Aggregate supply completes the AD-AS model at the core of "National Income and Price Determination" (15%–20% of the CLEP exam). One of the official sample questions asks directly: "Which of the following will cause the short-run aggregate supply curve to shift to the right?" — the shifter lists in this lesson are exam currency.
Short-run aggregate supply (SRAS) shows the total output firms produce at each price level during the period when input prices — especially wages — are fixed or sticky. That stickiness defines the macroeconomic short run: output prices can move while input costs lag behind, because wages are locked into contracts and renegotiated slowly.
Why SRAS slopes upward. Suppose the price level rises while wages are stuck at last year's contract:
Higher PL → more output supplied: an upward slope. And as always, a price-level change is a movement along SRAS — never a shift.
Anything that changes production costs or productivity at every price level shifts the whole curve. Rightward = producing any given output got cheaper; leftward = costlier.
| Shifter | SRAS right (costs ↓) | SRAS left (costs ↑) |
|---|---|---|
| Input/resource prices (wages, energy, raw materials) | Oil prices fall; wages fall | Oil spike; economy-wide wage increases |
| Productivity/technology | Better technology → more output per input | Productivity collapse |
| Per-unit taxes, subsidies, regulation | Subsidies; deregulation; per-unit tax cuts | New per-unit production taxes; costly compliance rules |
| Inflation expectations | Expected inflation falls → moderate wage demands | Expected inflation rises → workers demand higher wages now |
| Supply shocks | Positive (bumper harvest) | Negative (war, embargo, disaster, pandemic) |
Expectations deserve emphasis: if everyone expects 6% inflation, wage bargains build it in, costs rise, and SRAS shifts left with no real shock at all.
[GRAPH: Short-Run Aggregate Supply
X-axis: Real GDP (Y)
Y-axis: Price level (PL)
Curve 1: SRAS, upward-sloping, labeled SRAS₁
Reading: PL rises from 100 to 105 with wages fixed → profit margins widen →
output supplied rises — a movement ALONG SRAS₁
Shift: world oil prices double → production costs rise at EVERY price level →
SRAS shifts LEFT to SRAS₂ → at any given PL, less output supplied]
A negative supply shock (SRAS left, along a fixed AD) raises the price level while cutting output — inflation plus recession at once: stagflation. The 1970s oil embargoes are the canonical case: energy costs exploded, and the economy delivered rising prices and rising unemployment simultaneously. No demand-side story can produce that combination — AD shifts move prices and output in the same direction. When a question pairs falling output with a rising price level, the answer is a leftward SRAS shift.
Stagflation also puts demand policy in a bind: stimulate spending and inflation worsens; fight inflation and the recession deepens. Recognizing "supply shock, not demand slump" is the high-value diagnostic skill.
[GRAPH: Negative supply shock (stagflation)
X-axis: Real GDP (Y)
Y-axis: Price level (PL)
Curve 1: AD, downward-sloping, fixed
Curve 2: SRAS₁ shifting left to SRAS₂
Equilibrium: moves from (Y₁, PL₁) up-left to (Y₂ < Y₁, PL₂ > PL₁)
Effect: output falls AND the price level rises — stagflation]
In the long run, all prices — including wages — are fully flexible. If the price level doubles and wages double with it, no firm has any profit reason to change output. The price level therefore has no effect on long-run production:
LRAS is vertical at full-employment output (Yf) — potential output, the level where unemployment sits at its natural rate (Lesson 4). The economy can operate left of it (recession) or briefly right of it (overtime, delayed maintenance, workers drawn in), but Yf is set by real capacity.
LRAS shifts only with real productive capacity:
| LRAS right (potential output grows) | Does NOT shift LRAS |
|---|---|
| More resources: labor force growth, capital accumulation | The price level |
| Better technology and productivity | The money supply |
| Improved institutions, education, infrastructure | Consumer confidence, government stimulus, or any purely nominal or demand-side change |
Demand does not build factories. Anything that shifts LRAS also shifts SRAS the same direction (more capacity means more output at every price level), but the reverse is not true: a wage change moves SRAS alone, leaving potential output untouched.
1. E. Sticky input costs plus rising output prices mean fatter margins, so firms produce more — the core short-run mechanism. A: the wealth effect explains AD's slope, not SRAS's. B: the money supply is set by the central bank, not by the price level. C: if input prices adjusted instantly, SRAS would be vertical — stickiness is the whole point. D: full-capacity production would make supply unresponsive, not upward-sloping.
Fix: SRAS slopes up because output prices outrun sticky input prices in the short run.
2. B. With full wage-and-price flexibility, the price level and costs move together, so no price level induces more or less output — only real factors set production. A: the long run frees the price level; it does not fix it. C: demand determines long-run prices, not long-run output. D: the money supply has nothing to do with LRAS's shape. E: the long run is precisely when firms can change everything.
Fix: Vertical LRAS = in the long run, output is a real phenomenon, not a nominal one.
3. E. The price level is the vertical-axis variable: its changes slide the economy along SRAS. A: wages are the dominant input price — a shifter. B: energy costs are a shifter. C: per-unit taxes change unit costs — a shifter. D: technology changes capability — a shifter.
Fix: Only the price level moves you along SRAS; costs and capability move the curve.
4. A. Energy is a near-universal input; doubled costs mean less is supplied at every price level → SRAS left. B: conservation cannot reverse an economy-wide cost explosion. C: imported inputs still enter domestic production costs. D: cost shocks shift the curve; they do not change its shape. E: producer revenues do not lower anyone's unit production costs.
Fix: Input-price shocks — oil above all — shift SRAS opposite to the direction of the cost change.
5. C. More output per worker = lower per-unit cost = SRAS right. A: productivity gains expand supply even where labor is displaced. B: productivity shifts both SRAS and LRAS. D: shifters relocate the curve; they do not steepen it. E: no wage increase is described — that is an imported assumption.
Fix: Productivity up → unit costs down → SRAS (and LRAS) right.
6. D. Expected inflation flows into today's wage bargains → higher current costs → SRAS left, before any actual inflation appears. A: inflation expectations, if anything, accelerate purchases — and the tested channel is costs. B: no actual price-level change has occurred yet. C: backwards — expectations raise costs; they don't expand supply. E: expectations act through current contracts; there is no waiting period.
Fix: Inflation expectations are a cost shifter — they move SRAS left ahead of the inflation itself.
7. C. Only SRAS-left produces the up-left combination: price level rises while output falls. A: AD right raises both. B: AD left lowers both. D: SRAS right is the favorable opposite — output up, prices down. E: a movement along a curve cannot change equilibrium by itself.
Fix: Opposite moves in PL and output = supply story; same-direction moves = demand story.
8. E. Cutting per-unit production taxes lowers unit costs at every price level → SRAS right. A: a higher minimum wage raises labor costs → left. B: a per-unit output tax raises unit costs → left. C: transfers work on AD through consumption, not on production costs. D: costlier compliance raises unit costs → left.
Fix: For SRAS, follow per-unit production costs — down = right, up = left.
9. B. Falling output prices against contract-fixed wages squeeze profit margins → firms cut output: the downward movement along SRAS. A: real wages rose (same nominal wage, lower prices) — labor became costlier, not cheaper. C: nothing shifted; the price level moved. D: raising wages in a margin squeeze compounds the problem and is not the modeled response. E: the whole point of stickiness is that effects hit before contracts expire.
Fix: Deflation with sticky wages = margin squeeze = slide down along SRAS.
10. A. A permanently larger labor force is more productive capacity: LRAS shifts right, and SRAS shifts right with it (more labor at every price level). B: LRAS does move — resources changed. C: capacity, not just prices, changes. D: labor force growth is a supply-side event, not a spending event. E: capital dilution is not how the model treats resource growth — more labor raises potential output.
Fix: Resource growth moves both supply curves right; potential output rises.
11. A. Potential output is set by real factors — labor, capital, technology, institutions. Money is nominal; printing it builds no factories. B: more money shifts AD and ultimately the price level, not capacity. C: there is no lagged LRAS effect from money in this model. D: money does not shift LRAS in either direction. E: LRAS certainly can shift — through real factors like technology and resource growth.
Fix: LRAS shifters are real, never nominal: resources, capital, technology — not money, prices, or confidence.
12. D. Cost changes relocate the entire SRAS curve; the resulting equilibrium price-level change is an outcome of the shift, not a movement along the original curve. A: reverses cause and effect. B: production costs belong to the supply side, not to AD. C: the shift logic applies to any economy-wide cost change, not just energy. E: shifts move curves in parallel; rotation to vertical is not a mechanism here.
Fix: Identify what initiated the change — the price level (movement along) or costs (shift) — and never let a shift masquerade as a movement.
1. E. Sticky input costs plus rising output prices mean fatter margins, so firms produce more — the core short-run mechanism. A: the wealth effect explains AD's slope, not SRAS's. B: the money supply is set by the central bank, not by the price level. C: if input prices adjusted instantly, SRAS would be vertical — stickiness is the whole point. D: full-capacity production would make supply unresponsive, not upward-sloping. Fix: SRAS slopes up because output prices outrun sticky input prices in the short run.
2. B. With full wage-and-price flexibility, the price level and costs move together, so no price level induces more or less output — only real factors set production. A: the long run frees the price level; it does not fix it. C: demand determines long-run prices, not long-run output. D: the money supply has nothing to do with LRAS's shape. E: the long run is precisely when firms can change everything. Fix: Vertical LRAS = in the long run, output is a real phenomenon, not a nominal one.
3. E. The price level is the vertical-axis variable: its changes slide the economy along SRAS. A: wages are the dominant input price — a shifter. B: energy costs are a shifter. C: per-unit taxes change unit costs — a shifter. D: technology changes capability — a shifter. Fix: Only the price level moves you along SRAS; costs and capability move the curve.
4. A. Energy is a near-universal input; doubled costs mean less is supplied at every price level → SRAS left. B: conservation cannot reverse an economy-wide cost explosion. C: imported inputs still enter domestic production costs. D: cost shocks shift the curve; they do not change its shape. E: producer revenues do not lower anyone's unit production costs. Fix: Input-price shocks — oil above all — shift SRAS opposite to the direction of the cost change.
5. C. More output per worker = lower per-unit cost = SRAS right. A: productivity gains expand supply even where labor is displaced. B: productivity shifts both SRAS and LRAS. D: shifters relocate the curve; they do not steepen it. E: no wage increase is described — that is an imported assumption. Fix: Productivity up → unit costs down → SRAS (and LRAS) right.
6. D. Expected inflation flows into today's wage bargains → higher current costs → SRAS left, before any actual inflation appears. A: inflation expectations, if anything, accelerate purchases — and the tested channel is costs. B: no actual price-level change has occurred yet. C: backwards — expectations raise costs; they don't expand supply. E: expectations act through current contracts; there is no waiting period. Fix: Inflation expectations are a cost shifter — they move SRAS left ahead of the inflation itself.
7. C. Only SRAS-left produces the up-left combination: price level rises while output falls. A: AD right raises both. B: AD left lowers both. D: SRAS right is the favorable opposite — output up, prices down. E: a movement along a curve cannot change equilibrium by itself. Fix: Opposite moves in PL and output = supply story; same-direction moves = demand story.
8. E. Cutting per-unit production taxes lowers unit costs at every price level → SRAS right. A: a higher minimum wage raises labor costs → left. B: a per-unit output tax raises unit costs → left. C: transfers work on AD through consumption, not on production costs. D: costlier compliance raises unit costs → left. Fix: For SRAS, follow per-unit production costs — down = right, up = left.
9. B. Falling output prices against contract-fixed wages squeeze profit margins → firms cut output: the downward movement along SRAS. A: real wages rose (same nominal wage, lower prices) — labor became costlier, not cheaper. C: nothing shifted; the price level moved. D: raising wages in a margin squeeze compounds the problem and is not the modeled response. E: the whole point of stickiness is that effects hit before contracts expire. Fix: Deflation with sticky wages = margin squeeze = slide down along SRAS.
10. A. A permanently larger labor force is more productive capacity: LRAS shifts right, and SRAS shifts right with it (more labor at every price level). B: LRAS does move — resources changed. C: capacity, not just prices, changes. D: labor force growth is a supply-side event, not a spending event. E: capital dilution is not how the model treats resource growth — more labor raises potential output. Fix: Resource growth moves both supply curves right; potential output rises.
11. A. Potential output is set by real factors — labor, capital, technology, institutions. Money is nominal; printing it builds no factories. B: more money shifts AD and ultimately the price level, not capacity. C: there is no lagged LRAS effect from money in this model. D: money does not shift LRAS in either direction. E: LRAS certainly can shift — through real factors like technology and resource growth. Fix: LRAS shifters are real, never nominal: resources, capital, technology — not money, prices, or confidence.
12. D. Cost changes relocate the entire SRAS curve; the resulting equilibrium price-level change is an outcome of the shift, not a movement along the original curve. A: reverses cause and effect. B: production costs belong to the supply side, not to AD. C: the shift logic applies to any economy-wide cost change, not just energy. E: shifts move curves in parallel; rotation to vertical is not a mechanism here. Fix: Identify what initiated the change — the price level (movement along) or costs (shift) — and never let a shift masquerade as a movement.