Short-Run Aggregate Supply

Section 3.1 covered Aggregate Demand — how much output all the buyers in an economy want to purchase at each price level. But demand is only half the story. To know what the economy actually produces, we also need to ask: how much are producers willing to supply? That's the question Aggregate Supply answers.

Here's where it gets interesting: there are two aggregate supply curves, not one. In the short run, some things in the economy can't adjust quickly — wages are locked into contracts, rents are fixed for the year, raw material orders are already placed. When the price level changes, producers face a temporary mismatch: revenues move but many costs don't. That mismatch creates the upward-sloping Short-Run Aggregate Supply (SRAS) curve we'll meet in this section.

In the long run, every price is flexible — workers renegotiate, contracts expire, all costs catch up. Producers can no longer gain from price-cost mismatches, and supply behaves completely differently. That's Long-Run Aggregate Supply (LRAS), which we'll tackle in Section 3.3.

For now, focus on the short run. The key concept is sticky wages — the idea that the price level can change faster than wages can. Once you understand sticky wages, every part of SRAS clicks into place: why it slopes upward, what shifts it, and why supply shocks are so painful for the economy.

Short-Run Aggregate Supply tells us how much total output producers across the entire economy are willing and able to produce at each price level — when some input costs (especially wages) can't adjust right away.

What "Sticky" Actually Means

Wages and many other input costs don't move freely from minute to minute the way stock prices do. Workers sign labor contracts that lock in their wage for a year or more. Suppliers negotiate raw material contracts months in advance. Commercial leases run for years. All of these arrangements create a lag between when the overall price level changes and when input costs catch up.

"Sticky" is the technical term for this lag. The price level can rise tomorrow, but if your factory workers have a three-year contract at $25/hour, you're still paying $25/hour for the rest of that contract — regardless of what's happening to bread prices, gas prices, or anything else. That stickiness is the engine of everything in this section.

The SRAS curve slopes upward — at a higher price level, producers want to supply more; at a lower price level, they want to supply less. The reason is straightforward once you see it with a concrete example.

The Key Insight

The upward slope of SRAS depends entirely on input costs being slow to adjust. If wages and other costs could rise instantly along with the price level, profit margins wouldn't change, and firms wouldn't have any reason to produce more or less. That's exactly what happens in the long run (Section 3.3) — and it's why LRAS is vertical instead of upward-sloping.

So remember: SRAS slopes up because the short run is the period when costs are sticky. The shape of the curve is a direct consequence of that single fact.

Just like with AD, you have to distinguish between movement along SRAS and shifts of SRAS. The logic is exactly the same — if the trigger is the price level, it's movement along; if the trigger is anything else, it's a shift.

The Visual Difference

The shifters of SRAS all share a common feature: they change the cost of producing output, or the productivity of producing it, at every price level. There are four main categories. Master each one and the direction of the shift becomes automatic.

Putting It All Together

One scenario deserves its own discussion because it shows up on almost every AP exam: the negative supply shock. When SRAS shifts sharply left — usually because of an oil price spike, natural disaster, or war — something unusual happens. The economy gets hit with two bad outcomes simultaneously.

The Mechanics

Normally, prices and output move together — both rise in a boom (AD shift right) and both fall in a recession (AD shift left). But a leftward SRAS shift breaks that pattern:

Why Stagflation Is So Hard to Fix

This is where policy gets miserable. Normally, when the economy is in trouble, the government has clear tools:

• Recession (low output, low prices)? Boost AD with expansionary fiscal or monetary policy. Both output and prices rise. Problem solved.
• Overheating (high output, high prices)? Cool AD with contractionary policy. Both output and prices fall. Problem solved.
• Stagflation (low output AND high prices)?  ... uh-oh.

If policymakers boost AD to fight the recession, they make inflation worse. If they tighten to fight inflation, they deepen the recession. There's no AD-side answer that fixes both problems simultaneously. The only real cure is to wait for SRAS to shift back to the right — or to invest in the supply side directly (productivity improvements, deregulation), which takes time.

This is why the 1970s oil shocks were such a nightmare. The U.S. economy had double-digit inflation and rising unemployment. Standard demand-management tools couldn't address both, and the period became the textbook case for the supply-shock-induced stagflation that AP exams love to test.

• "SRAS slopes upward because higher prices encourage more supply, like in micro." Sort of — but the precise reason matters. In micro, individual firms supply more at higher prices because they can earn more revenue. In macro, the SRAS slope depends specifically on sticky wages and input costs: higher PL with fixed costs means bigger margins per unit. If you describe the slope without mentioning sticky costs, you'll lose points on the FRQ.
• "Higher input prices shift SRAS right because firms charge more." Wrong direction. Higher input prices raise costs, which squeezes profit margins at every selling price → less output → SRAS shifts left. The "charge more" intuition is misleading because firms can't always pass higher costs onto consumers, and even when they can, output still falls.
• "A price-level change shifts SRAS." No — that's movement along. A change in the price level triggers the sticky-wage mechanism but doesn't relocate the curve. Shifts come from changes in costs, productivity, expectations, or shocks.
• "Stagflation is just a really bad recession." No. A recession is falling output with falling prices (AD shifts left). Stagflation is falling output with rising prices — a totally different combination caused by a leftward SRAS shift, not by AD weakness.
• "Wages are always sticky." Sticky in the short run, flexible in the long run. The whole distinction between SRAS (upward-sloping) and LRAS (vertical, coming in 3.3) depends on this contrast. Don't apply short-run logic to long-run questions.
• "Inflationary expectations only affect AD." Inflationary expectations are major SRAS shifters too. When workers expect higher inflation, they demand higher wages now — which raises costs and shifts SRAS left. This is the engine of long-run self-correction that we'll see in 3.4.
• "Government regulation can only shift SRAS left." Costly regulations shift SRAS left, but deregulation or subsidies shift it right. Government policy is bidirectional — pay attention to the specific policy described.