applicable.
- Project important intersections to the axes with dashed guide lines and label the outcomes.
- Check that every symbol used in the explanation appears on the diagram and add arrows showing the direction of change.
Assumptions and limitations
- The diagram shows comparative equilibria rather than the time required for output to adjust.
- It does not identify which component of aggregate demand changed or how large the multiplier is.
- Potential output may change through investment, scarring or hysteresis even though it is held fixed here.
- Real GDP growth does not reveal per-capita living standards, income distribution, unpaid work or environmental costs.
- No fiscal variables are plotted, so the model cannot establish whether public debt is sustainable.