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In macroeconomics, aggregate demand (AD) or domestic final demand (DFD) is the total demand for final goods and services in an economy at a given time.〔 〕 It specifies the amounts of goods and services that will be purchased at all possible price levels. This is the demand for the gross domestic product of a country. It is often called effective demand, though at other times this term is distinguished. The aggregate demand curve is plotted with real output on the horizontal axis and the price level on the vertical axis. It is downward sloping as a result of three distinct effects: Pigou's wealth effect, Keynes' interest rate effect and the Mundell-Fleming exchange-rate effect. The Pigou effect states that a higher price level implies lower real wealth and therefore lower consumption spending, giving a lower quantity of goods demanded in the aggregate. The Keynes effect states that a higher price level implies a lower real money supply and therefore higher interest rates resulting from financial market equilibrium, in turn resulting in lower investment spending on new physical capital and hence a lower quantity of goods being demanded in the aggregate. The aggregate demand curve illustrates the relationship between two factors - the quantity of output that is demanded and the aggregate price level. Aggregate demand is expressed contingent upon a fixed level of the nominal money supply. There are many factors that can shift the AD curve. Rightward shifts result from increases in the money supply, in government expenditure, or in autonomous components of investment or consumption spending, or from decreases in taxes. According to the aggregate demand-aggregate supply model, when aggregate demand increases, there is movement up along the aggregate supply curve, giving a higher level of prices.〔Mankiw, N. Gregory, and William M. Scarth. ''Macroeconomics''. Canadian ed., 4th ed. New York: Worth Publishers, 2011. Print.〕 ==History== (詳細はThe General Theory of Employment, Interest and Money'' argued during the Great Depression that the loss of output by the private sector as a result of a systemic shock (the Wall Street Crash of 1929) ought to be filled by government spending. First, he argued that with a lower ‘effective aggregate demand’, or the total amount of spending in the economy (lowered in the Crash), the private sector could subsist on a permanently reduced level of activity and involuntary unemployment, unless there was active intervention. Business lost access to capital, so it had dismissed workers. This meant workers had less to spend as consumers, consumers bought less from business, which because of additionally reduced demand, had found the need to dismiss workers. The downward spiral could only be halted, and rectified by external action. Second, people with higher incomes have a lower marginal propensity to consume their incomes. People with lower incomes are inclined to spend their earnings immediately to buy housing, food, transport and so forth, while people with much higher incomes cannot consume everything. They save instead, which means that the ‘velocity of money’ or the circulation of income through different hands in the economy is decreased. This lowered the rate of growth. Spending should therefore target public works programmes on a large enough scale to speed up growth to its previous levels. 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「aggregate demand」の詳細全文を読む スポンサード リンク
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