LRPC in Economics- Long-Run Aggregate Supply
What the LRPC Actually Is (And Why It Matters)
The Long-Run Phillips Curve (LRPC) is a graph showing that in the long run, there's no tradeoff between inflation and unemployment. The unemployment rate settles at its natural rate regardless of inflation. That's the bitter truth economists have to face.
Economists spent years chasing the idea that you could permanently lower unemployment by accepting higher inflation. The 1970s shattered that illusion. When governments tried to exploit the short-run tradeoff, they got stagflation instead—high unemployment and high inflation hitting at the same time.
The Long-Run Aggregate Supply Curve: Vertical by Design
The Long-Run Aggregate Supply (LAS) curve is vertical at the economy's full-employment output level. This means real GDP doesn't change when the price level changes—only potential GDP matters in the long run.
Why is it vertical? Because in the long run:
- Wages and prices adjust fully to changes in the price level
- Resources get fully utilized
- The economy produces at its maximum sustainable capacity
- No "sticky" prices or wages exist
The LAS curve shifts right over time as the economy grows—more workers, better technology, more capital. But within any given time period, it's fixed at one output level.
Why the LRPC and LAS Are the Same Thing
Here's what textbooks often bury: the LRPC is just the LRAS curve in different clothing. Both show:
- A fixed output level determined by real factors (technology, resources, productivity)
- No response to price level changes
- Monetary policy unable to shift the curve
The vertical line on the Phillips Curve diagram (inflation vs. unemployment) corresponds exactly to the vertical line on the Aggregate Supply diagram (price level vs. real GDP). The only difference is which variables sit on the axes.
Short-Run vs. Long-Run: The Real Difference
In the short run, the SRAS curve slopes upward and the SRPC shows a tradeoff. Businesses and workers can be fooled by unexpected price changes. They think their prices or wages are rising when actually everything is rising together.
In the long run, everyone adjusts. Workers realize their real wages haven't changed. Businesses see costs rising with prices. The illusion disappears, and the economy snaps back to natural unemployment and potential GDP.
Factors That Actually Shift the LRAS and LRPC
These are the only things that can shift the long-run curves:
- Changes in the labor force — more workers means higher potential output
- Changes in capital stock — investment shifts the curve right, depreciation shifts it left
- Technological progress — the biggest driver of long-run growth
- Resource discoveries or depletions — oil finds right the curve; drought shifts it left
- Institutional changes — education quality, labor market regulations, trade policies
Monetary policy, government spending, and tax changes cannot shift the LRAS or LRPC. They only move the economy along these curves in the short run.
Comparing SRAS, LRAS, SRPC, and LRPC
| Curve | Shape | What It Shows | Shifted By |
|---|---|---|---|
| SRAS | Upward sloping | Short-run price-output relationship | Input costs, expectations, supply shocks |
| LRAS | Vertical | Potential GDP (independent of price level) | Real factors: technology, resources, labor force |
| SRPC | Downward sloping | Short-run inflation-unemployment tradeoff | Expected inflation, supply shocks |
| LRPC | Vertical | Natural rate of unemployment | Same as LRAS: real factors only |
Getting Started: How to Analyze LRPC and LRAS Problems
When you face an economics problem involving these curves, follow this process:
Step 1: Identify the Time Horizon
Ask yourself: short run or long run? If the question mentions "long run," "eventually," or "in the long term," you're working with vertical curves. If it says "initially," "temporarily," or "in the short run," expect movement along the curves.
Step 2: Classify the Shock
Is it a demand-side shock or supply-side shock?
- Demand shocks (consumer spending, exports, money supply) move the economy along existing curves initially
- Supply shocks (oil prices, technology, natural disasters) shift the curves themselves
Step 3: Draw and Label
Start with LRAS/LRPC as a vertical line at the natural rate. Add SRAS/SRPC as an upward or downward sloping curve intersecting at equilibrium. Show the shock, then trace where the economy settles.
Step 4: Find the New Equilibrium
In the long run, the economy returns to the vertical LRAS and LRPC. The price level or inflation rate may be higher or lower, but output and unemployment return to their natural rates.
The Policy Takeaway
Policymakers who try to permanently lower unemployment below the natural rate through stimulus spending or money printing will only generate inflation. The LRPC makes this clear: you can fool people temporarily, but the economy always returns to its natural unemployment rate.
If you want to lower the natural rate of unemployment, you need real changes—better education, labor market reforms, technology investment. Not more money printing.