The Origin and Use of Money

The commerce, besides which any nation can carry on by means of a river, cannot be very considerable. It is always in the power of the nations who possess that other territory, to obstruct communication between the upper country and the sea. One man we shall suppose has more of a certain commodity than he himself has occasion for, while another has less. But if this latter should chance to have nothing that the former stands in need of, no exchange can be made between them. He cannot be their merchant, nor they his customers, and they are all of them thus mutually less serviceable to one another.