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In monetary economics, the quantity theory of money (QTM) states that money supply has a direct, proportional relationship with the price level. For example, if the currency in circulation increased, there would be a proportional increase in the price of goods.〔http://www.britannica.com/EBchecked/topic/486147/quantity-theory-of-money〕 The theory was challenged by Keynesian economics,〔Minsky, Hyman P. ''John Maynard Keynes'', McGraw-Hill. 2008. p.2.〕 but updated and reinvigorated by the monetarist school of economics. While mainstream economists agree that the quantity theory holds true in the long run, there is still disagreement about its applicability in the short run. Critics of the theory argue that money velocity is not stable and, in the short-run, prices are sticky, so the direct relationship between money supply and price level does not hold. Alternative theories include the real bills doctrine and the more recent fiscal theory of the price level. == Origins and development of the quantity theory == The quantity theory descends from Nicolaus Copernicus,〔Nicolaus Copernicus (1517), memorandum on monetary policy.〕 followers of the School of Salamanca, Jean Bodin,〔Jean Bodin, ''Responses aux paradoxes du sieur de Malestroict'' (1568).〕 Henry Thornton, and various others who noted the increase in prices following the import of gold and silver, used in the coinage of money, from the New World. The “equation of exchange” relating the supply of money to the value of money transactions was stated by John Stuart Mill〔John Stuart Mill (1848), ''Principles of Political Economy''.〕 who expanded on the ideas of David Hume.〔David Hume (1748), “Of Interest,” "Of Interest" in ''Essays Moral and Political''.〕 The quantity theory was developed by Simon Newcomb,〔Simon Newcomb (1885), ''Principles of Political Economy''.〕 Alfred de Foville,〔Alfred de Foville (1907), ''La Monnaie''.〕 Irving Fisher,〔Irving Fisher (1911), ''The Purchasing Power of Money'',〕 and Ludwig von Mises〔von Mises, Ludwig Heinrich; ''Theorie des Geldes und der Umlaufsmittel'' Henry Thornton introduced the idea of a central bank after the financial panic of 1793, although, the concept of a modern central bank wasn't given much importance until Keynes published "A Tract on Monetary Reform" in 1923. In 1802, Thornton published "An Enquiry into the Nature and Effects of the Paper Credit of Great Britain" in which he gave an account of his theory regarding the central bank's ability to control price level. According to his theory, the central bank could control the currency in circulation through book keeping. This control could allow the central bank to gain a command of the money supply of the country. This ultimately would lead to the central bank's ability to control the price level. His introduction of the central bank's ability to influence the price level was a major contribution to the development of the quantity theory of money.〔Hetzel, Robert L. "Henry Thornton: Seminal Monetary Theorist and Father of the Modern Central Bank." HENRY THORNTON: SEMINAL MONETARY THEORIST AND FATHER OF THE MODERN CENTRAL BANK (n.d.): 1. July-Aug. 1987. Web.〕 Karl Marx modified it by arguing that the Labor Theory of Value requires that prices, under equilibrium conditions, are determined by socially necessary labor time needed to produce the commodity and that quantity of money was a function of the quantity of commodities, the prices of commodities, and the velocity.〔(Capital Vol I, Chapter 3, B. The Currency of Money ), as well ''A Contribution to the Critique of Political Economy'' Chapter II, 3 "Money"〕 Marx did not reject the basic concept of the Quantity Theory of Money, but rejected the notion that each of the four elements were equal, and instead argued that the quantity of commodities and the price of commodities are the determinative elements and that the volume of money follows from them. He argued... John Maynard Keynes, like Marx, accepted the theory in general and wrote... Also like Marx he believed that the theory was misrepresented. Where Marx argues that the amount of money in circulation is determined by the quantity of goods times the prices of goods Keynes argued the amount of money was determined by the purchasing power or aggregate demand. He wrote In the Tract on Monetary Reform (1924),〔(Tract on Monetary Reform, London, United Kingdom: Macmillan, 1924 )〕 Keynes developed his own quantity equation: n = p(k + rk'),where n is the number of "currency notes or other forms of cash in circulation with the public", p is "the index number of the cost of living", and r is "the proportion of the bank's potential liabilities (k') held in the form of cash." Keynes also assumes "...the public,(k') including the business world, finds it convenient to keep the equivalent of k consumption in cash and of a further available k' at their banks against cheques..." So long as k, k', and r do not change, changes in n cause proportional changes in p.〔"Keynes' Theory of Money and His Attack on the Classical Model", L. E. Johnson, R. Ley, & T. Cate (International Advances in Economic Research, November 2001) ()〕 Keynes however notes... Keynes thus accepts the Quantity Theory as accurate over the long-term but not over the short term. Keynes remarks that contrary to contemporaneous thinking, velocity and output were not stable but highly variable and as such, the quantity of money was of little importance in driving prices.〔“The Counter-Revolution in Monetary Theory”, Milton Friedman (IEA Occasional Paper, no. 33 Institute of Economic Affairs. First published by the Institute of Economic Affairs, London, 1970.) ()〕 The theory was influentially restated by Milton Friedman in response to the work of John Maynard Keynes and Keynesianism.〔Milton Friedman (1956), “The Quantity Theory of Money: A Restatement” in ''Studies in the Quantity Theory of Money'', edited by M. Friedman. Reprinted in M. Friedman ''The Optimum Quantity of Money'' (2005), pp. (51 )-(67. ) 〕 Friedman understood that Keynes was like Friedman, a "quantity theorist" and that Keynes Revolution "was from, as it were, within the governing body", i.e. consistent with previous Quantity Theory.〔 Friedman notes the similarities between his views and those of Keynes when he wrote... Friedman notes that Keynes shifted the focus away from the quantity of money (Fisher's M and Keynes' n) and put the focus on price and output. Friedman writes... The Monetarist counter-position was that contrary to Keynes, velocity was not a passive function of the quantity of money but it can be an independent variable. Friedman wrote: Thus while Marx, Keynes, and Friedman all accepted the Quantity Theory, they each placed different emphasis as to which variable was the driver in changing prices. Marx emphasized production, Keynes income and demand, and Friedman the quantity of money. Academic discussion remains over the degree to which different figures developed the theory.〔 For instance, Bieda argues that Copernicus's observation amounts to a statement of the theory, while other economic historians date the discovery later, to figures such as Jean Bodin, David Hume, and John Stuart Mill.〔 Historically, the main rival of the quantity theory was the real bills doctrine, which says that the issue of money does not raise prices, as long as the new money is issued in exchange for assets of sufficient value.〔Roy Green (1987), “real bills doctrine”, in ''The New Palgrave: A Dictionary of Economics'', v. 4, pp. 101-02.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Quantity theory of money」の詳細全文を読む スポンサード リンク
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