Chapter 11 · Macroeconomic objectives II: Economic growth, sustainable level of debt
Economic growth using the PPC
Distinguish actual growth from potential growth using a PPC. Compare using unemployed resources with expanding the economy’s productive capacity.
The economic idea
Economic growth is an increase in real output over time. Actual economic growth occurs when currently produced output rises, including movement from inside a PPC toward the existing frontier. Potential economic growth occurs when productive capacity increases and the PPC shifts outward.
A point on a PPC is productively efficient because the economy is using available resources fully to produce the maximum feasible combination. A point inside is attainable but productively inefficient because resources are unemployed or misallocated. A point beyond the PPC is currently unattainable.
The PPC is normally bowed outward because resources are specialised, creating increasing opportunity cost as production is reallocated. A shift can be balanced or biased toward one good, depending on which resources or technologies improve.
Producing more capital goods can require sacrificing current consumer goods but may expand future capacity. If the investment is financed by public borrowing, sustainability depends on its return relative to financing costs and on the government’s wider fiscal position; the PPC itself does not display debt.
Reading A₁ and A₂ against PPC₁ and PPC₂
“Good X” is measured on the horizontal axis and “Good Y” on the vertical axis. Every point represents a combination of the two output categories.
“PPC₂” is the current production boundary and “PPC₁” preserves the earlier boundary.
“A₂” is the current output combination and “A₁” is the earlier combination. A point and a frontier answer different questions: utilisation versus capacity.
What happened to productive capacity?
“PPC₂” lies outside “PPC₁”. The economy can produce more of at least one good without sacrificing its previous maximum of the other, so productive capacity has increased and the graph shows potential economic growth.
What happened to actual resource use?
“A₁” records production relative to “PPC₁”, while “A₂” records production relative to “PPC₂”. The frontier shift establishes the capacity change; the points show how much of each frontier is being used.
What the slope still means
Moving along either frontier reallocates resources between “Good X” and “Good Y”. The absolute slope is the opportunity cost of additional “Good X” in terms of forgone “Good Y”; it is not an economic growth rate.
Distinguish capacity, resource use and consumption
A movement from inside a PPC towards it uses existing capacity more fully. An outward shift means more combinations can be produced with the resources and technology available. Moving along the same frontier changes the mix of output and involves an opportunity cost.
Trade may allow consumption beyond a country’s own PPC, but it does not allow that country to produce beyond its current frontier. Keep production possibilities separate from consumption possibilities when applying this model.
From resource use and investment to the displayed growth state
Use the allocation points first: “A₁” and “A₂” reveal whether more of the available capacity is being used.
Use the frontiers separately: “PPC₁” and “PPC₂” reveal whether maximum attainable output has changed.
Common mistakes to avoid
- Movement from inside a PPC to the same frontier is actual growth, not an increase in productive capacity.
- Movement along a PPC is reallocation and opportunity cost, not economic growth by itself.
- An outward shift raises possibilities but does not guarantee that the economy will operate on the new frontier.
- A pivot toward one axis is biased growth and does not necessarily permit more of both goods.
- The graph contains no debt stock, interest rate or fiscal balance and cannot prove debt sustainability.
How to draw this diagram
- Title the diagram “Economic growth using the PPC”. Label the horizontal axis “Good X” and the vertical axis “Good Y”.
- Draw PPC₂ first and label it clearly.
- Draw PPC₁ next and label it clearly.
- Mark each relevant intersection and distinguish the initial, market and socially optimum or policy outcomes where applicable.
- Add the relevant guide lines and shade the economic area only after its boundaries are established.
- Check that every symbol used in the explanation appears on the diagram and add arrows showing the direction of change.
Assumptions and limitations
- A two-good model compresses a diverse economy into two broad output categories.
- The PPC does not show prices, aggregate demand, income distribution or which combination maximises welfare.
- The frontier is not directly observable and investment may take years to affect capacity.
- Growth may be resource-intensive or environmentally unsustainable even when the curve shifts outward.
- The model cannot identify how investment was financed or whether debt can be serviced.