The Phillips Curve

Introduction: Why do inflation and unemployment seem linked? 📉📈

students, imagine a country trying to keep prices stable while also helping more people find jobs. Governments and central banks often want both low unemployment and low inflation, but these goals can sometimes conflict. The Phillips Curve helps explain why that conflict can happen. It shows a relationship between inflation and unemployment, and it is one of the most important ideas in Long-Run Consequences of Stabilization Policies.

Learning objectives

By the end of this lesson, students, you should be able to:

Explain the main ideas and terminology behind the Phillips Curve.
Apply AP Macroeconomics reasoning to problems involving the Phillips Curve.
Connect the Phillips Curve to fiscal and monetary policy decisions.
Summarize how the Phillips Curve fits into long-run economic analysis.
Use evidence and examples to explain the trade-offs shown by the Phillips Curve.

A big AP Macroeconomics question is this: Can policymakers lower unemployment without causing inflation? The Phillips Curve helps answer that question, especially when we think about short-run and long-run effects.

What the Phillips Curve shows

The Phillips Curve is a model that shows an inverse relationship between inflation and unemployment. In simple terms, when unemployment is low, inflation tends to be higher; when unemployment is high, inflation tends to be lower. This happens because strong demand for goods, services, and workers can push wages and prices up.

The original idea came from economist A. W. Phillips, who studied data from the United Kingdom. He noticed that periods of low unemployment were often associated with higher wage growth. Later economists expanded this idea to include price inflation instead of just wage inflation.

A simple way to think about it is this:

$$\text{Lower unemployment} \rightarrow \text{Higher inflation}$$

and

$$\text{Higher unemployment} \rightarrow \text{Lower inflation}$$

This relationship is most useful in the short run. In the long run, the trade-off may disappear or become much weaker.

Real-world example

Suppose the economy is weak and many people are out of work. Firms do not need to compete as hard for workers, so wages grow slowly. With weaker consumer demand, businesses also have less reason to raise prices quickly. That can lead to lower inflation. Now imagine the economy is booming, stores are crowded, and firms are hiring quickly. Workers may get higher wages, and firms may raise prices because demand is strong. That can lead to higher inflation.

The short-run Phillips Curve and stabilization policy

The short-run Phillips Curve is the version most closely connected to stabilization policies. Stabilization policies are actions the government or central bank uses to reduce economic fluctuations. These include:

Expansionary fiscal policy: increasing government spending or cutting taxes
Expansionary monetary policy: increasing the money supply or lowering interest rates
Contractionary fiscal policy: decreasing government spending or raising taxes
Contractionary monetary policy: decreasing the money supply or raising interest rates

When policymakers use expansionary policy to reduce unemployment, they may increase aggregate demand. Higher aggregate demand can raise output and reduce unemployment in the short run, but it can also increase inflation. That is the short-run trade-off shown by the Phillips Curve.

AP-style reasoning example

Suppose the economy has a recessionary gap. The central bank lowers interest rates. As borrowing becomes cheaper, households buy more goods and firms invest more. Aggregate demand rises, output increases, and unemployment falls. But if demand rises faster than the economy’s ability to produce, prices may rise too. This means inflation increases.

In AP Macroeconomics, you should connect this to the idea that policies aimed at reducing unemployment can have the side effect of higher inflation. That is a core Phillips Curve insight.

The long-run Phillips Curve and natural rate of unemployment

The long-run Phillips Curve is very different from the short-run curve. In the long run, economists often describe the Phillips Curve as vertical at the natural rate of unemployment.

The natural rate of unemployment is the unemployment rate that exists when the economy is producing at its potential output. It includes frictional unemployment and structural unemployment, but not cyclical unemployment.

A vertical long-run Phillips Curve means that, in the long run, there is no permanent trade-off between inflation and unemployment. If policymakers try to keep unemployment below the natural rate for too long, inflation may continue to rise, but unemployment will eventually move back toward its natural rate.

We can represent the long-run idea like this:

$$u = u_n$$

where $u$ is the unemployment rate and $u_n$ is the natural rate of unemployment.

This matters a lot for stabilization policy because it shows that policies can change unemployment temporarily, but they cannot permanently push unemployment below the natural rate without causing accelerating inflation.

Why the long run matters

Imagine a government keeps using expansionary policy to keep unemployment unusually low. At first, workers and firms may not fully expect the higher inflation. But over time, people adjust wages, prices, and expectations. Once expectations change, unemployment tends to return toward its natural rate, while inflation remains higher than before. This is why long-run effects are so important in macroeconomics.

Expectations and the shifting Phillips Curve

The Phillips Curve does not stay fixed forever. One major reason is expectations. If workers and firms expect higher inflation, they act in ways that can make inflation happen.

For example, workers may demand higher wages if they expect prices to rise. Firms may raise prices in advance if they expect their costs to increase. These expectations can shift the short-run Phillips Curve.

This is often connected to the idea of the expected inflation rate. When expected inflation rises, the short-run Phillips Curve can shift upward, meaning that at any given unemployment rate, inflation tends to be higher.

A useful AP formula-style relationship is:

$$\pi = \pi^e - \alpha(u - u_n)$$

where:

$\pi$ = actual inflation
$\pi^e$ = expected inflation
$\alpha$ = a positive constant
$u$ = unemployment rate
$u_n$ = natural rate of unemployment

This equation shows that if unemployment is below the natural rate, inflation tends to rise above expected inflation. If unemployment is above the natural rate, inflation tends to fall below expected inflation.

Simple interpretation

If $u < u_n$, then $\pi$ tends to be higher.

If $u > u_n$, then $\pi$ tends to be lower.

This helps explain why a policy that works in the short run may not work the same way later. As expectations adjust, the economy can move to a new long-run outcome.

Connecting the Phillips Curve to stabilization policies

The Phillips Curve is closely linked to the long-run consequences of policy because it shows that policymakers may face temporary trade-offs.

Expansionary policy

Expansionary fiscal or monetary policy can:

Increase aggregate demand
Lower unemployment in the short run
Raise inflation in the short run

Contractionary policy

Contractionary fiscal or monetary policy can:

Decrease aggregate demand
Raise unemployment in the short run
Lower inflation in the short run

This is why policymakers must make hard choices. For example, during a recession, expansionary policy can help people find jobs more quickly. But if the economy is already near full employment, the same policy may create too much inflation.

Real-world example

In a period of high unemployment, a central bank might cut interest rates to stimulate spending. This can reduce unemployment, but if the economy later overheats, inflation may speed up. To slow inflation, the central bank may then raise interest rates. That can reduce inflation but may also increase unemployment temporarily.

students, this is the core stabilization policy dilemma: actions that help one goal in the short run may hurt the other goal.

Important AP takeaways and common mistakes

The Phillips Curve is often tested in AP Macroeconomics because it helps explain policy trade-offs. To use it correctly, remember these points:

The short-run Phillips Curve shows a trade-off between inflation and unemployment.
The long-run Phillips Curve is vertical at the natural rate of unemployment.
Expansionary policy can reduce unemployment but may raise inflation.
Contractionary policy can reduce inflation but may raise unemployment.
Expectations matter because they can shift the short-run Phillips Curve.

A common mistake is thinking that policymakers can permanently choose any combination of low inflation and low unemployment. The long-run Phillips Curve shows that this is not true. Another mistake is forgetting that the natural rate of unemployment is not zero. Even a healthy economy has some unemployment due to job changes and skill mismatches.

Conclusion

The Phillips Curve is one of the clearest tools for understanding the long-run consequences of stabilization policies. It shows that low unemployment and low inflation are often hard to achieve at the same time, especially in the short run. It also teaches an important long-run lesson: trying to push unemployment below its natural rate can lead to higher inflation without a lasting unemployment benefit.

For AP Macroeconomics, students, the key idea is not just memorizing the curve. You need to explain what causes it to shift, how fiscal and monetary policy affect it, and why long-run outcomes differ from short-run outcomes. That is why the Phillips Curve is such an important part of macroeconomic analysis. ✅

Study Notes

The Phillips Curve shows an inverse relationship between inflation and unemployment in the short run.
Lower unemployment often comes with higher inflation, and higher unemployment often comes with lower inflation.
Stabilization policies can shift aggregate demand and affect both unemployment and inflation.
The short-run Phillips Curve reflects a trade-off; the long-run Phillips Curve is vertical at the natural rate of unemployment.
The natural rate of unemployment includes frictional and structural unemployment.
Expected inflation affects the position of the short-run Phillips Curve.
A useful relationship is $\pi = \pi^e - \alpha(u - u_n)$.
Expansionary policy can reduce unemployment but may raise inflation.
Contractionary policy can reduce inflation but may raise unemployment.
In the long run, unemployment tends to return to the natural rate.
The Phillips Curve helps explain why macroeconomic policy often involves trade-offs and timing effects.