The Phillips Curve Explained | 菲利普斯曲线解析

📚 The Phillips Curve Explained | 菲利普斯曲线解析

The Phillips curve is one of the most famous and contested relationships in macroeconomics. It describes an empirical inverse relationship between the rate of unemployment and the rate of wage (or price) inflation in an economy. For A-Level students, mastering this curve is essential for understanding the macroeconomic trade-offs that policymakers face when managing inflation and employment.

菲利普斯曲线是宏观经济学中最著名、也最具争议的关系之一。它描述了经济体中失业率与工资（或价格）通胀率之间经验性的反向关系。对于A-Level学生而言，掌握该曲线是理解政策制定者在调控通胀与就业时所面临权衡的关键。

1. What Is the Phillips Curve? | 什么是菲利普斯曲线？

The Phillips curve plots the rate of inflation (π) on the vertical axis against the rate of unemployment (u) on the horizontal axis. In its original form, the curve slopes downward from left to right, indicating that a lower unemployment rate is associated with a higher inflation rate, and vice versa.

菲利普斯曲线以纵轴表示通胀率（π），横轴表示失业率（u）。在其原始形式中，曲线自左向右下倾斜，表明较低的失业率伴随着较高的通胀率，反之亦然。

The economic intuition behind this relationship is straightforward: when the economy operates near full employment, labour becomes scarce, giving workers greater bargaining power to demand higher wages. Firms pass these higher labour costs on to consumers in the form of higher prices, thereby generating inflation.

这一关系背后的经济直觉很直接：当经济接近充分就业时，劳动力变得稀缺，工人在要求更高工资方面拥有更强的议价能力。企业将这些更高的劳动力成本以更高价格的形式转嫁给消费者，从而产生通胀。

2. The Original Phillips Curve (1958) | 原始菲利普斯曲线（1958年）

In 1958, the New Zealand-born economist Alban William Phillips used data from the United Kingdom between 1861 and 1957 to document a stable negative relationship between the rate of unemployment and the rate of change in money wages. His findings suggested that the trade-off was remarkably stable over nearly a century.

1958年，新西兰出生的经济学家奥尔本·威廉·菲利普斯利用英国1861年至1957年的数据，记录了失业率与货币工资变化率之间稳定的负相关关系。他的研究结果表明，这一权衡在近一个世纪内异常稳定。

Later economists, including Paul Samuelson and Robert Solow, adapted Phillips’ work to price inflation rather than wage inflation, giving rise to the version of the curve that appears in modern textbooks. They argued that governments could ‘choose’ between different combinations of inflation and unemployment along the curve.

后来，包括保罗·萨缪尔森和罗伯特·索洛在内的经济学家将菲利普斯的研究从工资通胀拓展到价格通胀，从而形成了现代教科书中的曲线版本。他们认为政府可以在曲线上”选择”不同的通胀与失业组合。

3. The Short-Run Phillips Curve | 短期菲利普斯曲线

The short-run Phillips curve (SRPC) shows the inverse relationship between inflation and unemployment when expectations of inflation are held constant. It is typically drawn with a downward slope and is based on the assumption that nominal wages are sticky in the short run.

短期菲利普斯曲线（SRPC）在通胀预期保持不变的条件下，展示通胀与失业之间的反向关系。它通常被绘制为向下倾斜的曲线，其基础假设是名义工资在短期内具有粘性。

Along the SRPC, a government can reduce unemployment through expansionary demand-side policies, such as lower interest rates or increased government spending. However, this comes at the cost of higher inflation. Conversely, contractionary policies can reduce inflation but will increase unemployment.

沿SRPC，政府可以通过扩张性需求侧政策（如降低利率或增加政府支出）来降低失业率，但代价是更高的通胀。相反，紧缩性政策可以降低通胀，却会推高失业率。

The SRPC assumes money illusion: workers fail to recognise that rising nominal wages are matched by rising prices, so they increase labour supply based on higher nominal pay.
SRPC假设存在货币幻觉：工人未能认识到名义工资的上涨与物价上涨是同步的，因此他们基于更高的名义工资增加劳动供给。

π = πᵉ – β(u – u*) + ε

In the expectations-augmented equation above, π is the actual inflation rate, πᵉ is expected inflation, u is the current unemployment rate, u* is the natural rate of unemployment, β is a positive constant, and ε represents supply shocks. When u is below u*, inflation exceeds expectations.

在上述预期增强方程中，π为实际通胀率，πᵉ为预期通胀率，u为当前失业率，u*为自然失业率，β为正常数，ε代表供给冲击。当u低于u*时，实际通胀会高于预期。

4. The Expectations-Augmented Phillips Curve | 预期增强的菲利普斯曲线

In the late 1960s, Milton Friedman and Edmund Phelps independently challenged the stability of the Phillips curve trade-off. They argued that workers and firms form expectations about future inflation and adjust their behaviour accordingly, undermining the simple inverse relationship.

在20世纪60年代末，米尔顿·弗里德曼和埃德蒙·费尔普斯分别对菲利普斯曲线的稳定性提出了挑战。他们认为工人和企业会对未来通胀形成预期并相应调整行为，从而削弱了简单的反向关系。

Friedman distinguished between the short-run and long-run Phillips curves. In the short run, if actual inflation exceeds expected inflation, workers are ‘fooled’ into accepting nominal wage increases they mistake for real wage gains, so unemployment falls. However, once expectations adjust upward, workers demand even higher nominal wages, and unemployment returns to its natural rate.

弗里德曼区分了短期与长期菲利普斯曲线。在短期，如果实际通胀高于预期通胀，工人被”欺骗”，误将名义工资的上涨当作实际工资的增长，因此失业率下降。然而，一旦预期向上调整，工人要求更高的名义工资，失业率便回归其自然水平。

5. The Long-Run Phillips Curve | 长期菲利普斯曲线

The long-run Phillips curve (LRPC) is vertical at the natural rate of unemployment (u*). This verticality implies that no permanent trade-off exists between inflation and unemployment in the long run: attempts to keep unemployment below u* will merely cause accelerating inflation.

长期菲利普斯曲线（LRPC）在自然失业率（u*）处垂直。这种垂直性意味着长期内通胀与失业之间不存在永久性的权衡：试图将失业率保持在u*以下只会导致通胀加速上升。

The vertical LRPC has profound policy implications. It suggests that demand-side management cannot permanently reduce unemployment below the natural rate; any such attempt will be ‘bought’ at the cost of ever-increasing inflation. This idea is central to the concept of stagflation observed in the 1970s.

垂直的LRPC具有深远的政策含义。它表明需求侧管理无法将失业率永久降至自然率以下；任何此类尝试都将以不断攀升的通胀为代价。这一思想是理解20世纪70年代”滞胀”现象的核心。

特征	短期SRPC	长期LRPC
形状	向下倾斜	垂直
预期调整	预期固定不变	预期完全调整
政策含义	存在权衡，可选择组合	无权衡，失业回归自然率

6. Shifts in the Phillips Curve | 菲利普斯曲线的移动

Changes in the expected rate of inflation cause the short-run Phillips curve to shift. For example, an increase in inflation expectations shifts the SRPC to the right: for any given unemployment rate, the associated inflation rate is now higher.

预期通胀率的变动会引起短期菲利普斯曲线的移动。例如，通胀预期的上升会使SRPC右移：在任一给定的失业率下，对应的通胀率现在更高了。

Supply-side shocks, such as an oil price spike, also shift the Phillips curve. A negative supply shock raises production costs and increases inflation while simultaneously pushing unemployment upward, causing both the SRPC and the natural rate itself to change.

供给侧冲击，例如油价飙升，同样会使菲利普斯曲线发生移动。负向供给冲击提高了生产成本并推高通胀，同时使失业率上升，导致SRPC乃至自然失业率本身都发生变化。

An increase in expected inflation (πᵉ) → SRPC shifts right/upward.
预期通胀上升（πᵉ上升）→ SRPC向右/向上移动。
A positive supply shock reduces inflation and shifts the SRPC left/downward.
正向供给冲击降低通胀，使SRPC向左/向下移动。

7. Policy Implications | 政策含义

The Phillips curve framework provides a foundation for evaluating macroeconomic policy trade-offs. Consider a government that wishes to reduce unemployment from its current level to below the natural rate. According to the short-run curve, an expansionary fiscal or monetary policy can achieve this, but at the cost of higher inflation.

菲利普斯曲线框架为评估宏观政策权衡奠定了基础。假设政府希望将失业率从当前水平降至自然率以下。根据短期曲线，扩张性财政或货币政策可以实现这一目标，但代价是更高的通胀。

In the long run, however, workers and firms revise their inflation expectations upward. The economy moves along the vertical LRPC, and unemployment returns to u* — only with a permanently higher inflation rate. This explains why sustained demand-side stimulus leads to accelerating inflation rather than permanent employment gains.

然而在长期中，工人和企业会向上修正其通胀预期。经济沿着垂直的LRPC运行，失业率回归u*——只是通胀率永久性地更高了。这解释了为什么持续的需求侧刺激会导致通胀加速而非持久增加就业。

Consequently, many modern central banks adopt inflation-targeting frameworks rather than attempting to exploit the Phillips curve trade-off. Credible commitments to low inflation help anchor inflation expectations, thereby making the short-run trade-off less favourable to policymakers.

因此，许多现代中央银行采用通胀目标制框架，而非试图利用菲利普斯曲线的权衡。对低通胀的可靠承诺有助于锚定通胀预期，从而使短期权衡对政策制定者而言不再那么”有利可图”。

8. Real-World Evidence | 现实数据证据

The original Phillips curve relationship appeared to hold reasonably well in the 1960s, but it broke down dramatically in the 1970s. During the oil price shocks of 1973–74 and 1979, the UK and the US experienced simultaneously rising inflation and unemployment — a combination known as stagflation that the simple Phillips curve could not explain.

原始菲利普斯曲线关系在20世纪60年代看起来相当稳健，但在20世纪70年代被彻底打破。在1973–74年和1979年石油价格冲击期间，英国和美国同时经历了通胀与失业的上升——这种被称为”滞胀”的组合是简单菲利普斯曲线无法解释的。

The expectations-augmented Phillips curve, however, can explain stagflation: the negative supply shock increased both inflation and unemployment, shifting the SRPC outward. When central banks tried to push unemployment back down, they only succeeded in raising inflation expectations and accelerating price growth.

然而，预期增强的菲利普斯曲线能够解释滞胀：负向供给冲击同时推高了通胀和失业率，使SRPC向外移动。当央行试图将失业率压回低位时，它们只成功推高了通胀预期并加速了物价上涨。

9. Criticisms and Limitations | 批评与局限性

Despite its influence, the Phillips curve has faced substantial criticism. First, the natural rate of unemployment is not directly observable and can change over time due to structural shifts, technological change, and hysteresis effects — where prolonged high unemployment permanently raises the natural rate.

尽管菲利普斯曲线影响深远，但它也面临大量批评。首先，自然失业率无法直接观测，而且会因结构性变化、技术变革以及”滞后效应”（即长期高失业永久性推高自然失业率）而随时间改变。

Second, the curve assumes that expectations are formed in a particular way. Adaptive expectations — where people base predictions on past inflation — differ from rational expectations, which presume people use all available information, including knowledge of policy rules. Under rational expectations, even the short-run curve may not offer the predicted trade-off.

其次，该曲线假设预期以某种特定方式形成。适应性预期（人们基于过去的通胀进行预测）与理性预期（人假定人们利用所有可得信息，包括对政策规则的认知）不同。在理性预期之下，即使短期曲线也可能不提供所预测的权衡。

Third, the Phillips curve relationship has weakened in recent decades. Many advanced economies have experienced low inflation alongside modest unemployment rates, creating what economists call a ‘flattening’ of the Phillips curve. Globalisation, digitalisation, and flexible labour markets have all been cited as contributing factors.

第三，菲利普斯曲线关系在近几十年有所弱化。许多发达经济体经历了低通胀与温和失业率并存的情况，经济学家称之为菲利普斯曲线的”平坦化”。全球化、数字化和灵活劳动力市场均被认为是促成因素。

10. Conclusion | 结论

The Phillips curve remains an indispensable tool for A-Level Economics students because it bridges the gap between abstract theory and real macroeconomic policy. Understanding the difference between the short-run and long-run curves, as well as the role of inflation expectations, enables students to critically evaluate policy decisions such as quantitative easing, interest rate changes, and fiscal stimulus.

菲利普斯曲线仍然是A-Level经济学生不可或缺的工具，因为它弥合了抽象理论与现实宏观经济政策之间的鸿沟。理解短期与长期曲线的区别，以及通胀预期的作用，使学生能够批判性地评估量化宽松、利率变动和财政刺激等政策决策。

For examinations, remember the four key points: the short-run curve slopes downward; the long-run curve is vertical at u*; expectations shift the curve; and supply shocks can cause both inflation and unemployment to rise together. Mastering these insights will serve you well in both exams and essay questions.

在考试中，请记住四个关键要点：短期曲线向下倾斜；长期曲线在u*处垂直；预期会移动曲线；供给冲击可使通胀与失业同时上升。掌握这些洞见将助力你在考试和论文题中游刃有余。

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The Phillips Curve Explained | 菲利普斯曲线解析