Book 5
10
Hence all commodities exchanged must be able to be compared in some way. It is to meet this requirement that men have introduced money; money constitutes in a manner a middle term, for it is a measure of all things, and so of their superior or inferior value, that is to say, how many shoes are equivalent to a house or to a given quantity of food. As therefore a builder is to a shoemaker,It is uncertain whether this merely refers to the difference in value (or perhaps in labor used in production) between the unit products of different trades, or whether it introduces the further conception that different kinds of producers have different social values and deserve different rates of reward. so must such and such a number of shoes be to a house, [or to a given quantity of food]Apparently interpolated from the last sentence.; for without this reciprocal proportion, there can be no exchange and no association; and it cannot be secured unless the commodities in question be equal in a sense.
