📚 Keynesian and Monetarist Theoretical Approaches | 凯恩斯主义与货币主义理论方法
Keynesian and monetarist schools of thought have shaped macroeconomic policy debates since the mid‑20th century. While Keynesians focus on the instability of aggregate demand and advocate active fiscal intervention, monetarists emphasise the central role of money supply and argue for rule‑based policies to maintain price stability. This article examines the core theoretical approaches of both camps, their views on inflation, unemployment, policy effectiveness, and the evolving synthesis in modern economics.
凯恩斯主义与货币主义学派自20世纪中叶以来深刻地塑造了宏观经济政策的争论。凯恩斯主义者聚焦于总需求的不稳定性，主张积极的财政干预；而货币主义者则强调货币供给的核心作用，倡导基于规则的政策以维持物价稳定。本文考察两大阵营的核心理论方法、它们对通胀与失业的看法、政策有效性，以及现代经济学中不断演变的综合。
1. The Two Great Schools of Macroeconomics | 宏观经济学的两大流派
Keynesian economics, rooted in the writings of John Maynard Keynes, emerged as a response to the Great Depression and the perceived failure of classical self‑adjustment mechanisms. It places aggregate demand at the heart of output and employment determination in the short run and calls for discretionary demand‑management policies.
凯恩斯主义经济学源于约翰·梅纳德·凯恩斯的著作，它是对大萧条及古典自我调节机制失效的回应。该理论将总需求置于短期产出与就业决定的核心，并呼吁采取相机抉择的需求管理政策。
Monetarism, championed by Milton Friedman and his followers at the Chicago School, reasserted the classical idea that the economy tends towards a natural equilibrium, with money supply being the predominant factor influencing nominal income. Monetarists favour a steady, rule‑governed expansion of the money stock.
货币主义由米尔顿·弗里德曼及其芝加哥学派追随者倡导，重申了古典观点，即经济趋向于自然均衡，而货币供给是影响名义收入的主导因素。货币主义者主张稳定地、按规则扩张货币存量。
2. Keynesian Economics: The Primacy of Aggregate Demand | 凯恩斯主义经济学：总需求至上
In the Keynesian framework, aggregate demand (AD) is inherently volatile because of shifts in business confidence, consumer sentiment, and liquidity preference. A fall in AD can lead to equilibrium below full employment, causing persistent involuntary unemployment. The simple Keynesian cross model illustrates how output adjusts to match planned expenditure, with the multiplier effect amplifying initial changes in autonomous spending.
在凯恩斯主义框架中，总需求（AD）本质上是不稳定的，因为企业信心、消费者情绪和流动性偏好都会发生变化。总需求下降可能导致经济在低于充分就业的水平上达成均衡，从而造成持续的非自愿失业。简单的凯恩斯交叉模型显示了产出如何调整以匹配计划支出，而乘数效应又放大了自主支出的初始变动。
Keynesians argue that, in a deep recession, monetary policy may become ineffective due to the liquidity trap. When interest rates approach zero, increases in the money supply are simply hoarded rather than spent. Hence, fiscal policy – government spending and tax cuts – is the primary stabilisation tool. A budget deficit directly injects demand into the circular flow of income.
凯恩斯主义者认为，在深度衰退中，由于流动性陷阱，货币政策可能失效。当利率接近零时，货币供给的增加只会被储存起来，而非被支出。因此，财政政策——政府支出与减税——成为主要的稳定工具。预算赤字直接向收入循环流注入需求。
The Keynesian aggregate supply curve is often drawn as upward‑sloping in the short run but relatively flat when there is substantial spare capacity. This means that increases in AD result more in higher real output than in higher prices, especially in a slump.
凯恩斯主义的总供给曲线在短期通常向上倾斜，但在存在大量闲置产能时相对平坦。这意味着，总需求的增加更多地带来实际产出的提高，而非价格上涨，尤其在经济低迷时期。
3. Monetarism: The Central Role of Money Supply | 货币主义：货币供给的核心作用
Monetarism is built upon the Quantity Theory of Money. The classic equation of exchange states: M × V = P × Y, where M is the money supply, V is the velocity of circulation, P is the price level, and Y is real output (or transactions). Monetarists argue that V is stable and predictable, so changes in M lead directly to changes in nominal spending (P × Y).
货币主义建立在货币数量论之上。经典的交易方程式为：M × V = P × Y，其中M是货币供给，V是货币流通速度，P是物价水平，Y是实际产出（或交易量）。货币主义者认为V是稳定且可预测的，因此M的变动会直接导致名义支出（P × Y）的变动。
In the short run, an increase in the money supply may boost real output and employment, but over time the economy moves to its natural rate. The long‑run outcome is purely inflationary, a principle called monetary neutrality. This implies that the long‑run aggregate supply (LRAS) curve is vertical at the full‑employment level of output.
在短期，货币供给的增加可能会刺激实际产出和就业，但随着时间推移，经济会回归自然率。长期结果纯粹是通货膨胀，这一原理被称为货币中性。这意味着长期总供给曲线（LRAS）在充分就业产出水平上垂直。
Friedman’s famous dictum, ‘Inflation is always and everywhere a monetary phenomenon,’ captures the monetarist conviction that sustained price rises can only occur if the money stock grows faster than real output over time.
弗里德曼的名言“通货膨胀无论何时何地都是一种货币现象”抓住了货币主义者的信念，即只有当货币存量长期增长快于实际产出时，物价的持续上涨才会发生。
4. The Quantity Theory of Money and Velocity | 货币数量论与流通速度
The Quantity Theory is central to monetarist analysis. Keynesians, in contrast, treat velocity as unstable and endogenous – it varies with the speculative demand for money. If people expect low bond prices, they will hoard money, causing V to fall. This undermines a direct relationship between M and P.
货币数量论是货币主义分析的核心。相比之下，凯恩斯主义者认为流通速度是不稳定的和内生的——它随货币的投机性需求而变化。如果人们预期债券价格走低，他们会储存货币，导致V下降。这削弱了M与P之间的直接关联。
Friedman and Anna Schwartz, in their monumental ‘Monetary History of the United States,’ provided empirical evidence that velocity moves slowly and predictably and that major economic contractions, including the Great Depression, were linked to prior reductions in the money supply. This offered a powerful counter‑narrative to the Keynesian spending‑driven explanation.
弗里德曼与安娜·施瓦茨在其里程碑式的《美国货币史》中提供了实证证据，表明流通速度变化缓慢且可预测，包括大萧条在内的重大经济收缩都与先前的货币供给缩减相关。这为反对凯恩斯主义支出驱动型解释提供了有力的叙事。
5. The Phillips Curve and Inflation‑Unemployment Trade‑off | 菲利普斯曲线与通胀‑失业权衡
The original Phillips curve suggested an inverse and stable relationship between wage inflation (and later price inflation) and unemployment. Keynesians incorporated this into policy models, arguing that governments could select a combination of inflation and unemployment along a stable trade‑off.
最初的菲利普斯曲线显示工资膨胀（后来的价格膨胀）与失业之间存在稳定的反向关系。凯恩斯主义者将此纳入政策模型，认为政府可以沿着一条稳定的权衡曲线选择通胀与失业的组合。
Monetarists, most notably Friedman and Edmund Phelps, challenged this view by introducing the expectations‑augmented Phillips curve. Only unexpected inflation can temporarily lower unemployment below its natural rate. Once workers and firms adjust their expectations, unemployment returns to the natural rate, but inflation is permanently higher. Thus, the long‑run Phillips curve is vertical.
货币主义者，最著名的是弗里德曼和埃德蒙·费尔普斯，通过引入附加预期的菲利普斯曲线挑战了这一观点。只有未预期的通胀才能暂时将失业压至自然失业率以下。一旦工人与企业调整了预期，失业便会回到自然率，但通胀水平却永久抬高了。因此，长期菲利普斯曲线是垂直的。
6. Expectations: Adaptive versus Rational | 预期：适应性预期与理性预期
Monetarists initially built their models on adaptive expectations, where agents form expectations of future inflation based on past inflation rates. This produces temporary deviations from the natural rate but ensures that monetary expansion eventually becomes fully anticipated and ineffective at altering real variables.
货币主义者最初将模型建立在适应性预期之上，即经济主体根据过去通货膨胀率形成对未来通胀的预期。这会导致暂时偏离自然率，但货币扩张最终会被完全预期到，从而无法改变实际变量。
New classical economists, inspired by Robert Lucas, went further with rational expectations. Under this assumption, individuals use all available information and anticipate the effects of systematic policy. Consequently, only random, unforecastable policy shocks can influence output – a concept known as the policy ineffectiveness proposition.
新古典经济学家受到罗伯特·卢卡斯的启发，运用理性预期更进一步。根据这一假设，个人会利用所有可获得的信息，并预见到系统性政策的效果。因此，只有随机的、不可预测的政策冲击才能影响产出——这一概念称为政策无效性命题。
7. Crowding Out and Fiscal Policy Effectiveness | 挤出效应与财政政策有效性
A key point of contention is the extent of crowding out. Keynesians acknowledge that an increase in government borrowing may push up interest rates, but they argue that in a slump, with private investment largely insensitive to interest costs and plenty of idle resources, crowding out is minimal.
一个关键的争论点是挤出效应的程度。凯恩斯主义者承认政府借款增加可能会抬高利率，但他们主张，在经济低迷时期，私人投资对利息成本基本不敏感，且存在大量闲置资源，此时挤出效应微乎其微。
Monetarists uphold the full crowding‑out view: a bond‑financed fiscal expansion merely replaces private spending. Higher government borrowing raises the demand for loanable funds, driving up interest rates and discouraging private investment. The rise in public sector demand is offset by a fall in the private sector, leaving aggregate demand unchanged in the long run.
货币主义者坚持完全挤出观点：通过发行债券融资的财政扩张只是替代了私人支出。政府借款增加推高了对可贷资金的需求，抬升了利率，抑制了私人投资。政府部门的支出增加被私人部门的下降所抵消，长期内总需求维持不变。
8. Policy Rules versus Discretion | 政策规则与相机抉择
The debate over rules versus discretion encapsulates the normative differences between the two schools. Keynesians favour discretionary policy because they believe the economy is subject to unpredictable shocks that require timely and tailored responses by fiscal authorities.
规则与相机抉择之争概括了两个学派之间的规范性差异。凯恩斯主义者偏好相机抉择，因为他们认为经济会遭受不可预测的冲击，需要财政当局及时且有针对性的应对。
Monetarists argue that discretionary policy often suffers from long and variable time lags – recognition, decision, and implementation lags – so that by the time a stimulus takes effect, the economy may already be recovering. Worse, politicians may manipulate policy for electoral gain, creating a political business cycle. A monetary growth rule, whereby the central bank increases the money supply by a fixed percentage each year in line with the long‑run growth rate of real output, would provide greater stability.
货币主义者认为，相机抉择政策常常面临漫长而多变的时滞——认识时滞、决策时滞和执行时滞——以至于当刺激措施生效时，经济可能已经自行复苏。更糟的是，政客可能为了选举利益而操纵政策，制造政治性经济周期。货币增长规则，即央行每年按照实际产出的长期增长率固定百分比扩大货币供给，将带来更大的稳定性。
9. The Natural Rate of Unemployment and Supply‑side Policies | 自然失业率与供给侧政策
The natural rate of unemployment (sometimes referred to as the non‑accelerating inflation rate of unemployment, NAIRU) is central to monetarist analysis. It is the rate determined by structural and frictional factors such as labour market rigidities, the efficiency of job matching, and the generosity of welfare benefits. Attempts to push unemployment below this rate through demand expansion only fuel accelerating inflation.
自然失业率（有时被称为非加速通货膨胀失业率，NAIRU）是货币主义分析的核心。它是由结构性和摩擦性因素决定的失业率，例如劳动力市场刚性、职位匹配效率以及福利慷慨程度。试图通过需求扩张将失业率压至该水平以下只会引发加速上升的通货膨胀。
From this insight emerges the monetarist emphasis on supply‑side policies: reducing trade‑union power, cutting unemployment benefits, improving labour‑market flexibility, and reforming education and training. These measures shift the LRAS curve rightward, lowering the natural rate and enabling non‑inflationary output growth.
由此衍生出货币主义者对供给侧政策的重视：削弱工会力量、削减失业救济、提高劳动力市场灵活性以及改革教育与培训。这些措施使LRAS曲线向右移动，降低自然失业率，并实现无通胀的产出增长。
10. Long‑run Neutrality of Money and the Vertical AS Curve | 长期货币中性与垂直的总供给曲线
Both monetarists and new classical economists argue that money is neutral in the long run: changes in the nominal money stock have no lasting effect on real GDP, employment, or the real interest rate. The long‑run aggregate supply curve is vertical at full‑employment output (Yf). Any increase in AD, regardless of its source, merely raises the price level from P1 to P2.
货币主义者和新古典经济学家都认为，长期内货币是中性的：名义货币存量的变动对实际GDP、就业或实际利率没有持久影响。长期总供给曲线在充分就业产出（Yf）处垂直。无论来源于什么，总需求的任何增加只会使物价水平从P1升至P2。
Keynesians do not dispute the vertical LRAS as a theoretical long‑run abstraction, but they are sceptical of its short‑run relevance. They emphasise that ‘in the long run we are all dead,’ and that long periods of mass unemployment are socially and politically intolerable. Active intervention remains essential to close the output gap promptly.
凯恩斯主义者并不否认LRAS的垂直性作为一个理论上的长期抽象概念，但他们对其短期相关性持怀疑态度。他们强调“长期而言我们都死了”，长期的大规模失业在社会和政治上是难以承受的。积极干预对于迅速弥合产出缺口仍然至关重要。
11. The Great Inflation and the Monetarist Counter‑revolution | 大通胀与货币主义反革命
The stagflation of the 1970s – simultaneously high inflation and unemployment – posed a formidable challenge to the conventional Keynesian framework, which could not easily explain the coincidence. Monetarists attributed the Great Inflation to excessive expansion of the money supply, exacerbated by the Federal Reserve’s attempt to target low nominal interest rates without adjusting for inflationary expectations.
20世纪70年代的滞胀——高通胀与高失业并存——对传统凯恩斯主义框架构成了严峻挑战，后者难以轻易解释这一并存现象。货币主义者将大通胀归因于货币供给的过度扩张，并因美联储试图盯住低名义利率而未针对通胀预期作出调整而加剧。
This episode gave credibility to the monetarist call for monetary discipline. Many central banks subsequently adopted monetary‑growth targets, and the focus shifted towards controlling inflation through interest‑rate policy (a modern adaptation) and ensuring central bank independence.
这段历史赋予了货币主义者倡导的货币纪律以可信度。许多央行随后采用了货币增长目标，重点转向通过利率政策（现代适应形式）控制通胀，并确保中央银行独立性。
12. Synthesis and Modern Macroeconomics | 综合与现代宏观经济学
Today’s macroeconomics reflects a pragmatic synthesis. Most economists accept that in the long run the LRAS curve is vertical and that sustained inflation is driven by the money supply. However, they also recognise that prices and wages are sticky in the short run, meaning that demand shocks – whether originating from fiscal policy or private sector confidence – can cause significant fluctuations in output and employment. The New Keynesian models incorporate rational expectations and micro‑founded price rigidities, offering a rigorous justification for short‑run policy activism while preserving long‑run monetary neutrality.
今天的宏观经济学反映了一种务实的综合。大多数经济学家承认，长期内LRAS曲线是垂直的，持续通胀由货币供给推动。但他们也认识到，价格与工资在短期内是黏性的，这意味着需求冲击——无论是源于财政政策还是私人部门信心——都可能导致产出与就业的显著波动。新凯恩斯主义模型融合了理性预期和微观基础的价格刚性，为短期政策干预提供了严谨的理据，同时保留长期货币中性。
Monetarist ideas remain embedded in the consensus: central banks today operate with a clear mandate for price stability, often using inflation‑targeting frameworks, and policy is conducted with an eye on the natural rate and supply‑side flexibility. The Keynesian spirit lives on in the acceptance that, in severe downturns, conventional monetary policy may be insufficient and that active fiscal stimulus becomes necessary to revive aggregate demand.
货币主义思想仍深植于共识之中：今天的央行以清晰的物价稳定职责运作，常采用通胀目标制框架，并在执行政策时关注自然率与供给侧灵活性。凯恩斯主义精神则体现在对下述观点的接受上：在严重衰退中，常规货币政策可能不足，必须依靠积极的财政刺激来重振总需求。
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