But this quantitative relation can exist only between _homogeneous_ things. The standard, or measure, of values, then, must be like the commodities whose values it is to measure, at least to the extent of having _value_.[114] The second proposition is respecting the medium of exchange. The medium of exchange must also have value, or else be a representative of something which has value. There can be no exchange, in the economic sense--I abstract from disguised benevolences, accidents, and frauds--without a _quid pro quo_, without value balancing value, at least roughly, in the process. Now when it is remembered that the intervention of the medium of exchange, taking the place of barter, really breaks up a single exchange under the barter system into two or more independent exchanges, and that the medium of exchange is actually received in exchange for valuable commodities, it follows clearly that the medium of exchange must either have value itself, or else represent that which has value. These two propositions seem almost too obvious to require the statement, but they contradict the quantity theory, and they are not, on the surface, reconcilable with certain facts in the history of inconvertible paper money. It is necessary, therefore, to state them, and to examine further some of the phenomena which seem to contradict them. If they are true, Nicholson's dodo-bones will perform neither of the primary functions of money. They have no value, _per se_--they cannot, then, measure values; they are neither valuable nor titles to valuable things--they are not _quid pro quo_ in exchange, and will not circulate. I shall not pause long to discuss the doctrine that money needs no value itself, because it is really a sort of title to, or claim on, or representative of, goods in general. The notion, first, would not pass a lawyer's scrutiny. There are no such indefinite legal rights. A system of legally fixed prices, with a socialistic organization of society, would be necessary to give it definiteness--and in such a situation there would be no room for a quantity theory of prices! Economic goods, as distinct from money, are not generally "fungible" to the extent that would make them indifferent objects of legal rights. Besides, whether or not the thing is logically thinkable, it is legally false. Legal factors enter into the economic value of money, as will later be shown, but it is economic, and not legal, value, which makes money circulate. Helfferich has taken the trouble to give the notion of money as a mere title to things in general a somewhat more fundamental analysis, and I would refer the reader who is not satisfied by the foregoing on this point to his discussion.[115]