In his treatise on the _Revenues of Athens_, Xenophon shows some appreciation of the theory of money. He appears to take for granted that money must have intrinsic value. At least, he understands that silver is a commodity whose value is affected by its use as such, as well as by its employment for currency.[448] He also apprehends the value of a silver currency for international commerce.[449] His naïvely enthusiastic argument for the indefinite increase of the stock of silver, however, is suggestive of the mercantile fallacy, which identified money with wealth.[450] But perhaps he is merely using for practical purposes of argument the fact that the Athenians were accustomed to look upon silver as the metal for fixed and constant value.[451] In any event, he sees that the increase of silver must be attended by a corresponding increase in business activity, if its value is not to depreciate,[452] and he cannot be accused of the error of the mercantilists, that a country is impoverished by the export of money.[453] He must also have understood clearly the importance of stability of value in a currency, since he deems it necessary to show that the increased output of silver will not decrease its value, and that silver is the least changeable of the monetary metals.[454] Despite his enthusiasm for his thesis, which causes him to exaggerate the stability of silver, he does not fail to grasp the direct effect of supply and demand upon it,[455] just as upon gold[456] and other commodities.[457] He shows also some understanding of the quantitative theory of the relation between gold and silver.[458] It need hardly be added that, in strong contrast to Plato, his attitude toward the precious metals, especially silver, is very favorable.[459] EXCHANGE