Aggregate Supply vs Long-Run Aggregate Supply
Aggregate Supply and Long-Run Aggregate Supply are two Aggregate Demand & Supply concepts in AP Economics that students often mix up. Aggregate supply is the total supply of final goods and services in an economy at a given time. Long-run aggregate supply is the total supply of goods and services when all factors of production are fully employed. Here is how they compare side by side.
Aggregate supply represents the total amount of goods and services that firms plan to produce and sell at a given price level. In the short run, aggregate supply can increase or decrease with changes in the price level. In the long run, aggregate supply is determined by an economy's factors of production.
In the long run, an economy's potential output is determined by its factors of production, such as labor, capital, and technology. Changes in the price level do not affect the quantity of goods and services supplied in the long run. The LRAS curve is vertical.
Aggregate Supply vs LRAS: What Firms Choose to Produce and What the Economy Can Produce
| Aggregate Supply | Long-Run Aggregate Supply | |
|---|---|---|
| The question it answers | How much firms choose to offer at each price level | How much the economy can produce with every resource in use |
| Sensitivity to the price level | Positive in the short run, because wider margins pull output up | Zero, which is exactly why the curve is drawn vertical |
| Moved by a jump in input prices | Yes, the short-run curve shifts left | No, since a larger cost bill destroys no resources |
| Moved by more workers, more capital or better technology | Yes | Yes, and this is the only class of change that moves it |
| How long a shift lasts | Until input prices and expectations catch up | Indefinitely, because capacity itself has changed |
| Can the economy sit off it | No, since the curve is defined by what firms are actually doing | Yes, and the distance from it is the output gap |
| Other names for the same idea | The supply side of the model | Potential output, full-employment output, the level behind a point on the production possibilities curve |
One curve describes a choice, the other describes a limit
Short-run aggregate supply is behavioral. It says that when the price level rises while input prices lag behind, each extra unit is more profitable, so firms choose to make more. Long-run aggregate supply is not a behavioral response at all. It counts what the economy has to work with: workers, capital, land, technology and the institutions that put them to use. No price appears anywhere in that count, which is why the curve is vertical, and it is also why the phrase an increase in aggregate supply is ambiguous. A fall in the cost of imported components makes production cheaper, firms offer more at every price level, and the short-run curve moves right, yet nothing about the workforce or the capital stock has changed, so the limit has not moved at all. A rule about position follows. The economy always sits somewhere on its short-run curve, because that curve is defined by what firms are doing right now. The economy does not have to sit on the long-run line, and the distance between the two is the output gap. Deciding which curve a question is about therefore decides whether you are describing a temporary state or a permanent one.
Two shocks look identical for a year, then the policy answer flips
Take two economies, each with potential output of 900 units. In the first, a drought raises the cost of agricultural inputs. Short-run aggregate supply shifts left, the new intersection lands at 860 units while the price index climbs from 100 to 105, and long-run aggregate supply is still standing at 900. The economy sits 40 units below potential, unemployment is above its natural rate, and there is a real recessionary gap. In the second economy, part of the capital stock is destroyed and never rebuilt. Both supply curves move left together, output settles at 860 with a higher price level, and potential output is now 860 as well. The two economies report the same drop in output and the same rise in prices, and the correct policy answer is opposite. The first has a gap that closes on its own once input costs come back down, and expansionary policy can close it sooner. The second has no gap at all, so demand-side policy would push spending against a capacity that no longer exists and almost all of it would land on the price level. That is why prompts describe shocks so precisely. A bad harvest, a strike or an energy spike is temporary and moves one curve. Emigration, a shrinking workforce or destroyed capital is permanent and moves both.
Frequently asked questions
Is aggregate supply the same as long-run aggregate supply?
Aggregate supply covers both supply curves in the AD-AS model, and long-run aggregate supply is only one of them, the vertical line drawn at potential output. An unqualified reference to aggregate supply usually means the upward sloping short-run curve, since the familiar shifters are production costs. Long-run aggregate supply is the curve a growth question is about, because it moves only when resources, technology or institutions change.
Can real GDP be higher than long-run aggregate supply?
Real GDP can sit above long-run aggregate supply for a stretch, and that situation is an inflationary gap. Potential output is the level produced when unemployment is at its natural rate rather than a physical ceiling, so overtime, extra shifts and unusually low unemployment can push production past it. The state does not last, because a tight labor market raises wages, short-run aggregate supply shifts left, and output returns to the line at a higher price level.
What does aggregate supply mean in a question about economic growth?
Aggregate supply in a growth question means productive capacity, so the curve being shifted is the long-run one and a good answer names resources, capital, technology or institutions. Cheaper energy or a weaker currency changes costs rather than capacity, which moves the short-run curve only and produces no growth in the sense the question wants. Growth on this diagram is the vertical line moving right, which is worked through at /macro/economic-growth.
Live AD/AS Model graph. Drag the curves, or open the full version.
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