Supply-side economics is better known to some as "Reaganomics", or the "trickle-down" policy espoused by former U.S. president Ronald Reagan. He popularized the controversial idea that greater tax cuts for investors and entrepreneurs provides incentives to save and invest and produce economic benefits that trickle down into the overall economy. In this article, we summarize the basic theory behind supply-side economics.
 
Like most economic theories, supply-side economics tries both to explain macroeconomic phenomena and - based on these explanations - to offer policy prescriptions for stable economic growth. In general, supply-side theory has three pillars: tax policy, regulatory policy and monetary policy.

However, the single idea behind all three pillars is that production (i.e. the "supply" of goods and services) is the most important determinant of economic growth. The supply-side theory is typically held in stark contrast to Keynesian theory, which, among other facets, includes the idea that demand can falter, so if lagging consumer demand drags the economy into recession, the government should intervene with fiscal and monetary stimuli.

This is the single big distinction: a pure Keynesian believes that consumers and their demand for goods and services are key economic drivers, while a supply-sider believes that producers and their willingness to create goods and services set the pace of economic growth.

The Argument That Supply Creates Its Own Demand
In economics we review the supply and demand curves. The left-hand chart below illustrates a simplified macroeconomic equilibrium: aggregate demand and aggregate supply intersect to determine overall output and price levels. (In this example, output may be gross domestic product and the price level may be the Consumer Price Index.) The right-hand chart illustrates the supply-side premise: an increase in supply (i.e. production of goods and services) will increase output and lower prices.

Starting Point

Increase in Supply (Production)

Supply-side actually goes further and claims that demand is largely irrelevant. It says that over-production and under-production are not really sustainable phenomena. Supply-siders argue that when companies temporarily "over-produce", excess inventory will be created, prices will subsequently fall and consumers will increase their purchases to offset the excess supply. As put by the Fountainhead Capital Group, "After all, what would cause consumers and businesses to stop demanding goods and services and force the economy into a recession or a depression? Keynes had no idea, and said as much…." 

This essentially amounts to the belief in a vertical (or almost vertical) supply curve, as shown below on the left-hand chart below. On the right-hand chart, we illustrate the impact of an increase in demand: prices rise but output doesn't change much.

Vertical Supply Curve

An Increase in Demand → Prices Go Up

Under such a dynamic - where the supply is vertical - the only thing that increases output (and therefore economic growth) is an increase in the production of the supply of goods and services. As illustrated below:

Supply-Side Theory Only an Increase in Supply (Production) Raises Output

Three Pillars
The three supply-side pillars follow from this premise. On the question of tax policy, supply-siders argue for lower marginal tax rates. In regard to a lower marginal income tax, supply-siders believe that lower rates will induce workers to prefer work over leisure (at the margin). In regard to lower capital-gains tax rates, they believe that lower rates induce investors to deploy capital productively. At certain rates, a supply-sider would even argue that the government would not lose total tax revenue because lower rates would be more than offset by a higher tax revenue base - due to greater employment and productivity.

Continued...