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Walras’ Law is a principle in general equilibrium theory asserting that budget constraints imply that the ''values'' of excess market demands (or, conversely, excess market supplies) must sum to zero. That is: : where is the price of good ''i'' and and are the demand and supply respectively of good ''i''. Walras' Law is named for the economist Léon Walras of the University of Lausanne who formulated the concept in his ''Elements of Pure Economics'' of 1874.〔(【引用サイトリンク】title=Walras' Law )〕 Although the concept was expressed earlier but in a less mathematically rigorous fashion by John Stuart Mill in his ''Essays on Some Unsettled Questions of Political Economy'' (1844), Walras noted the mathematically equivalent proposition that when considering any particular market, if all other markets in an economy are in equilibrium, then that specific market must also be in equilibrium. The term "Walras' Law" was coined by Oskar Lange〔Lange, O. 1942. Say’s law: A restatement and criticism. In Lange, O., F. McIntyre, and T. O. Yntema, eds., ''Studies in Mathematical Economics and Econometrics, in Memory of Henry Schultz'', pages 49–68. University of Chicago Press, Chicago.〕 to distinguish it from Say's Law. Some economic theorists〔Florenzano, M. 1987. On an extension of the Gale–Nikaido–Debreu lemma. ''Economics Letters'' 25(1):51–53.〕 also use the term to refer to the weaker proposition that the total value of excess demand cannot exceed the total values of excess supply. ==Definitions== *A market for a particular commodity is in equilibrium if, at the current prices of all commodities, the quantity of the commodity demanded by potential buyers equals the quantity supplied by potential sellers. For example, suppose the current market price of cherries is $1 per pound. If all cherry farmers summed together are willing to sell a total of 500 pounds of cherries per week at $1 per pound, and if all potential customers summed together are willing to buy 500 pounds of cherries in total per week when faced with a price of $1 per pound, then the market for cherries is in equilibrium because neither shortages nor surpluses of cherries exist. *An economy is in general equilibrium if every market in the economy is in equilibrium. Not only must the market for cherries clear, but so too must all markets for all commodities (apples, automobiles, etc.) and for all resources (labor and economic capital) and for all financial assets, including stocks, bonds, and money. *'Excess demand' refers to a situation in which a market is not in equilibrium at a specific price because the number of units of an item demanded exceeds the quantity of that item supplied at that specific price. Excess demand yields an economic shortage. A negative excess demand is synonymous with an excess supply, in which case there will be an economic surplus of the good or resource. 'Excess demand' may be used more generally to refer to the algebraic value of quantity demanded minus quantity supplied, whether positive or negative. 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「Walras' law」の詳細全文を読む スポンサード リンク
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