Xenophon insists strongly on utility or serviceableness as a necessary quality of property (χρήματα, κτήματα). By this, however, he means primarily, not potential utility in the object, but ability of the owner to use rightly.[381] Even exchangeability does not insure value in anything, unless the seller can use to advantage that which he receives in return.[382] This idea of value is true enough from the ethical standpoint, and should not be left out of account, as is being recognized by modern economists. But to attempt to build a theory of economic value on such a basis, as Ruskin does,[383] would result in hopeless confusion. Value is not merely an individual and moral, but also a social and economic, fact. A hint of exchange value is given in the implied classification of goods as usable or salable.[384] But there is no discrimination between useful things in the economic and uneconomic sense. In the _Revenues_, on the other hand, when free from Socratic influence, Xenophon makes a positive contribution to the theory of value. He observes that the exchange value of goods varies with supply and demand, and that this law is, in a sense, self-regulative by the fact that workmen tend to enter other fields of activity whenever any industry becomes unprofitable through an oversupply of its products.[385] WEALTH The double standpoint of Xenophon is well illustrated in his doctrine of wealth. On the one hand, he values it highly, and tries to deduce practical rules for its increase and enjoyment.[386] On the other hand, like Socrates and Plato, he makes derogatory comparisons between economic and spiritual wealth.[387] As in the case of value, he offers no clear definition of economic wealth (κτῆσις). It is defined indiscriminately as “whatever is useful to life,” and “useful” is “everything that anyone knows how to use.”[388] But, as seen above, this is a purely subjective notion, and is only one element in economic wealth.[389] He also defines it (χρήματα) as “the excess of goods over needs,” making it a merely relative term:[390] but here again the thought is ethical rather than economic, an attempt to teach the somewhat ascetic principle that a man’s riches are measured by the paucity of his wants.[391] The hostile or indifferent attitude to wealth is also assumed in the comparison of it with so-called mental wealth and wisdom[392] and in the implication that it involves many cares.[393] The idea so prominent in Plato, however, that the acquisition or expenditure of great wealth is not consistent with justice, is not emphasized by Xenophon. He calls that man happiest who has best succeeded in just acquisition, and who uses his wealth in the best manner.[394] PRODUCTION