Front Page Titles (by Subject) Separation of Functions. - Money and the Mechanism of Exchange
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Separation of Functions. - William Stanley Jevons, Money and the Mechanism of Exchange 
Money and the Mechanism of Exchange (New York: D. Appleton and Co. 1876).
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Separation of Functions.
It is in the highest degree important that the reader should discriminate carefully and constantly between the four functions which money fulfils, at least in modern societies. We are so accustomed to use the one same substance in all the four different ways, that they tend to become confused together in thought. We come to regard as almost necessary that union of functions which is, at the most, a matter of convenience, and may not always be desirable. We might certainly employ one substance as a medium of exchange, a second as a measure of value, a third as a standard of value, and a fourth as a store of value. In buying and selling we might transfer portions of gold; in expressing and calculating prices we might speak in terms of silver; when we wanted to make long leases we might define the rent in terms of wheat, and when we wished to carry our riches away we might condense it into the form of precious stones. This use of different commodities for each of the functions of money has in fact been partially carried out. In Queen Elizabeth's reign silver was the common measure of value; gold was employed in large payments in quantities depending upon its current value in silver, while corn was required by the Act 18th Elizabeth, c. VI. (1576), to be the standard of value in drawing the leases of certain college lands.
There is evident convenience in selecting, if possible, one single substance which can serve all the functions of money. It will save trouble if we can pay in the same money in which the prices of things are calculated. As few people have the time or patience to investigate closely the history of prices, they will probably assume that the money in which they make all minor and temporary bargains, is also the best standard in which to register debts and contracts extending over many years. A great mass of payments too are invariably fixed by law, such as tolls, fees, and tariffs of charges: many other payments are fixed by custom. Accordingly, even if the medium of exchange varied considerably in value, people would go on making their payments in terms of it, as if there had been no variation, some gaining at the expense of others.
One of our chief tasks in this book will be to consider the various materials which have been employed as money, or have been, or may be, suggested for the purpose. It must be our endeavour, if possible, to discover some substance which will in the highest degree combine the characters requisite for all the different functions of money, but we must bear in mind that a partition of these functions amongst different substances is practicable. We will first proceed to a brief review of the very various ways in which the need of currency has been supplied from the earliest ages, and we will afterwards analyse the physical qualities and circumstances which render the substances employed more or less suited to the purpose to which they were applied. We may thus arrive at some decision as to the exact nature of the commodity which is best adapted to meet our needs in the present day.
Early History of Money
Living in civilized communities, and accustomed to the use of coined metallic money, we learn to identify money with gold and silver; hence spring hurtful and insidious fallacies. It is always useful, therefore, to be reminded of the truth, so well stated by Turgot, that every kind of merchandise has the two properties of measuring value and transferring value. It is entirely a question of degree what commodities will in any given state of society form the most convenient currency, and this truth will be best impressed upon us by a brief consideration of the very numerous things which have at one time or other been employed as money. Though there are many numismatists and many political economists, the natural history of money is almost a virgin subject, upon which I should like to dilate; but the narrow limits of my space forbid me from attempting more than a brief sketch of the many interesting facts which may be collected.