wares equalised with A's. Then the proportion will be correct, A:B::C:D; now Reciprocation will be practicable, if it were not, there would have been no dealing.
Now that what connects men in such transactions is Demand, as being some one thing, is shown by the fact that, when either one does not want the other or neither want one another, they do not exchange at all: whereas they do when one wants what the other man has, wine for instance, giving in return corn for exportation.
And further, money is a kind of security to us in respect of exchange at some future time (supposing that one wants nothing now that we shall have it when we do): the theory of money being that whenever one brings it one can receive commodities in exchange: of course this too is liable to depreciation, for its purchasing power is not always the same, but still it is of a more permanent nature than the commodities it represents. And this is the reason why all things should have a price set upon them, because thus there may be exchange at any time, and if exchange then dealing. So money, like a measure, making all things commensurable equalises them: for if there was not exchange there would not have been dealing, nor exchange if there were not equality, nor equality if there were not the capacity of being commensurate: it is impossible that things so greatly different should be really commensurate, but we can approximate sufficiently for all practical purposes in reference to Demand. The common measure must be some one thing, and also from agreement (for which reason it is called νόμισμα), for this makes all things commensurable: in fact, all things are measured by money. Let B represent ten minæ, A a house worth five minæ, or in other words half B, C a bed worth 110 of B: it is clear then how many beds are equal to one house, namely, five.
It is obvious also that exchange was thus conducted before the existence of money: for it makes no difference whether you give for a house five beds or the price of five beds.
