The concept of the quantity theory of money (QTM) began in the 16th century. As gold and silver inflows from the Americas into Europe were being minted into coins, there was a resulting rise in inflation. This development led economist Henry Thornton in 1802 to assume that more money equals more inflation and that an increase in money supply does not necessarily mean an increase in economic output. Here we look at the assumptions and calculations underlying the QTM, as well as its relationship to monetarism and ways the theory has been challenged.

### QTM in a Nutshell

The quantity theory of money states that there is a direct relationship between the quantity of money in an economy and the level of prices of goods and services sold. According to QTM, if the amount of money in an economy doubles, price levels also double, causing inflation (the percentage rate at which the level of prices is rising in an economy). The consumer, therefore, pays twice as much for the same amount of the good or service.

Another way to understand this theory is to recognize that money is like any other commodity: increases in its supply decrease marginal value (the buying capacity of one unit of currency). So an increase in money supply causes prices to rise (inflation) as they compensate for the decrease in money's marginal value.

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### The Theory's Calculations

The theory, also known as the Fisher Equation, is most simply expressed as:

﻿\begin{aligned} &MV = PT\\ &\textbf{where:}\\ &M=\text{Money Supply}\\ &V=\text{Velocity of Circulation}\\ &P=\text{Average Price Level}\\ &T=\text{Volume of Transactions of Goods and Services}\\ \end{aligned}﻿

The original theory was considered orthodox among 17th century classical economists and was overhauled by 20th-century economists Irving Fisher, who formulated the above equation, and Milton Friedman. (For more on this important economist, see Free Market Maven: Milton Friedman.)

It is built on the principle of "equation of exchange":

﻿\begin{aligned} &\text{Total Spending} = M \times VC \\ &\textbf{where:}\\ &M=\text{amount of money}\\ &VC=\text{velocity of circulation}\\ \end{aligned}﻿

Thus, if an economy has US$3, and those$3 were spent five times in a month, total spending for the month would be \$15.

### QTM Assumptions

QTM adds assumptions to the logic of the equation of exchange. In its most basic form, the theory assumes that V (velocity of circulation) and T (volume of transactions) are constant in the short term. These assumptions, however, have been criticized, particularly the assumption that V is constant. The arguments point out that the velocity of circulation depends on consumer and business spending impulses, which cannot be constant.

The theory also assumes that the quantity of money, which is determined by outside forces, is the main influence of economic activity in a society. A change in money supply results in changes in price levels and/or a change in supply of goods and services. It is primarily these changes in money stock that cause a change in spending. And the velocity of circulation depends not on the amount of money available or on the current price level but on changes in price levels.

Finally, the number of transactions (T) is determined by labor, capital, natural resources (i.e. the factors of production), knowledge and organization. The theory assumes an economy in equilibrium and at full employment.

Essentially, the theory's assumptions imply that the value of money is determined by the amount of money available in an economy. An increase in money supply results in a decrease in the value of money because an increase in money supply causes a rise in inflation. As inflation rises, the purchasing power, or the value of money, decreases. It therefore will cost more to buy the same quantity of goods or services.

### Money Supply, Inflation, and Monetarism

As QTM says that quantity of money determines the value of money, it forms the cornerstone of monetarism.

Monetarists say that a rapid increase in money supply leads to a rapid increase in inflation. Money growth that surpasses the growth of economic output results in inflation, as there is too much money behind too little production of goods and services. In order to curb inflation, money growth must fall below growth in economic output.

This premise leads to how monetary policy is administered. Monetarists believe that money supply should be kept within an acceptable bandwidth so that levels of inflation can be controlled. Thus, for the near term, most monetarists agree that an increase in money supply can offer a quick-fix boost to a staggering economy in need of increased production. In the long term, however, the effects of monetary policy are still blurry.

Less orthodox monetarists, on the other hand, hold that an expanded money supply will not have any effect on real economic activity (production, employment levels, spending and so forth). But for most monetarists, any anti-inflationary policy will stem from the basic concept that there should be a gradual reduction in the money supply. Monetarists believe that instead of governments continually adjusting economic policies (i.e. government spending and taxes), it is better to let non-inflationary policies (i.e. gradual reduction of money supply) lead an economy to full employment.

### QTM Re-Experienced

John Maynard Keynes challenged the theory in the 1930s, saying that increases in money supply lead to a decrease in the velocity of circulation and that real income, the flow of money to the factors of production, increased. Therefore, velocity could change in response to changes in money supply. It was conceded by many economists after him that Keynes' idea was accurate.

QTM, as it is rooted in monetarism, was very popular in the 1980s among some major economies such as the United States and Great Britain under Ronald Reagan and Margaret Thatcher respectively. At the time, leaders tried to apply the principles of the theory to economies where money growth targets were set. However, as time went on, many accepted that strict adherence to a controlled money supply was not necessarily the cure-all for economic malaise.