Macroeconomics
Aggregate Demand
Total demand for goods and services in economy — C + I + G + NX
Aggregate demand (AD) is the total demand for all goods and services in an economy at given price level. Components: C (consumption), I (investment), G (government spending), NX (net exports = exports - imports). AD = C + I + G + NX. Curve slopes downward: lower price level → more aggregate demand. Reasons: wealth effect (real wealth higher), interest rate effect (rates fall), exchange rate effect (exports rise). Shifts: changes in C, I, G, or NX. Foundation of macroeconomic analysis. Combined with aggregate supply: explains output, inflation.
- DefinitionTotal demand for goods/services at given price level
- ComponentsC + I + G + NX
- SlopeDownward (price up, AD down)
- Reasons for slopeWealth effect, interest rate effect, exchange rate effect
- ShiftsChanges in any component
- FoundationCombined with AS, basic macro model
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Why AD matters
- Macroeconomic analysis. Foundation framework.
- Recessions. Often demand shocks.
- Inflation. Excess demand pulls inflation.
- Public policy. Stimulus or restraint.
- Business cycles. Demand fluctuations.
- International economics. Trade balance.
- Education. Foundational macro.
Common misconceptions
- Same as demand for one good. Aggregate (all goods).
- Just consumption. Includes I, G, NX.
- Always desirable. Excess demand causes inflation.
- Government always grows. Can shrink.
- Easy to predict. Many components, expectations.
- Equals supply automatically. Disequilibrium possible.
Frequently asked questions
What's aggregate demand?
Total demand for all goods and services in economy. Sum of consumer spending (C), business investment (I), government spending (G), and net exports (NX). At any price level. Different from individual demand (specific good). Macroeconomic concept. Key in understanding inflation, recession, growth.
Why does the curve slope downward?
Three effects make people demand more at lower price levels. (1) Wealth effect: lower prices → real value of money rises → people richer → consume more. (2) Interest rate effect: lower prices → less money needed for transactions → more for lending → lower interest → more investment. (3) Exchange rate effect: lower domestic prices → exports more competitive → net exports rise.
What shifts AD?
Changes in components. Consumption (C): wealth, taxes, expectations, consumer confidence. Investment (I): interest rates, business confidence, technology. Government (G): policy decisions. Net exports (NX): exchange rates, foreign incomes, trade policies. Each shift: AD curve moves left (decrease) or right (increase). Affects output, prices.
What's the consumption function?
How consumption changes with income. Y = C(income) + I + G + NX. Keynes: consumption depends on disposable income, marginal propensity to consume (MPC). MPC: how much extra spending per extra dollar of income (~0.7 typical). Multiplier: 1/(1-MPC). Foundation of Keynesian macro.
What's investment?
Business spending on capital goods, residential housing, business inventories. Plus: government investment in infrastructure. Volatile component. Sensitive to interest rates (high rates discourage investment). Drives long-term productivity. Different from financial investment (buying stocks, etc.). Pure macro concept.
What about expectations?
Expectations affect AD. Optimistic: spend more now. Pessimistic: save more. Expected inflation: spend now (avoid future higher prices). Expected interest rates: borrowing decisions. Expected income: savings/spending. Self-fulfilling: expecting downturn can cause downturn (less spending → less hiring → less spending).
How does it interact with aggregate supply?
Together: determine equilibrium output and price level. Short-run: AS may slope upward; AD shifts cause output and price changes. Long-run: AS vertical (potential output); AD shifts affect only prices. Recessions: leftward AD shift. Recoveries: rightward shift. Stagflation: combined supply problems and demand issues.