Keynesianism vs Monetarism: A Complete Comparison – 凯恩斯主义与货币主义的理论对比

一、两大经济学流派的诞生背景 | The Birth of Two Great Schools of Economics

凯恩斯主义与货币主义的对立，是20世纪宏观经济学最核心的争论之一。1929年大萧条爆发后，古典经济学”市场自动出清”的假设被现实击碎，英国经济学家约翰·梅纳德·凯恩斯在1936年出版《就业、利息和货币通论》，提出总需求不足是失业的根源，政府必须通过财政政策主动干预经济。这一思想在战后三十年主导了西方国家的经济政策，被称为”凯恩斯主义共识”。

The rivalry between Keynesianism and Monetarism is one of the most central debates in twentieth-century macroeconomics. After the Great Depression of 1929 shattered the classical assumption that markets automatically clear, the British economist John Maynard Keynes published The General Theory of Employment, Interest and Money in 1936, arguing that deficient aggregate demand is the root cause of unemployment and that governments must actively intervene through fiscal policy. This body of thought dominated Western economic policy for three decades after the war and became known as the “Keynesian consensus”.

然而到了20世纪70年代，西方国家同时出现高通胀与高失业并存的”滞胀”，凯恩斯主义的需求管理政策对此束手无策。以米尔顿·弗里德曼为代表的芝加哥学派货币主义者重新崛起，他们主张通货膨胀归根结底是货币现象，政府应减少干预、让市场机制发挥作用。这场争论不仅是学术理论之争，更深刻影响了各国央行与财政部的实际政策选择，也是CIE A-Level经济学宏观部分的常考主题。

However, in the 1970s the Western world was hit by “stagflation” – high inflation and high unemployment occurring simultaneously – which Keynesian demand-management policies proved powerless to cure. Monetarists of the Chicago School, led by Milton Friedman, rose to prominence, arguing that inflation is ultimately a monetary phenomenon and that governments should intervene less and let market forces work. This debate is not merely academic; it has profoundly shaped the actual policy choices of central banks and finance ministries around the world, and it is a recurring theme in the macroeconomics section of the CIE A-Level Economics examination.

二、核心分歧一：市场能否自动恢复均衡 | Core Disagreement 1: Can Markets Self-Correct?

两大流派最根本的分歧，在于对市场自我修复能力的判断。凯恩斯认为工资和价格具有”刚性”，尤其是名义工资只能上调难以下调，因此当总需求萎缩时，经济会长期停留在低于充分就业的均衡状态，失业将持续存在，市场靠自身力量恢复均衡的过程极其缓慢，甚至可能永远无法完成。

The most fundamental disagreement between the two schools concerns the self-correcting capacity of markets. Keynes argued that wages and prices are “sticky” – nominal wages in particular can rise but are very difficult to cut – so when aggregate demand contracts, the economy can remain stuck in an equilibrium below full employment for a long period, unemployment persists, and the market’s self-correction process is extremely slow or may never be completed at all.

货币主义者则继承了古典经济学的传统，认为从长期看价格和工资具有充分的灵活性，经济会自动回到”自然失业率”水平。弗里德曼强调，政府的需求管理政策存在认识时滞、决策时滞与生效时滞，等到政策发挥效果时经济形势可能已经反转，反而加剧了经济波动。因此政府干预不但无益，甚至是有害的。

Monetarists, by contrast, inherited the classical tradition and argued that in the long run prices and wages are fully flexible and the economy automatically returns to the “natural rate of unemployment”. Friedman stressed that government demand-management policy suffers from recognition lags, decision lags and implementation lags; by the time a policy takes effect the economic situation may already have reversed, so intervention actually amplifies fluctuations. Government intervention is therefore not merely useless but positively harmful.

这一分歧直接决定了双方的政策主张：凯恩斯主义者主张”逆风向”干预，在经济衰退时扩张需求；货币主义者则主张”规则优先”，让经济依靠自身机制调节。理解这一分歧，是理解后文所有具体争论的钥匙。

This disagreement directly determines each side’s policy prescriptions: Keynesians advocate “counter-cyclical” intervention, expanding demand during recessions, while monetarists advocate “rules first” and letting the economy adjust through its own mechanisms. Understanding this split is the key to understanding all the specific controversies that follow.

三、凯恩斯主义的核心：总需求管理与乘数效应 | The Keynesian Core: Aggregate Demand Management and the Multiplier

凯恩斯主义分析的总需求由消费、投资、政府支出与净出口四部分组成，即AD = C + I + G + (X – M)。凯恩斯认为，决定产出与就业水平的关键变量是总需求，而总需求本身不稳定，投资尤其受到”动物精神” – 即投资者非理性的乐观与悲观情绪 – 的支配，波动剧烈。

In the Keynesian framework, aggregate demand consists of consumption, investment, government spending and net exports, that is AD = C + I + G + (X – M). Keynes argued that the key determinant of output and employment is aggregate demand, and that aggregate demand is inherently unstable – investment in particular is driven by “animal spirits”, the irrational waves of optimism and pessimism among investors, and fluctuates violently.

当总需求不足时，凯恩斯主张政府应当扩大支出或减税来刺激需求，哪怕为此出现财政赤字。这是因为财政扩张具有”乘数效应”：政府每增加一元支出，会通过消费链条产生数倍于初始支出的国民收入增量，乘数大小取决于边际消费倾向，即k = 1/(1 – MPC)。在乘数作用下，政府支出对经济的拉动被放大。

When aggregate demand is deficient, Keynes argued that the government should expand spending or cut taxes to stimulate demand, even at the cost of running a budget deficit. This is because fiscal expansion has a “multiplier effect”: every additional yuan of government spending generates several times that amount in national income through the chain of consumption, and the size of the multiplier depends on the marginal propensity to consume, k = 1/(1 – MPC). Through the multiplier, government spending exerts a magnified stimulus on the economy.

此外，凯恩斯还提出了”流动性偏好理论”，认为人们持有货币出于交易、预防与投机三种动机，利率由货币供求决定。当经济陷入”流动性陷阱” – 利率已降至极低水平、货币政策失效时，财政政策就成为唯一可靠的刺激工具。这正是大萧条时期罗斯福新政的理论基础。

In addition, Keynes put forward the “liquidity preference theory”, holding that people hold money for transactional, precautionary and speculative motives, and that the interest rate is determined by the supply of and demand for money. When the economy falls into a “liquidity trap” – where interest rates are already at extremely low levels and monetary policy becomes ineffective – fiscal policy becomes the only reliable stimulus tool. This was the theoretical basis of Roosevelt’s New Deal during the Great Depression.

四、货币主义的核心：货币数量论与自然失业率 | The Monetarist Core: Quantity Theory of Money and the Natural Rate of Unemployment

货币主义的理论根基是”货币数量论”，其经典形式是费雪交易方程式MV = PY。其中M为货币供应量，V为货币流通速度，P为物价水平，Y为实际产出。货币主义者认为，长期内货币流通速度V是稳定的，实际产出Y由供给侧因素（技术、资本、劳动）决定，因此货币供应量的变化最终只会反映为物价水平的同比例变化。

The theoretical foundation of Monetarism is the “quantity theory of money”, whose classic form is Fisher’s equation of exchange, MV = PY, where M is the money supply, V is the velocity of circulation, P is the price level and Y is real output. Monetarists argue that in the long run velocity V is stable and real output Y is determined by supply-side factors such as technology, capital and labour, so changes in the money supply are ultimately reflected only in proportional changes in the price level.

弗里德曼由此得出名言：”通货膨胀无论何时何地都是一种货币现象。”他还提出了”自然失业率假说”：由于摩擦性失业与结构性失业的存在，经济中存在一个由劳动力市场结构决定的自然失业率，任何试图把失业率压到自然率之下的需求扩张，都只能以不断加速的通货膨胀为代价，并且只能奏效于短期。

From this Friedman drew his famous dictum: “Inflation is always and everywhere a monetary phenomenon.” He also advanced the “natural rate of unemployment hypothesis”: because frictional and structural unemployment exist, there is a natural rate of unemployment determined by the structure of the labour market, and any attempt to push unemployment below this natural rate through demand expansion can only be bought at the price of ever-accelerating inflation, and works only in the short run.

在政策主张上，货币主义者反对相机抉择的”微调”，主张实行固定的货币增长规则，让货币供应量按与经济增长率大致相当的速度稳定增长。他们认为，可预期的货币环境比频繁的政策干预更能稳定经济预期，从而降低通胀与失业的波动。

In terms of policy, Monetarists rejected discretionary “fine-tuning” and instead advocated a fixed money-growth rule, allowing the money supply to grow steadily at a rate roughly matching the growth of the economy. They believed that a predictable monetary environment stabilises expectations far better than frequent policy intervention, thereby reducing fluctuations in both inflation and unemployment.

五、菲利普斯曲线的两种解读 | Two Readings of the Phillips Curve

菲利普斯曲线最初描绘的是通货膨胀率与失业率之间的负相关关系：通胀上升时失业下降，反之亦然。20世纪50年代，新西兰经济学家菲利普斯利用英国近百年数据验证了这条向下倾斜的曲线，凯恩斯主义者据此认为政策制定者可以在通胀与失业之间进行”权衡取舍”，选择社会可以接受的组合。

The Phillips curve originally described a negative relationship between the inflation rate and the unemployment rate: as inflation rises unemployment falls, and vice versa. In the 1950s the New Zealand economist A. W. Phillips verified this downward-sloping curve using nearly a century of British data, and Keynesians concluded that policymakers could make a “trade-off” between inflation and unemployment, choosing a combination acceptable to society.

弗里德曼与费尔普斯则提出了”附加预期的菲利普斯曲线”。他们认为，短期内由于预期调整滞后，意外的通胀可以暂时降低失业；但长期中工人与企业会修正通胀预期，要求相应提高名义工资，失业率会回到自然失业率水平。因此长期菲利普斯曲线是一条位于自然失业率处的垂直线，通胀与失业之间不存在长期的权衡关系。

Friedman and Phelps instead proposed the “expectations-augmented Phillips curve”. They argued that in the short run, because expectations adjust with a lag, surprise inflation can temporarily reduce unemployment; but in the long run workers and firms revise their inflation expectations and demand correspondingly higher nominal wages, so unemployment returns to the natural rate. The long-run Phillips curve is therefore a vertical line at the natural rate of unemployment, and there is no long-run trade-off between inflation and unemployment.

20世纪70年代的滞胀为货币主义的观点提供了有力证据：失业率与通胀率同时上升，与原始菲利普斯曲线预测的替换关系明显矛盾。这一历史经验在CIE考试中经常被用来检验考生能否区分短期与长期菲利普斯曲线，并解释预期所起的关键作用。

The stagflation of the 1970s provided powerful evidence for the monetarist view: unemployment and inflation rose together, flatly contradicting the trade-off predicted by the original Phillips curve. This historical episode is frequently used in CIE examinations to test whether candidates can distinguish the short-run from the long-run Phillips curve and explain the crucial role played by expectations.

六、财政政策与货币政策之争 | Fiscal Policy versus Monetary Policy

两大流派对政策工具的选择截然不同。凯恩斯主义者认为财政政策是首选工具：政府支出直接构成总需求的一部分，乘数效应使其拉动作用强劲，而且在流动性陷阱中货币政策完全失效，只有财政政策能够推动经济走出衰退。财政扩张还能通过”挤入效应”提振私人部门信心。

The two schools differ completely in their choice of policy instruments. Keynesians regard fiscal policy as the tool of first resort: government spending directly forms part of aggregate demand, the multiplier effect makes its stimulus powerful, and in a liquidity trap monetary policy becomes completely ineffective so that only fiscal policy can push the economy out of recession. Fiscal expansion can also boost private-sector confidence through the “crowding-in effect”.

货币主义者则针锋相对地提出”挤出效应”：政府为赤字融资而借入资金，推高利率，从而挤占私人投资，财政扩张的总需求净效果可能接近于零。他们还批评财政政策时滞过长 – 从议会辩论到项目落地往往需要数年，政策出台时经济可能已经进入复苏，扩张性财政反而引发通胀。因此货币主义者主张以货币政策为主，并为其制定固定规则。

Monetarists counter with the “crowding-out effect”: when the government borrows to finance a deficit it drives up interest rates, which crowds out private investment, so the net effect of fiscal expansion on aggregate demand may be close to zero. They also criticise the long lags of fiscal policy – from parliamentary debate to project completion often takes years, by which time the economy may already be recovering, so expansionary fiscal policy merely ignites inflation. Monetarists therefore favour monetary policy as the primary tool, governed by a fixed rule.

现代经济学界的实际共识介于两者之间：多数中央银行采用”通货膨胀目标制”，以规则化的货币政策稳定物价；而财政政策在极端衰退（如2008年金融危机与新冠疫情）中仍被大规模启用。CIE考试常要求考生用AD-AS框架分析两种政策的相对有效性，并讨论挤出效应、流动性陷阱与政策时滞等评估要点。

Modern practice lies somewhere between the two schools: most central banks adopt “inflation targeting”, using rule-based monetary policy to stabilise prices, while fiscal policy is still deployed on a massive scale in extreme recessions such as the 2008 financial crisis and the COVID-19 pandemic. CIE examinations often ask candidates to analyse the relative effectiveness of the two policies within an AD-AS framework and to discuss evaluation points such as crowding-out, the liquidity trap and policy lags.

七、通货膨胀成因的不同解释 | Explaining Inflation: Two Views

凯恩斯主义者将通货膨胀区分为”需求拉动型”与”成本推动型”。需求拉动型通胀源于总需求超过潜在产出，经济过热；成本推动型通胀则源于工资、原材料等成本上升，企业将成本转嫁给消费者。凯恩斯主义者还强调”工资-价格螺旋”：工人要求加薪以抵消物价上涨，加薪又推高成本与物价，形成自我强化的循环。

Keynesians distinguish “demand-pull” from “cost-push” inflation. Demand-pull inflation arises when aggregate demand exceeds potential output and the economy overheats; cost-push inflation arises when costs such as wages and raw materials rise and firms pass the increase on to consumers. Keynesians also stress the “wage-price spiral”: workers demand pay rises to offset rising prices, the pay rises push up costs and prices again, and a self-reinforcing loop is created.

货币主义者则坚持单一解释：通胀的根源是货币供应量增长过快，”过多的货币追逐过少的商品”。他们认为成本推动型通胀本质上只是相对价格调整，除非央行通过扩张货币供给予以”迁就”，否则不可能演变为持续的通胀。因此治理通胀的药方只有一个 – 控制货币增长，而不是收入政策或价格管制。

Monetarists insist on a single explanation: inflation is rooted in money supply growing too fast – “too much money chasing too few goods”. They argue that cost-push inflation is essentially only a relative price adjustment and cannot become persistent inflation unless the central bank “accommodates” it by expanding the money supply. The remedy for inflation is therefore singular – control money growth – rather than incomes policies or price controls.

这一分歧的政策含义非常实际：凯恩斯主义者可能支持工资管制、补贴等供给端措施来抑制成本推动型通胀，而货币主义者主张央行紧缩货币并建立反通胀的信誉。20世纪80年代初，美联储主席沃尔克正是以货币紧缩政策制服了美国的两位数通胀，成为货币主义政策主张的经典案例。

The policy implications of this disagreement are very practical: Keynesians may support wage controls, subsidies and other supply-side measures to suppress cost-push inflation, while monetarists urge central banks to tighten money and build anti-inflation credibility. In the early 1980s the Federal Reserve chairman Paul Volcker tamed double-digit US inflation precisely through monetary tightening, a classic case of monetarist policy in action.

八、对经济周期与失业的不同看法 | Business Cycles and Unemployment: Competing Views

凯恩斯主义者认为经济周期主要由需求冲击驱动：投资波动、出口变化或信心崩溃都会通过乘数-加速数机制放大为剧烈的周期性波动。更重要的是，凯恩斯主义者认为衰退造成的失业并非暂时的”摩擦”，而是会留下长期疤痕 – 工人技能退化、与劳动力市场脱节，即”滞后效应”，因此自然失业率本身也会因衰退而上升。

Keynesians believe the business cycle is driven mainly by demand shocks: fluctuations in investment, changes in exports or collapses in confidence are amplified through the multiplier-accelerator mechanism into violent cyclical swings. More importantly, they argue that the unemployment caused by recessions is not temporary “friction” but leaves permanent scars – workers lose skills and become detached from the labour market, a phenomenon known as “hysteresis” – so the natural rate itself rises as a result of recession.

货币主义者则认为，经济周期主要是货币冲击的结果：央行突然改变货币供应量，使实际物价与人们预期的物价出现偏差，从而暂时扭曲产出与就业。一旦预期修正，经济便回到自然率水平，因此政府没有必要也没有能力”熨平”经济周期。他们主张用稳定的货币规则消除货币冲击这一周期根源。

Monetarists, in contrast, argue that the business cycle is chiefly the result of monetary shocks: when the central bank suddenly changes the money supply, the actual price level diverges from what people expected, temporarily distorting output and employment. Once expectations are corrected the economy returns to the natural rate, so governments neither need to nor can “iron out” the cycle. They advocate a stable money rule to remove the monetary source of cyclical fluctuations altogether.

对考生而言，理解这一争论有助于回答”政府是否应该干预经济周期”这类评价题：支持干预可引用市场失灵、滞后效应与乘数效应；反对干预可引用政策时滞、理性预期与挤出效应。能够同时呈现双方论据并作出有条件的判断，正是CIE高分答案的典型特征。

For candidates, understanding this debate helps answer evaluative questions such as “should governments intervene in the business cycle”: those in favour can cite market failure, hysteresis and the multiplier effect; those against can cite policy lags, rational expectations and crowding-out. Presenting the arguments of both sides and reaching a conditional judgement is the hallmark of a top-grade CIE answer.

九、CIE 考试答题框架：如何比较两大流派 | CIE Exam Framework: Comparing the Two Schools

在CIE A-Level经济学试卷中，与两大流派相关的典型题目包括：评价”财政政策比货币政策更能稳定经济”这一观点；解释为什么长期菲利普斯曲线是垂直的；分析需求管理政策在滞胀时期为何失效；以及讨论货币主义政策主张在当代的适用性。这些题目都属于论文题（essay question），需要完整的分析结构与评价。

Typical CIE A-Level Economics questions related to the two schools include: evaluate the view that fiscal policy is more effective than monetary policy in stabilising the economy; explain why the long-run Phillips curve is vertical; analyse why demand-management policies failed during stagflation; and discuss the relevance of monetarist prescriptions today. These are essay questions requiring a complete analytical structure and evaluation.

一个高分的答题框架可以概括为四步。第一步，明确定义关键概念 – 总需求、自然失业率、货币数量论、流动性陷阱等，并配以AD-AS图或菲利普斯曲线图。第二步，分别阐述两大流派的理论逻辑与政策主张，确保双方论据都得到充分呈现。第三步，用现实案例（大萧条、70年代滞胀、2008年金融危机）检验理论。第四步，评估局限并给出有条件结论，例如”财政政策在流动性陷阱中更有效，但在正常时期可能被挤出效应削弱”。

A top-grade answer framework can be summarised in four steps. First, define the key concepts precisely – aggregate demand, the natural rate of unemployment, the quantity theory of money, the liquidity trap – and support them with AD-AS or Phillips curve diagrams. Second, set out the theoretical logic and policy prescriptions of both schools, giving full weight to each side. Third, test the theories against real-world episodes such as the Great Depression, the stagflation of the 1970s and the 2008 financial crisis. Fourth, evaluate the limitations and reach a conditional conclusion, for example “fiscal policy is more effective in a liquidity trap, but in normal times its effect may be weakened by crowding-out”.

此外，考生应熟练使用以下高频术语：乘数效应、挤出效应、政策时滞、理性预期、适应性预期、自然失业率、NAIRU（非加速通货膨胀失业率）、货币流通速度、通货膨胀目标制。正确且灵活地运用这些术语，是向阅卷者展示深度理解的最快捷方式。

In addition, candidates should master the following high-frequency terms: multiplier effect, crowding-out, policy lags, rational expectations, adaptive expectations, natural rate of unemployment, NAIRU (non-accelerating inflation rate of unemployment), velocity of circulation and inflation targeting. Using these terms correctly and flexibly is the fastest way to demonstrate depth of understanding to the examiner.

十、现代经济学中的融合与争论 | The Modern Synthesis and the Debate Today

今天的主流经济学并非简单二选一。以萨缪尔森为代表的”新古典综合派”早已将凯恩斯的短期需求分析与古典的长期供给分析结合起来：短期看需求，长期看供给。新凯恩斯主义者吸收理性预期假设，用菜单成本、工资刚性等微观基础重新论证了市场失灵与干预的必要性；而货币主义的思想则通过通货膨胀目标制融入了各国央行的操作框架。

Mainstream economics today is not a simple either-or choice. The “neoclassical synthesis” associated with Samuelson long ago combined Keynesian short-run demand analysis with classical long-run supply analysis: demand in the short run, supply in the long run. New Keynesians absorbed the rational expectations hypothesis and rebuilt the case for market failure and intervention on microfoundations such as menu costs and wage stickiness, while monetarist ideas entered the operating framework of central banks through inflation targeting.

2008年全球金融危机与2020年新冠疫情再次把凯恩斯主义推回政策舞台中央：各国政府大规模举债刺激需求，中央银行实施量化宽松。但与此同时，货币超发引发的新一轮通胀担忧又让弗里德曼的警告重新获得关注。这场百年争论至今仍在延续，而其每次轮回都为经济学考试提供了鲜活的分析素材。

The 2008 global financial crisis and the 2020 COVID-19 pandemic pushed Keynesianism back to the centre of the policy stage: governments borrowed massively to stimulate demand and central banks launched quantitative easing. At the same time, fears of a new round of inflation caused by excessive money creation have revived interest in Friedman’s warnings. This century-long debate continues to this day, and each of its turns provides fresh material for economics examinations.

对准备CIE考试的同学来说，掌握两大流派的理论脉络、政策主张与适用条件，不仅是为了应对考试，更是理解现实世界宏观经济政策的一把钥匙。无论未来从事金融、咨询还是公共政策工作，这种”从理论到政策再到现实检验”的思维方式都将持续发挥价值。

For students preparing for the CIE examination, mastering the theoretical threads, policy prescriptions and applicability conditions of the two schools is not only a way to ace the exam but also a key to understanding real-world macroeconomic policy. Whether you go on to work in finance, consulting or public policy, this way of thinking – from theory to policy to testing against reality – will continue to pay dividends.

Summary | 总结

凯恩斯主义与货币主义围绕市场能否自我修复这一根本问题展开争论：凯恩斯主义强调总需求管理、财政政策与乘数效应，认为市场存在失灵，政府必须积极干预；货币主义强调货币数量论、自然失业率与预期的作用，认为通胀是货币现象，政府干预弊大于利。两大流派在菲利普斯曲线、政策工具选择与通胀成因等问题上提出了截然不同的分析框架。

Keynesianism and Monetarism disagree fundamentally over whether markets can self-correct: Keynesianism stresses aggregate demand management, fiscal policy and the multiplier effect, arguing that markets fail and governments must intervene actively; Monetarism stresses the quantity theory of money, the natural rate of unemployment and the role of expectations, arguing that inflation is a monetary phenomenon and that government intervention does more harm than good. The two schools offer sharply different analytical frameworks on the Phillips curve, the choice of policy instruments and the causes of inflation.

对于CIE考生，建议把两大流派的核心概念、政策主张与历史案例整理成对比表格反复记忆，并在论文题中坚持”定义-理论-案例-评价”的四步结构。理解争论双方，而不是记住单一结论，是获得高分的关键，也是真正理解宏观经济学的起点。

For CIE candidates, we recommend organising the core concepts, policy prescriptions and historical cases of the two schools into a comparison table for repeated revision, and sticking to the four-step “define – theory – evidence – evaluate” structure in essay answers. Understanding both sides of the debate, rather than memorising a single conclusion, is the key to high marks and the true starting point for understanding macroeconomics.

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