BOOK V

The builder is to receive from the shoemaker of his ware, and to give him of his own: if then there be first proportionate equality, and then the Reciprocation takes place, there will be the just result which we are speaking of: if not, there is not the equal, nor will the connection stand: for there is no reason why the ware of the one may not be better than that of the other, and therefore before the exchange is made they must have been equalised. And this is so also in the other arts: for they would have been destroyed entirely if there were not a correspondence in point of quantity and quality between the producer and the consumer. For, we must remember, no dealing arises between two of the same kind, two physicians, for instance; but say between a physician and agriculturist, or, to state it generally, between those who are different and not equal, but these of course must have been equalised before the exchange can take place.

It is therefore indispensable that all things which can be exchanged should be capable of comparison, and for this purpose money has come in, and comes to be a kind of medium, for it measures all things and so likewise the excess and defect; for instance, how many shoes are equal to a