When the medium of exchange diverges in value from the ultimate standard, as in the case of the American Greenbacks during the period from 1862 to 1879, we have, sometimes, shifting relations among the functions. The Greenbacks were the measure of value most commonly in use. They were legal tender for debts, except where gold was specified in the contract. They were commonly the standard of deferred payments. To a considerable extent, however, gold was used in reserves, and even as a medium of exchange. People _thought_ in both standards. And finally, gold remained an ultimate standard to which the Greenbacks were referred, and by which variations in their value were measured. The terms, "primary standard" (gold) and "secondary standard" (Greenbacks), have been employed to aid in straightening out this confusion.[474] I think, on the whole, that the term, "common measure of values" describes the function which I wish to emphasize more clearly than the term, standard of values, and I shall, in general, employ it for that purpose.[475]
The medium of exchange function grows out of the physical difficulties of barter, rather than out of intellectual needs. The discussion in the preceding chapter of the origin of money has emphasized the nature of the difficulties which a medium of exchange meets. A has an ox, which he wishes to trade for shoes, sugar, and a coat. Neither shoe-maker, tailor nor grocer cares to take the ox, however, and, besides, no one of them could supply A with all three of the things he wishes to get. Moreover, even if A should meet a man who had all three things, he would not care to give up the ox for them, since the ox is worth more than all three. If there be a medium of exchange, however, A may sell his ox to the butcher, and take his pay in that medium, which will be something easily and minutely divisible, buy coat and sugar and shoes, and take the surplus of his medium of exchange home, waiting for another occasion. The medium of exchange function overcomes the difficulties arising from low saleability of many goods, due to limited number of possible buyers, lack of divisibility, etc., etc.
The common measure of values aids greatly in determining the prices, the terms, at which exchanges may be made; the medium of exchange makes possible exchanges which could not be made at all in its absence.