Murray N. Rothbard
Money in a Free Society
4. Benefits of Money
The emergence of money was a great boon to the human race. Without money--without a general medium of exchange--there could be no real specialization, no advancement of the economy above a bare, primitive level. With money, the problems of indivisibility and "coincidence of wants" that plagued the barter society all vanish. Now, Jones can hire laborers and pay them in... money. Smith can sell his plow in exchange for units of... money. The money-commodity is divisible into small units, and it is generally acceptable by all. And so all goods and services are sold for money, and then money is used to buy other goods and services that people desire. Because of money, an elaborate "structure of production" can be formed, with land, labor services, and capital goods cooperating to advance production at each stage and receiving payment in money.
The establishment of money conveys another great benefit. Since all exchanges are made in money, all the exchange-ratios are expressed in money, and so people can now compare the market worth of each good to that of every other good. If a TV set exchanges for three ounces of gold, and an automobile exchanges for sixty ounces of gold, then everyone can see that one automobile is "worth" twenty TV sets on the market. These exchange-ratios are prices, and the money-commodity serves as a common denominator for all prices. Only the establishment of money-prices on the market allows the development of a civilized economy, for only they permit businessmen to calculate economically. Businessmen can now judge how well they are satisfying consumer demands by seeing how the selling-prices of their products compare with the prices they have to pay productive factors (their "costs"). Since all these prices are expressed in terms of money, the businessmen can determine whether they are making profits or losses. Such calculations guide businessmen, laborers, and landowners in their search for monetary income on the market. Only such calculations can allocate resources to their most productive uses--to those uses that will most satisfy the demands of consumers.
Many textbooks say that money has several functions: a medium of exchange, unit of account, or "measure of values," a "store of value," etc. But it should be clear that all of these functions are simply corollaries of the one great function: the medium of exchange. Because gold is a general medium, it is most marketable, it can be stored to serve as a medium in the future as well as the present, and all prices are expressed in its terms.  Because gold is a commodity medium for all exchanges, it can serve as a unit of account for present, and expected future, prices. It is important to realize that money cannot be an abstract unit of account or claim, except insofar as it serves as a medium of exchange.
 Money does not "measure" prices or values; it is the common denominator for their expression. In short, prices are expressed in money; they are not measured by it.