Whether money is shells or rocks or gold or paper, it has three primary functions in any economy: as a medium of exchange, as a unit of account, and as a store of value. Of the three functions, its function as a medium of exchange is what distinguishes money from other assets such as stocks, bonds, and houses.
In almost all market transactions in our economy, money in the form of currency or checks is a medium of exchange; it is used to pay for goods and services. The use of money as a medium of exchange promotes economic efficiency by minimizing the time spent in exchanging goods and services. To see why, let's look at a barter economy, one without money, in which goods and services are exchanged directly for other goods and services.
Take the case of Ellen the Economics Professor, who can do just one thing well: give brilliant economics lectures. In a barter economy, if Ellen wants to eat, she must find a farmer who not only produces the food she likes but also wants to learn economics. As you might expect, this search will be difficult and time-consuming, and Ellen might spend more time looking for such an economics-hungry farmer than she will teaching. It is even possible that she will have to quit lecturing and go into farming herself. Even so, she may still starve to death.
The time spent trying to exchange goods or services is called a transaction cost. In a barter economy, transaction costs are high because people have to satisfy a "double coincidence of wants"—they have to find someone who has a good or service they want and who also wants the good or service they have to offer.
Let's see what happens if we introduce money into Ellen the Economics Professors world. Ellen can teach anyone who is willing to pay money to hear her lecture. She can then go to any farmer (or his representative at the supermarket) and buy the food she needs with the money she has been paid. The problem of the double coincidence of wants is avoided, and Ellen saves a lot of time, which she may spend doing what she does best: teaching.
As this example shows, money promotes economic efficiency by eliminating much of the time spent exchanging goods and services. It also promotes efficiency by allowing people to specialize in what they do best. Money is therefore essential in an economy: It is a lubricant that allows the economy to run more smoothly by lowering transaction costs, thereby encouraging specialization and the division of labor.
The need for money is so strong that almost every society beyond the most primitive invents it. For a commodity to function effectively as money, it has to meet several criteria: (1) It must be easily standardized, making it simple to ascertain its value; (2) it must be widely accepted; (3) it must be divisible, so that it is easy to "make change"; (4) it must be easy to carry; and (5) it must not deteriorate quickly. Forms of money that have satisfied these criteria have taken many unusual forms throughout human history, ranging from wampum (strings of beads) used by Native Americans, to tobacco and whiskey, used by the early American colonists, to cigarettes, used in prisoner-of-war camps during World War II.1 The diversity of forms of money that have been developed over the years is as much a testament to the inventiveness of the human race as the development of tools and language.
Unit of Account The second role of money is to provide a unit of account; that is, it is used to measure value in the economy. We measure the value of goods and services in terms of money, just as we measure weight in terms of pounds or distance in terms of miles. To see why this function is important, let's look again at a barter economy where money does not perform this function. If the economy has only three goods—say, peaches, economics lectures, and movies—then we need to know only three prices to tell us how to exchange one for another: the price of peaches in terms of economics lectures (that is, how many economics lectures you have to pay for a peach), the price of peaches in terms of movies, and the price of economics lectures in terms of movies. If there were ten goods, we would need to know 45 prices in order to exchange one good for another; with 100 goods, we would need 4,950 prices; and with 1,000 goods, 499,500 prices.2
Imagine how hard it would be in a barter economy to shop at a supermarket with 1,000 different items on its shelves, having to decide whether chicken or fish is a better buy if the price of a pound of chicken were quoted as 4 pounds of butter and the price of a pound of fish as 8 pounds of tomatoes. To make it possible to compare
1An extremely entertaining article on the development of money in a prisoner-of-war camp during World War II is R. A. Radford, "The Economic Organization of a P.O.W Camp," Economica 12 (November 1945): 189-201.
2The formula for telling us the number of prices we need when we have N goods is the same formula that tells us the number of pairs when there are N items. It is
In the case of ten goods, for example, we would need
prices, the tag on each item would have to list up to 999 different prices, and the time spent reading them would result in very high transaction costs.
The solution to the problem is to introduce money into the economy and have all prices quoted in terms of units of that money, enabling us to quote the price of economics lectures, peaches, and movies in terms of, say, dollars. If there were only three goods in the economy, this would not be a great advantage over the barter system, because we would still need three prices to conduct transactions. But for ten goods we now need only ten prices; for 100 goods, 100 prices; and so on. At the 1,000-good supermarket, there are now only 1,000 prices to look at, not 499,500!
We can see that using money as a unit of account reduces transaction costs in an economy by reducing the number of prices that need to be considered. The benefits of this function of money grow as the economy becomes more complex.
Store of Value Money also functions as a store of value; it is a repository of purchasing power over time. A store of value is used to save purchasing power from the time income is received until the time it is spent. This function of money is useful, because most of us do not want to spend our income immediately upon receiving it, but rather prefer to wait until we have the time or the desire to shop.
Money is not unique as a store of value; any asset—whether money, stocks, bonds, land, houses, art, or jewelry—can be used to store wealth. Many such assets have advantages over money as a store of value: They often pay the owner a higher interest rate than money, experience price appreciation, and deliver services such as providing a roof over one's head. If these assets are a more desirable store of value than money, why do people hold money at all?
The answer to this question relates to the important economic concept of liquidity, the relative ease and speed with which an asset can be converted into a medium of exchange. Liquidity is highly desirable. Money is the most liquid asset of all because it is the medium of exchange; it does not have to be converted into anything else in order to make purchases. Other assets involve transaction costs when they are converted into money. When you sell your house, for example, you have to pay a brokerage commission (usually 5% to 7% of the sales price), and if you need cash immediately to pay some pressing bills, you might have to settle for a lower price in order to sell the house quickly. Because money is the most liquid asset, people are willing to hold it even if it is not the most attractive store of value.
How good a store of value money is depends on the price level, because its value is fixed in terms of the price level. A doubling of all prices, for example, means that the value of money has dropped by half; conversely, a halving of all prices means that the value of money has doubled. During inflation, when the price level is increasing rapidly, money loses value rapidly, and people will be more reluctant to hold their wealth in this form. This is especially true during periods of extreme inflation, known as hyperinflation, in which the inflation rate exceeds 50% per month.
Hyperinflation occurred in Germany after World War I, with inflation rates sometimes exceeding 1,000% per month. By the end of the hyperinflation in 1923, the price level had risen to more than 30 billion times what it had been just two years before. The quantity of money needed to purchase even the most basic items became excessive. There are stories, for example, that near the end of the hyperinflation, a wheelbarrow of cash would be required to pay for a loaf of bread. Money was losing its value so rapidly that workers were paid and given time off several times during the day to spend their wages before the money became worthless. No one wanted to hold on to money, and so the use of money to carry out transactions declined and barter became more and more dominant. Transaction costs skyrocketed, and as we would expect, output in the economy fell sharply.
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