AP Syllabus focus: ‘An outward shift in the production possibilities curve is analogous to a rightward shift of the long-run aggregate supply curve.’
These notes connect two core long-run growth visuals: the production possibilities curve (PPC) and long-run aggregate supply (LRAS). Both show changes in an economy’s capacity to produce, rather than short-run fluctuations.
Core Idea: Productive Capacity and Long-Run Growth
Long-run economic growth means the economy can produce more real output over time. In AP Macroeconomics, a rise in capacity is shown in two parallel ways:
An outward shift of the PPC (more possible output combinations)
A rightward shift of LRAS (higher potential output / full-employment output)
These are “analogous” because each represents an expansion in the economy’s ability to produce goods and services with available resources and technology.
The PPC View of Long-Run Growth
The PPC is a real-side (resource/technology) model of capacity.
PPC (Production Possibilities Curve): A curve showing the maximum combinations of two goods/services an economy can produce using existing resources and technology efficiently.
An outward PPC shift means the economy can produce more of both categories than before (for example, more consumer goods and more capital goods).
This PPC diagram contrasts the original production possibilities curve with an outward-shifted curve after economic growth. The outward shift shows that combinations previously outside the frontier become attainable, illustrating an increase in the economy’s productive capacity. Source
Key interpretations:
More resources (larger labour force, more natural resources) expand feasible production.
Better technology or productivity allows more output from the same inputs.
More capital accumulation increases future production capacity, often shifting the PPC outward more strongly over time.
Why “Outward” Means Growth
Outward shifts represent:
Higher maximum real output possibilities
Greater long-run living standards potential (more goods and services per person)
A larger capacity to produce without sacrificing efficiency
The LRAS View of Long-Run Growth
LRAS focuses on macroeconomy-wide productive capacity at full employment.
LRAS (Long-Run Aggregate Supply): The vertical aggregate supply curve showing the level of real output produced at full employment (potential output), which is determined by resources, technology, and institutions—not the price level.
Because LRAS is vertical, a rightward shift is not “more output because prices changed”; it is more output because capacity increased.
This graph depicts the long-run aggregate supply curve (LRAS) as vertical at full-employment (potential) output, emphasizing that the price level does not change long-run real output. A rightward shift in LRAS represents higher potential real GDP caused by changes in long-run determinants like technology or factor inputs. Source
“Rightward LRAS Shift” as Long-Run Growth
A rightward shift of LRAS indicates:
Higher potential output (the full-employment level of real GDP rises)
The economy can sustain a higher level of production without creating ongoing inflationary pressure from capacity limits
Why PPC Shifts and LRAS Shifts Are Analogous
Both models describe changes in the economy’s maximum sustainable real output:
PPC: maximum feasible combinations across categories of output
LRAS: maximum feasible total real output at full employment
A useful way to link them:
If the PPC shifts outward, the economy’s overall production frontier expands.
That same expansion implies the economy’s potential real GDP is higher.
Higher potential real GDP is exactly what a rightward LRAS shift represents.
What This Analogy Helps You Do on AP Graphs
When you see evidence of long-run growth (capacity rising), you should be able to state consistently:
PPC shifts outward
LRAS shifts right
Potential output increases
Important Clarifications (Common AP Pitfalls)
Capacity growth vs. short-run changes
PPC/LRAS shifts are about long-run capacity, not temporary demand-driven changes.
A rise in AD can raise real GDP in the short run, but it does not shift PPC or LRAS by itself.
Inward shifts mean shrinking capacity
The same logic runs in reverse:
An inward shift of the PPC is analogous to a leftward shift of LRAS.
This indicates reduced productive capacity (lower potential output), which can occur due to long-lasting resource loss or institutional breakdown.
“More output” must be feasible and sustainable
Long-run growth requires changes that increase what the economy can produce at full employment, not just what it happens to produce during a boom.
FAQ
No. LRAS can shift right if overall capacity rises, even if the PPC shifts more towards one type of output (e.g., capital-goods-heavy growth).
LRAS being vertical means potential output is independent of the price level at a point in time. PPC/LRAS shifts occur when resources/technology change, not because prices change.
Yes. Better utilisation (lower unemployment/inefficiency) moves the economy towards the frontier, but capacity (the frontier itself) is unchanged, so LRAS does not shift.
Persistent losses such as:
Destruction of physical capital
Long-term population decline
Sustained deterioration in institutions or productivity
Investment that adds to the capital stock tends to expand future capacity. Over time this can push the PPC outward and shift LRAS right by raising potential output.
Practice Questions
(2 marks) Explain why an outward shift in the PPC is analogous to a rightward shift in LRAS.
1 mark: Outward PPC shift indicates increased productive capacity / ability to produce more goods and services.
1 mark: Rightward LRAS shift indicates higher potential output (full-employment real GDP), also reflecting increased productive capacity.
(6 marks) Describe two distinct changes that could cause long-run economic growth and explain how each would be shown on both a PPC and an LRAS graph.
1 mark: Identifies a valid cause 1 (e.g., technological improvement, more capital, larger workforce).
1 mark: Explains cause 1 increases productive capacity.
1 mark: Shows cause 1 shifts PPC outward.
1 mark: Shows cause 1 shifts LRAS right (higher potential output).
1 mark: Identifies a valid cause 2 (distinct from cause 1).
1 mark: Correctly links cause 2 to outward PPC and rightward LRAS via higher capacity/potential output.
