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Class 12 Macro Economics Notes · CBSE

Three-Sector Economy

9.6 Three-Sector Economy — how government expenditure (G) shifts the aggregate demand curve and corrects excess/deficient demand. CBSE Class 12 Macroeconomics notes with diagrams.

Last updated: 22 Aug 2026

Notes

Demand in a Three-Sector Economy

In a three-sector economy, the government becomes a key player. Total aggregate demand now includes government expenditure (G), giving us the identity:

AD = C + I + G

The government can influence aggregate demand by adjusting its spending. When the government increases expenditure, the economy moves from an initial demand level to a new, higher level.

Initial AD

AD = C + I

New AD

AD₁ = C + I + G

Government expenditure (G) acts as a direct injection into the circular flow of income, shifting the aggregate demand curve outward.

Correcting Deficient Demand

Deficient demand occurs when aggregate demand falls short of the full-employment level of output, leading to unemployment and a recessionary gap. The government can correct this by increasing its expenditure to boost aggregate demand.

AD + G = AD₁ (C + I + G)

Government spending fills the demand gap

Deficient AD

AD = C + I

Corrected AD

AD₁ = C + I + G

By raising government expenditure, the government directly compensates for the shortfall in private demand, pushing the economy toward full employment.

Correcting Excess Demand

Excess demand occurs when aggregate demand exceeds the full-employment level, causing demand-pull inflation. The government corrects this by reducing its expenditure or raising taxes, thereby lowering aggregate demand.

AD + ΔG = AD₁ (C + I + G + ΔG)

ΔG is negative — government cuts spending

Excess AD

AD = C + I

Corrected AD

AD₁ = C + I + G + ΔG

When ΔG is negative (government reduces expenditure), the net effect is a contraction in aggregate demand, helping cool down an overheated economy.

Key Takeaways

  • In a three-sector economy, AD = C + I + G, where G is government expenditure.
  • Government spending is a direct injection that shifts aggregate demand.
  • Deficient demand is corrected by increasing G to fill the recessionary gap.
  • Excess demand is corrected by decreasing G (ΔG is negative) to reduce inflationary pressure.
  • The government uses fiscal tools to steer the economy toward full-employment equilibrium.