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The terms demand and supply are so familiar to the ear of every reader, and their application in single instances so fully understood, that in the slight use which has hitherto been made of them, it has not been thought necessary to interrupt the course of the reasoning by definitions and explanations. These terms, however, though in constant use, are by no means applied with precision. And before we proceed further, it may be advisable to clear this part of the ground as much as possible, that we may be certain of the footing on which we stand. This will appear to be the more necessary, as it must be allowed that of all the principles of political economy, there is none which bears so large a share in the phenomena which come under its consideration as the principle of supply and demand. It has been already stated, that exchangeable value is the relation of one object to some other or others in exchange. And when, by the introduction of a medium of exchange and measure of value, a distinction has been made between buyers and sellers, the demand for any sort of commodities may be defined to be, the will of persons to purchase them, combined with their general means of purchasing; and supply, the quantity of the commodities for sale, combined with the desire to sell them.* It is further evident, that when the use of the precious metals, as a medium of exchange and measure of value, has become general, and during those periods