Aggregate Supply | 总供给

📚 Aggregate Supply | 总供给

Aggregate supply (AS) measures the total quantity of goods and services that all firms in an economy are willing and able to produce at different price levels over a given period of time. It is a central concept in macroeconomics because it links the price level to national output and helps explain inflation, unemployment, and economic growth.

总供给(AS)衡量一个经济体中所有企业在不同物价水平下在一定时期内愿意并能够生产的商品与服务的总数量。它是宏观经济学的核心概念，因为它将物价水平与国民产出联系起来，有助于解释通货膨胀、失业和经济增长。

In the Cambridge A-Level Economics syllabus, aggregate supply is usually divided into short-run aggregate supply (SRAS) and long-run aggregate supply (LRAS). The short run is the period when at least one factor of production, typically money wages, is fixed, while the long run is the period when all factor prices are fully flexible.

在剑桥 A-Level 经济学考试大纲中，总供给通常分为短期总供给(SRAS)和长期总供给(LRAS)。短期是指至少一种生产要素价格(通常是货币工资)固定的时期，而长期是指所有要素价格都能充分调整的时期。

1. Definition of Aggregate Supply | 总供给的定义

Aggregate supply is not the same as the supply of a single product. It is an economy-wide concept that adds together the planned output of all firms at each possible price level. A rise in the general price level, with input costs unchanged, tends to make production more profitable and therefore encourages firms to expand output.

总供给不同于单个产品的供给。它是一个整体经济概念，将每个可能物价水平下所有企业的计划产出加总在一起。在投入成本不变的情况下，一般物价水平上升往往使生产更有利可图，从而鼓励企业扩大产出。

Aggregate supply can be shown by an AS curve with the general price level on the vertical axis and real GDP or national output on the horizontal axis. The exact shape of the curve depends on whether we are analysing the short run or the long run, and on whether we adopt a classical or Keynesian perspective.

总供给可以用一条 AS 曲线来表示，纵轴为一般物价水平，横轴为实际 GDP 或国民产出。曲线的具体形状取决于我们是在分析短期还是长期，以及采用古典还是凯恩斯学派的视角。

2. Short-Run Aggregate Supply (SRAS) | 短期总供给

The short-run aggregate supply curve shows the relationship between the price level and the quantity of real output firms are willing to produce when money wage rates and other input prices are held constant. In this period, firms can increase output by using existing capital and labour more intensively, but they cannot yet adjust all factor prices fully.

短期总供给曲线表示在货币工资率和其他投入品价格保持不变时，物价水平与企业愿意生产的实际产出数量之间的关系。在这一时期，企业可以通过更密集地使用现有资本和劳动来增加产出，但还无法完全调整所有要素价格。

The SRAS curve is usually drawn upward sloping from left to right. As the price level rises, firms experience higher product prices while their nominal costs remain temporarily fixed, so profit margins widen and they have an incentive to supply more output.

短期总供给曲线通常从左向右向上倾斜。当物价水平上升时，企业面对的产品价格上升，而名义成本暂时固定，因此利润率扩大，企业有动力增加产出。

SRAS: P ↑ → profit margin ↑ → real output supplied ↑

短期总供给：物价水平上升 → 利润率上升 → 实际产出供给增加

3. Why the SRAS Curve Slopes Upward | 短期总供给曲线向上倾斜的原因

The upward slope of the SRAS curve can be explained by sticky input prices. Wages are often fixed by contracts, and many input costs such as rent and energy prices may change slowly. When the general price level increases but input costs do not rise immediately, firms can earn higher profits by selling more output.

短期总供给曲线的向上倾斜可以用投入品价格粘性来解释。工资通常由合同固定，租金和能源价格等许多投入成本变化缓慢。当一般物价水平上升而投入成本没有立即上升时，企业可以通过销售更多产出来获得更高利润。

Another reason is that firms may face rising marginal costs as they push output beyond normal capacity in the short run. Overtime payments, higher maintenance costs and the need to use less efficient machinery all increase unit costs, so higher prices are required to justify higher output.

另一个原因是，当企业在短期内将产出推到正常产能之外时，可能面临边际成本上升。加班费、更高的维护成本以及使用效率较低的机器都会增加单位成本，因此需要更高的价格来支撑更高的产出。

In addition, some input prices may be linked to product prices only with a lag. This means that when the price level rises, the prices of final goods and services increase faster than many input costs, temporarily improving profitability and encouraging extra supply.

此外，一些投入品价格与产品价格的联动存在滞后。这意味着当物价水平上升时，最终商品和服务的价格上涨快于许多投入成本，从而暂时改善盈利能力并鼓励额外供给。

4. Movements Along versus Shifts of SRAS | 短期总供给的沿线移动与曲线移动

A change in the general price level causes a movement along the SRAS curve. When the price level rises, firms expand output and there is an upward movement along the curve; when the price level falls, output contracts and there is a downward movement along the curve.

一般物价水平的变化会引起沿短期总供给曲线的移动。当物价水平上升时，企业扩大产出，沿曲线向上移动；当物价水平下降时，产出收缩，沿曲线向下移动。

A shift of the SRAS curve occurs when a factor other than the price level changes the cost of production or the profitability of supply. For example, an increase in nominal wages, a rise in energy prices, higher indirect taxes or an increase in imported raw material costs shifts the SRAS curve to the left, meaning less is supplied at every price level.

当物价水平以外的因素改变生产成本或供给利润时，短期总供给曲线会发生移动。例如，名义工资上升、能源价格上涨、间接税提高或进口原材料成本增加都会使 SRAS 曲线向左移动，意味着在每一个物价水平上供给量都减少。

Conversely, a fall in unit labour costs, a reduction in commodity prices, lower business taxes or an appreciation of the exchange rate that cheapens imported inputs can shift the SRAS curve to the right. These changes allow firms to supply more output at the same price level.

相反，单位劳动成本下降、大宗商品价格下跌、企业税降低或汇率升值使进口投入品更便宜，都可能使 SRAS 曲线向右移动。这些变化使企业能够在相同物价水平下供给更多产出。

5. Long-Run Aggregate Supply: The Classical View | 长期总供给：古典观点

In the long run, all factor prices, including money wages, are flexible. The classical or monetarist view argues that the long-run aggregate supply curve is vertical at the full employment level of real output, often called potential GDP or Y_f.

在长期中，包括货币工资在内的所有要素价格都能灵活调整。古典学派或货币主义观点认为，长期总供给曲线在充分就业的实际产出水平处垂直，该水平通常称为潜在 GDP 或 Y_f。

The vertical LRAS curve means that real output in the long run is determined by the quantity and quality of factors of production, not by the price level. Changes in aggregate demand can cause short-run fluctuations in output, but in the long run output returns to its potential level.

垂直的长期总供给曲线意味着长期实际产出由生产要素的数量和质量决定，而不受物价水平影响。总需求的变化可以在短期内引起产出波动，但在长期中产出会回到潜在水平。

The classical view assumes that markets clear quickly and that the economy tends to operate at full employment. Any unemployment in the short run is regarded as temporary because wage flexibility will restore equilibrium in the labour market.

古典观点假设市场能够迅速出清，经济往往在充分就业下运行。短期内出现的任何失业都被视为暂时现象，因为工资弹性会使劳动力市场恢复均衡。

LRAS (classical): Y = Y_f = f(L, K, T, N)

长期总供给(古典)：Y = Y_f = f(劳动、资本、技术、自然资源)

6. The Keynesian LRAS Curve | 凯恩斯长期总供给曲线

Keynesian economists argue that the long-run aggregate supply curve is not vertical at all levels of output. Instead, the Keynesian LRAS curve has three sections: a horizontal or perfectly elastic section at low levels of output, an upward-sloping intermediate section, and a vertical section at full capacity.

凯恩斯主义经济学家认为，长期总供给曲线并非在所有产出水平下都垂直。相反，凯恩斯长期总供给曲线分为三段：低产出水平下的水平或完全弹性段、中间向上倾斜段以及充分产能时的垂直段。

The horizontal section reflects an economy with high unemployment and spare capacity. In this situation, output can be increased without putting upward pressure on the price level because idle workers and machines can be brought into production at existing wage and price levels.

水平段反映了存在高失业和闲置产能的经济状况。在这种情况下，可以在不推高物价水平的情况下增加产出，因为闲置的工人和机器可以在现有工资和价格水平下投入生产。

The upward-sloping section occurs as the economy approaches full employment. Firms begin to experience shortages of skilled labour and key inputs, so expanding output requires higher wages and prices. The vertical section shows that once full capacity is reached, further demand growth causes inflation rather than higher real output.

当经济接近充分就业时，出现向上倾斜段。企业开始面临熟练劳动力和关键投入品的短缺，因此扩大产出需要更高的工资和物价。垂直段表明，一旦达到充分产能，进一步的需求增长会导致通货膨胀，而不是更高的实际产出。

This Keynesian view helps explain why an economy can remain in a recession or depression for a long time. Wages and prices may not fall quickly enough to restore full employment, so government intervention may be needed to stimulate aggregate demand.

这一凯恩斯观点有助于解释为什么经济可能长期处于衰退或萧条状态。工资和物价可能无法迅速下降到足以恢复充分就业，因此可能需要政府干预来刺激总需求。

7. Factors That Shift Long-Run Aggregate Supply | 长期总供给移动的因素

The long-run aggregate supply curve shifts when there is a change in the economy’s productive potential. An increase in the quantity or quality of factors of production, or an improvement in technology, shifts LRAS to the right, indicating economic growth.

当经济生产潜力发生变化时，长期总供给曲线就会移动。生产要素数量或质量的提高，或技术的进步，会使 LRAS 向右移动，表明经济增长。

Key factors that shift LRAS to the right include an increase in the labour force, higher productivity, greater capital investment, better education and training, technological progress, discovery of new natural resources, and improvements in infrastructure and institutions.

使 LRAS 向右移动的关键因素包括劳动力增加、生产率提高、资本投资增加、教育和培训改善、技术进步、新自然资源的发现，以及基础设施和制度的改善。

A fall in the productive potential of the economy shifts LRAS to the left. This can be caused by natural disasters, war, a decline in the working-age population, deindustrialisation without replacement, or a fall in the quality of institutions.

经济生产潜力下降会使 LRAS 向左移动。这可能是由自然灾害、战争、劳动年龄人口减少、没有替代产业的去工业化或制度质量下降引起的。

In the Cambridge syllabus, it is important to distinguish between short-run shifts caused by changes in input costs and long-run shifts caused by changes in productive capacity. Supply-side policies aim to shift LRAS to the right.

在剑桥考试大纲中，区分因投入成本变化引起的短期移动与因生产能力变化引起的长期移动非常重要。供给侧政策旨在使 LRAS 向右移动。

8. From Short Run to Long Run: Adjustment Mechanisms | 从短期到长期：调整机制

When an economy is in short-run equilibrium above full employment, inflationary pressure builds. Workers demand higher wages because the cost of living has risen, and firms raise wages to attract scarce labour. Higher wage costs reduce profitability and shift SRAS to the left until output returns to potential GDP at a higher price level.

当经济处于高于充分就业的短期均衡时，通货膨胀压力会累积。由于生活成本上升，工人要求更高的工资，企业也提高工资以吸引稀缺劳动力。更高的工资成本降低了利润率，使 SRAS 向左移动，直到产出回到潜在 GDP，而物价水平更高。

When an economy is in short-run equilibrium below full employment, unemployment is high. In the classical view, downward pressure on wages eventually lowers production costs, shifting SRAS to the right and restoring full employment at a lower price level.

当经济处于低于充分就业的短期均衡时，失业率很高。在古典观点中，工资下降压力最终会降低生产成本，使 SRAS 向右移动，并在较低物价水平下恢复充分就业。

Keynesians, however, argue that wage rates are sticky downwards. Workers resist nominal wage cuts, so the adjustment process can be very slow or incomplete. This is why Keynesians favour active demand management to close a recessionary gap rather than waiting for automatic wage adjustment.

然而，凯恩斯主义者认为工资率具有向下粘性。工人抵制名义工资下降，因此调整过程可能非常缓慢或不完整。这就是为什么凯恩斯主义者倾向于通过积极的需求管理来弥合衰退缺口，而不是等待工资自动调整。

9. Aggregate Supply and Macroeconomic Equilibrium | 总供给与宏观经济均衡

Macroeconomic equilibrium occurs where aggregate demand (AD) equals aggregate supply at a given price level. The nature of this equilibrium depends on whether the economy is operating on the horizontal, upward-sloping or vertical part of the AS curve.

宏观经济均衡发生在某一物价水平下总需求(AD)等于总供给时。这种均衡的性质取决于经济运行在总供给曲线的水平段、向上倾斜段还是垂直段。

In a deep recession, equilibrium may occur on the horizontal section of the Keynesian AS curve. Increases in aggregate demand raise real output and employment without raising the price level, because there is plenty of spare capacity.

在严重衰退中，均衡可能出现在凯恩斯总供给曲线的水平段。总需求增加会提高实际产出和就业，而不会推高物价水平，因为存在大量闲置产能。

As the economy approaches full employment, further increases in aggregate demand cause some inflation and some real growth. At full capacity, the AS curve becomes vertical, and any increase in aggregate demand leads only to a higher price level with no long-run increase in output.

当经济接近充分就业时，总需求进一步增加会导致部分通胀和部分实际增长。在充分产能下，总供给曲线变为垂直，总需求的任何增加只会导致物价水平上升，而长期产出不会增加。

This analysis helps explain the policy trade-off between unemployment and inflation. Supply-side improvements are attractive because they can shift LRAS to the right and allow higher output with lower inflation, avoiding the trade-off altogether.

这一分析有助于解释失业与通货膨胀之间的政策权衡。供给侧改善具有吸引力，因为它们可以使 LRAS 向右移动，从而在较低通胀下实现更高产出，完全避免这种权衡。

10. Supply-Side Policies and Exam Tips | 供给侧政策与考试技巧

Supply-side policies are government measures designed to increase the productive capacity of the economy and shift the LRAS curve to the right. They include improvements in education and training, cuts in income tax to encourage work, reductions in corporation tax to stimulate investment, deregulation, privatisation, and investment in infrastructure.

供给侧政策是政府为提高经济生产能力、使 LRAS 曲线向右移动而采取的措施。它们包括改善教育和培训、降低所得税以鼓励工作、降低公司税以刺激投资、放松管制、私有化以及基础设施投资。

Successful supply-side policies can raise potential output, reduce inflationary pressure, lower unemployment and improve the balance of payments. However, many supply-side measures take time to work and may involve significant public spending in the short run.

成功的供给侧政策可以提高潜在产出、减轻通胀压力、降低失业并改善国际收支。但许多供给侧措施需要时间才能见效，并可能在短期内涉及大量公共支出。

For exam answers, always define aggregate supply clearly, distinguish between SRAS and LRAS, and explain whether a given event causes a movement along or a shift of the curve. Use a diagram where appropriate and link shifts in AS to changes in equilibrium price level and real output.

在考试答题时，务必清晰定义总供给，区分 SRAS 与 LRAS，并说明给定事件是引起曲线沿线移动还是曲线移动。适当使用图示，并将总供给的移动与均衡物价水平和实际产出的变化联系起来。

One common mistake is to confuse SRAS shifts with LRAS shifts. A rise in energy prices shifts SRAS left but does not reduce the economy’s long-run productive potential unless it permanently damages capital or reduces the labour force. Another mistake is to treat the classical and Keynesian LRAS curves as identical, when they reflect different assumptions about wage and price flexibility.

一个常见错误是将 SRAS 移动与 LRAS 移动混淆。能源价格上涨会使 SRAS 向左移动，但除非它永久损害资本或减少劳动力，否则不会降低经济的长期生产潜力。另一个错误是将古典与凯恩斯长期总供给曲线视为相同，而它们反映了关于工资和价格弹性的不同假设。

Feature	Classical LRAS	Keynesian LRAS
Shape	Vertical at Y_f	Horizontal, then upward sloping, then vertical
Wage flexibility	Fully flexible	Sticky downwards
Policy implication	Limited demand management; focus on supply side	Active demand management may be needed

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Aggregate Supply | 总供给