In macroeconomic analysis and monetary policy, the Phillips Curve is an empirical and theoretical model representing the relationship between the rate of inflation and the rate of unemployment in a national economy. The concept originated from an influential 1958 empirical investigation conducted by New Zealand-born economist A.W. Phillips (Alban William Housego Phillips), published in Economica under the title "The Relation Between Unemployment and the Rate of Change of Money Wage Rates in the United Kingdom, 1861–1957." Phillips discovered a persistent historical inverse correlation: when national unemployment was low, money wage rates grew rapidly, and when unemployment was high, wage inflation slowed markedly. Economists Paul Samuelson and Robert Solow soon modified the framework by substituting general price inflation for wage growth, establishing the downward-sloping Phillips Curve as an operational blueprint for Keynesian demand management in the 1960s.
The initial formulation suggested that economic policymakers faced an exploitable menu of choices: governments could permanently achieve lower unemployment by tolerating higher inflation, or suppress inflation at the cost of elevated joblessness. However, this simplistic trade-off broke down during the 1970s global stagflation, triggered by supply-side crude oil price shocks that produced simultaneous double-digit inflation and escalating unemployment. Economists Milton Friedman and Edmund Phelps had independently predicted this collapse in 1968 through the Natural Rate Hypothesis. They demonstrated that while an inverse relationship exists in the short run (Short-Run Phillips Curve), economic agents eventually adjust their inflation expectations. Once workers incorporate expected inflation into future wage negotiations, unemployment returns to its structural equilibrium, known as the Natural Rate of Unemployment or NAIRU (Non-Accelerating Inflation Rate of Unemployment).
In the long run, the Phillips Curve is completely vertical at the natural rate of unemployment, indicating that monetary expansion cannot permanently increase employment beyond structural capacity. Attempts by central banks to drive unemployment below NAIRU through sustained monetary stimulus generate accelerating inflation with zero permanent employment gains. Robert Lucas and the rational expectations school further reinforced this insight through the Lucas Critique, demonstrating that forward-looking economic agents anticipate predictable policy shifts. Modern central banking, including the Reserve Bank of India under its Flexible Inflation Targeting (FIT) statutory framework under Section 45ZA of the RBI Act, focuses on anchoring medium-term inflation expectations at four percent rather than attempting to manipulate short-run employment trade-offs.
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The Phillips Curve illustrates the macroeconomic relationship between the rate of inflation and the rate of unemployment.
A.W. Phillips published the original empirical curve in 1958 based on UK money wage and unemployment data from 1861 to 1957.
Paul Samuelson and Robert Solow adapted the curve in 1960 to link general price inflation with unemployment rates.
The traditional Short-Run Phillips Curve (SRPC) is downward-sloping, indicating an inverse trade-off between inflation and unemployment.
Lower unemployment increases bargaining power for workers, pushing up wages and driving demand-pull and cost-push inflation.
The 1970s stagflation, driven by OPEC oil supply shocks, witnessed simultaneous high inflation and high unemployment, breaking the simple Phillips Curve.
Milton Friedman and Edmund Phelps independently proposed the Natural Rate Hypothesis in 1968, challenging the permanent trade-off.
NAIRU stands for the Non-Accelerating Inflation Rate of Unemployment, representing the rate below which inflation accelerates.
The Long-Run Phillips Curve (LRPC) is vertical at the natural rate of unemployment, indicating no long-run trade-off exists.
Adaptive expectations theory suggests workers base future inflation expectations on past observed inflation rates.
Rational expectations theory, pioneered by John Muth and Robert Lucas, asserts individuals use all available information to forecast inflation.
The Lucas Critique argues that historical empirical relationships cannot predict the effects of systematic economic policy changes.
When an economy experiences a negative supply shock, the short-run Phillips curve shifts outward and upward to the right.
Frictional and structural unemployment make up the natural rate of unemployment, which cannot be eliminated by monetary expansion.
Central bank credibility is essential for anchoring inflation expectations and flattening the short-run Phillips curve.
The sacrifice ratio measures the percentage of one year GDP that must be foregone to reduce inflation by one percentage point.
In recent decades, many developed economies observed a flattening of the Phillips Curve, where large unemployment swings caused minimal inflation changes.
India adopted Flexible Inflation Targeting (FIT) in 2016 under Section 45ZA of the RBI Act, setting a 4% consumer price index target within a +/-2% band.
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