The Supply of Money. Historically, changes in the quantities of certain commodities such as gold affected
the supply of money. That relationship is no longer true.
At least since the early 1970s, central banks have affected the nominal quantities of money in modern economies,
whether intentionally or not, through their policy actions. These policy actions may include buying and selling
government securities, changing reserve requirements, or changing the interest rate at which the central bank
provides reserves to financial intermediaries.
How does the Federal Reserve affect the nominal quantity of money in the United States? The basic principles
are simple, but details can blur them. Suppose that all money in the United States were currency. The Federal
Reserve could buy and sell government securities as it does now in open market operations, using currency
rather than deposits to pay for the securities. When the Federal Reserve bought government securities with currency,
the amount of currency held by the public would increase. When the Federal Reserve sold government
securities and received currency in exchange, the amount of currency held by the public would decrease. These
changes in the amount of currency would be changes in the nominal quantity of money in the economy. While
simplified, this example of such purchases and sales illustrates how the Federal Reserve affects the nominal
quantity of money.4
The Demand for Money. The public’s demand for money is another fundamental part of the relationship
between money growth and inflation. People hold money in order to buy goods and services. As a consequence,
firms’ and households’ demand is for a real quantity of money. If prices increase, then people want to hold more
dollars so that the money will buy the same amount. If M is the nominal quantity of money and P is the price level,
the real quantity of money is M/P. The price level commonly is measured by general price indexes
such as the consumer price index and the gross domestic product deflator. Loosely speaking, the real quantity of
money is the nominal quantity of money adjusted for inflation.
The single most important factor affecting the demand for money is real income. A higher income is associated with more spending, and more spending is facilitated by holding more money. A proportional relationship between the real quantity of money demanded and real income is a convenient form of the dependence of demand for money on income.
This relationship can be written as
M/P = ky,
where y is real income and k is the factor of proportionality.5 The factor of proportionality is not a constant. Most
importantly, changes in the opportunity cost of holding money affect the quantity of money demanded.6 The
opportunity cost of holding money can be summarized by the forgone interest income from holding money instead
of other assets. If the opportunity cost of holding money increases, the demand for money decreases; if the opportunity
cost of holding money decreases, the demand for money increases. Other factors also can affect the demand
for money, such as payments practices and technological innovations in financial intermediation.