Supply-Side Policy in the Short and Long Run

A cut in marginal tax rates hits the economy through two separate channels at once. First, lower taxes leave households with more after-tax income, so they spend more right away: that shifts aggregate demand to the right, the same as any tax cut would. Second, a lower marginal rate raises the reward for an extra hour of work, an extra dollar saved, or an extra dollar invested in a business. People keep more of what they earn, so some choose to work more, save more, and firms invest more in capital. That second channel builds up the economy's productive capacity over time, shifting long-run aggregate supply to the right.

When AD and LRAS both move right, output rises on both counts, and the price effects tend to offset: AD alone would push prices up, LRAS alone would push prices down, so the net effect on inflation is smaller and less certain than either shift alone would suggest. This is the supply-side case for tax cuts: more output without the full inflationary cost of a demand-only expansion.

The catch is the size of the behavioral response. A tax cut always costs revenue directly, at the old level of income. It only pays for itself if people work, save, and invest so much more that the larger tax base makes up the lost revenue, and that response is often too small to fully offset the rate cut. The long-run payoff of supply-side policy also connects to the natural rate of unemployment: if incentive effects genuinely raise the capacity to produce, LRAS shifts right and the economy can sustain more output without added inflation, without changing the natural rate itself.