Finally, some one may ask why gold is capable of being replaced
 by tokens that have no value? But, as we have already seen, it is capable
 of being so replaced only in so far as it functions exclusively as coin,
 or as the circulating medium, and as nothing else. Now, money has other
 functions besides this one, and the isolated function of serving as the
 mere circulating medium is not necessarily the only one attached to gold
 coin, although this is the case with those abraded coins that continue
 to circulate. Each piece of money is a mere coin, or means of circulation,
 only so long as it actually circulates. But this is just the case with
 that minimum mass of gold, which is capable of being replaced by paper
 money. That mass remains constantly within the sphere of circulation, continually
 functions as a circulating medium, and exists exclusively for that purpose.
 Its movement therefore represents nothing but the continued alternation
 of the inverse phases of the metamorphosis C—M—C, phases in which commodities
 confront their value-forms, only to disappear again immediately. The independent
 existence of the exchange-value of a commodity is here a transient apparition,
 by means of which the commodity is immediately replaced by another commodity.
 Hence, in this process which continually makes money pass from hand to
 hand, the mere symbolical existence of money suffices. Its functional existence
 absorbs, so to say, its material existence. Being a transient and objective
 reflex of the prices of commodities, it serves only as a symbol of itself,
 and is therefore capable of being replaced by a token. [38]
 One thing is, however, requisite; this token must have an objective
 social validity of its own, and this the paper symbol acquires by its forced
 currency. This compulsory action of the State can take effect only within
 that inner sphere of circulation which is coterminous with the territories
 of the community, but it is also only within that sphere that money completely
 responds to its function of being the circulating medium, or becomes coin.