What Shifts Aggregate Demand

Aggregate demand is the total spending on an economy's goods and services at every possible price level: C + I + G + Nx. The curve slopes down because of the price level's effects on wealth, interest rates, and trade. But a shift of the whole curve happens only when something other than the price level changes spending plans. These shifters sort into the same four buckets as GDP itself: consumer confidence and wealth move C, business expectations and interest rates move I, policy decisions move G, and foreign income or exchange rates move Nx.

Take consumer confidence. If households suddenly feel optimistic about jobs and income, they spend more at every price level, not just at the current one. That extra spending shows up as a rightward shift of the whole AD curve, from AD1 to AD2, because planned expenditure rose for reasons that have nothing to do with prices. The same logic works for a tax cut: it hands households more disposable income, so consumption rises at every price level, and the curve shifts right rather than sliding along itself.

This matters because Unit 3 builds the whole story of the economy around AD meeting short-run and long-run aggregate supply. A rightward AD shift closes a recessionary gap or opens an inflationary one; a leftward shift does the reverse. A trading partner's recession cuts their demand for your exports, shifting your Nx down and your AD curve left, which is exactly the kind of external shock the model is built to track. Fiscal policy, the next piece of the unit, works entirely through these same shifters: government spending and taxes are deliberate attempts to push AD right or left to close those gaps.