Murray N. Rothbard
Money in a Free Society
3. Indirect Exchange
But man discovered, in the process of trial and error, the route that permits a greatly-expanding economy: indirect exchange. Under indirect exchange, you sell your product not for a good which you need directly, but for another good which you then, in turn, sell for the good you want. At first glance, this seems like a clumsy and round-about operation. But it is actually the marvelous instrument that permits civilization to develop.
Consider the case of A, the farmer, who wants to buy the shoes made by B. Since B doesn't want his eggs, he finds what B does want--let's say butter. A then exchanges his eggs for C's butter, and sells the butter to B for shoes. He first buys the butter no: because he wants it directly, but because it will permit him to get his shoes. Similarly, Smith, a plow-owner, will sell his plow for one commodity which he can more readily divide and sell--say, butter--and will then exchange parts of the butter for eggs, bread, clothes, etc. In both cases, the superiority of butter--the reason there is extra demand for it beyond simple consumption--is its greater marketability. If one good is more marketable than anothe--if everyone is confident that it will be more readily sold--then it will come into greater demand because it will be used as a medium of exchange. It will be the medium through which one specialist can exchange his product for the goods of other specialists.
Now just as in nature there is a great variety of skills and resources, so there is a variety in the marketability of goods. Some goods are more widely demanded than others, some are more divisible into smaller units without loss of value, some more durable over long periods of time, some more transportable over large distances. All of these advantages make for greater marketability. It is clear that in every society, the most marketable goods will be gradually selected as the media for exchange. As they are more and more selected as media, the demand for them increases because of this use, and so they become even more marketable. The result is a reinforcing spiral: more marketability causes wider use as a medium which causes more marketability, etc. Eventually, one or two commodities are used as general media--in almost all exchanges--and these are called money.
Historically, many different goods have been used as media: tobacco in colonial Virginia, sugar in the West Indies, salt in Abyssinia, cattle in ancient Greece, nails in Scotland, copper in ancient Egypt, and grain, beads, tea, cowrie shells, and fishhooks. Through the centuries, two commodities, gold and silver, have emerged as money in the free competition of the market, and have displaced the other commodities. Both are uniquely marketable, are in great demand as ornaments, and excel in the other necessary qualities. In recent times, silver, being relatively more abundant than gold, has been found more useful for smaller exchanges, while gold is more useful for larger transactions. At any rate, the important thing is that whatever the reason, the free market has found gold and silver to be the most efficient moneys.
This process: the cumulative development of a medium of exchange on the free market--is the only way money can become established. Money cannot originate in any other way, neither by everyone suddenly deciding to create money out of useless material, nor by government calling bits of paper "money." For embedded in the demand for money is knowledge of the money-prices of the immediate past; in contrast to directly-used consumers' or producers' goods, money must have pre-existing prices on which to ground a demand. But the only way this can happen is by beginning with a useful commodity under barter, and then adding demand for a medium for exchange to the previous demand for direct use (e.g., for ornaments, in the case of gold ). Thus, government is powerless to create money for the economy; it can only be developed by the processes of the free market.
A most important truth about money now emerges from our discussion: money is a commodity. Learning this simple lesson is one of the world's most important tasks. So often have people talked about money as something much more or less than this. Money is not an abstract unit of account, divorceable from a concrete good; it is not a useless token only good for exchanging; it is not a "claim on society"; it is not a guarantee of a fixed price level. It is simply a commodity. It differs from other commodities in being demanded mainly as a medium of exchange. But aside from this, it is a commodity--and, like all commodities, it has an existing stock, it faces demands by people to buy and hold it, etc. Like all commodities, its "price"--in terms of other goods--is determined by the interaction of its total supply, or stock, and the total demand by people to buy and hold it. (People "buy" money by selling their goods and services for it, just as they "sell" money when they buy goods and services.)
 On the origin of money, cf. Carl Menger, Principles of Economics (Glencoe, Illinois: Free Press, 1950), pp. 257-71; Ludwig von Mises, Theory of Money and Credit, 3rd Ed. (New Haven Yale University Press, 1951), pp. 97-123.