Quantity Theory of Money

The quantity theory of money is a theory that variations in price relate to variations in the money supply. The most common version, sometimes called the "neo-quantity theory" or Fisherian theory, suggests there a mechanical and fixed proportional relationship between changes in the money supply and the general price level. This popular, albeit controversial, formulation of the quantity theory of money is based upon an equation by American economist Irving Fisher.

The Fisher equation is calculated as:

Where: M represents the money supply.

V represents the velocity of money.

P represents the average price level.

T represents the volume of transactions in the economy.

Generally speaking, the quantity theory of money assumes that increases in the quantity of money tend to create inflation, and vice versa. For example, if the Federal Reserve or European Central Bank (ECB) doubled the supply of money in the economy, the long-run prices in the economy would tend to increase dramatically.

Economists disagree about how quickly and how proportionately prices adjust after a change in the quantity of money. The classical treatment in most economic textbooks is based on the Fisher Equation, but competing theories exist.

The Fisher model has many strengths, including simplicity and applicability to mathematical models. However, it uses some spurious assumptions to generate its simplicity, including an insistence on proportional increases in the money supply, variable independence and emphasis on price stability.

Monetarist economics, usually associated with the Chicago school of economics, advocate the Fisher model. From their interpretation, monetarists often support a stable or consistent increase in money supply. While not all economists accept this view, more economists accept the monetarist claim that changes in the money supply cannot affect the real level of economic output in the long run.

Keynesians more or less use the same framework as monetarists, with few exceptions. John Maynard Keynes rejected the direct relationship between M and P, as he felt it ignored the role of interest rates. Keynes also argued the process of money circulation is complicated and not direct, so individual prices for specific markets adapt differently to changes in the money supply. Keynes believed inflationary policies could help stimulate aggregate demand and boost short-term output to help an economy achieve full employment.

The most serious challenge to Fisher came from Swedish economist Knut Wicksell, whose theories developed in continental Europe, while Fisher's grew in the United States and Great Britain. Wicksell, along with later writers such as Ludwig von Mises and Joseph Schumpeter, agreed that increases in the quantity of money led to higher prices. However, an artificial stimulation of the money supply through the banking system would distort prices unevenly, particularly in the capital goods sectors. This, in turn, shifts real wealth unevenly and could even cause business cycles.

The dynamic Wicksellian and Keynesian models stand in contrast to the static Fisherian model. Unlike the monetarists, adherents to the later models don't advocate a stable price level in monetary policy.