Why a sudden drop in spending can trigger a permanent economic spiral
In short: During the 1929 Wall Street crash, the private sector faced a devastating loss of output. Without intervention, a cycle of layoffs and reduced consumer spending threatened to lock the economy into a state of permanent, involuntary unemployment. Understanding how to break this downward spiral requires looking at the mechanics of aggregate demand.
Aggregate demand, or domestic final demand, represents the total demand for a country's final goods and services at a specific time. It is the sum of four distinct pillars: consumption by households, planned business investment, government expenditure, and net exports. While it is often theorized as a downward-sloping curve, the Sonnenschein–Mantel–Debreu results suggest that this slope cannot be mathematically derived solely from individual rational behavior. Three pillars of macroeconomics underpin this: the Mundell–Fleming exchange-rate effect, the Keynes interest rate effect, and the Pigou wealth effect.
Price levels and money supply dictate how this curve functions. Under the Keynes effect, a higher price level reduces the real money supply, driving up interest rates and stifling investment in new physical capital. Simultaneously, the Pigou effect suggests that rising prices erode real wealth, which in turn lowers consumption. In a small open economy, the Mundell–Fleming model further extends these relationships by incorporating the interplay between nominal exchange rates, interest rates, and output.
The impact of demand shifts depends heavily on an economy's proximity to its potential output. When an economy has significant unemployed resources, an increase in aggregate demand—driven by higher government spending or tax decreases—tends to boost real production and employment. However, as the economy approaches its potential GDP, these same shifts result in more intense price increases rather than output gains. In modern industrial economies, the focus often shifts to managing these shifts to avoid the disastrous deflation seen in places like Japan, or the inflationary pressures that occur when output exceeds potential levels.
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- Summary by Intellect · source: Aggregate demand
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