Step 2: The Production Possibility Curve
- The Production Possibility Curve (PPC) shows the maximum combinations of two goods an economy can produce when all its resources are used fully and efficiently.
- Points on the curve are efficient, points inside are inefficient (idle resources), and points outside cannot be reached yet.
- Opportunity cost on the PPC is the slope: \( \text{OC of } X = \Delta Y \div \Delta X \). Most PPCs bow outward because opportunity cost rises as you produce more of one good.
- Exam point: growth is an outward shift of the curve. Falling unemployment is a movement from inside the curve towards it, not a shift.
What the PPC shows: a menu of what is possible
Picture a small bakery with two ovens, three bakers and a fixed amount of flour each day. If it makes only bread, it might bake 200 loaves. If it makes only cakes, perhaps 50 cakes. Most days it makes some of each. Every possible mix it could make, using everything it has, forms a menu. Draw that menu on a graph and you have a Production Possibility Curve.
Now scale this up to a whole country that makes two goods, say smartphones and bicycles. Each point on its PPC is one combination it could produce if all its resources were used fully and efficiently. The curve is the boundary between what is possible and what is not.
The PPC rests on four assumptions. Learn them, because exam questions test what happens when one is relaxed:
- Only two goods are produced. This simplification lets us draw the curve in two dimensions.
- Resources are fixed in quantity. We look at one moment in time.
- Technology is given. No new production methods appear.
- All resources are used fully and efficiently: no unemployment, no idle factories, no waste.
Reading the curve: on, inside and outside
A typical exam PPC puts capital goods (machines, factories) on the vertical axis and consumer goods (food, clothes, phones) on the horizontal axis. Suppose the curve passes through (30 consumer, 70 capital) and (70 consumer, 30 capital).
| Point | Position | What it means |
|---|---|---|
| A: 30 consumer, 70 capital | On the curve | Efficient. The mix favours investment in the future. |
| B: 70 consumer, 30 capital | On the curve | Also efficient. The mix favours current living standards. |
| C: 30 of each | Inside the curve | Inefficient. Some workers are unemployed or some factories are idle. |
| D: 80 of each | Outside the curve | Unattainable with today’s resources and technology. |
A and B are both efficient; the difference is a choice of priorities, not of ability. A point like C is what a recession looks like: the 2008 financial crisis and the start of COVID-19 pushed many economies inside their curves. The only way to reach D is for the curve itself to move outward.
Opportunity cost is the slope
You met opportunity cost in Step 1. The PPC lets you see it. Moving from A (70 capital, 30 consumer) to B (30 capital, 70 consumer), the economy gains 40 consumer goods and gives up 40 capital goods. So each extra consumer good costs one capital good.
Two things to notice. First, opportunity cost is measured in units of the other good, not in money; on a PPC, dollars do not exist. Second, opportunity cost equals the slope of the curve. A steep section means a high opportunity cost: you give up a lot of Y for a little more X. A flat section means a low one.
An economy’s PPC passes through these points: P (0 consumer, 100 capital), Q (20, 95), R (40, 80), S (60, 50) and T (80, 0). Find the opportunity cost of one consumer good for each move along the curve.
The opportunity cost rises from 0.25 to 0.75 to 1.5 to 2.5. Each extra batch of consumer goods costs more capital goods than the one before. That is why this curve bows outward.
Why most PPCs bow outward
A bowed-out PPC is called concave. The shape comes from a simple fact: resources are not equally good at everything. Some workers, machines and land suit capital goods (engineers, heavy machinery, industrial land). Others suit consumer goods (textile workers, farmland, food processing).
When a country starts switching towards capital goods, it moves its best-suited resources first, so the early gains are cheap. As it keeps switching, it runs out of well-suited resources and has to move badly suited ones: textile workers retrained as steelworkers, farmland concreted over for factories. Each extra unit now costs more of the other good.
Not every PPC bends. If resources can move between the two goods with no loss of efficiency, the opportunity cost stays the same and the PPC is a straight line. For example, if a country can make 120 phones or 40 laptops and its workers can switch freely between them, 1 laptop always costs \( 120 \div 40 = 3 \) phones. Straight-line PPCs are rare in reality, but they are handy for the trade examples in Step 3.
| Shape | Opportunity cost | Resources |
|---|---|---|
| Straight line (linear) | Constant | Perfectly interchangeable |
| Bowed outward (concave) | Rising | Better suited to one good than the other |
Shifts: growth and shocks
The limits on what an economy can produce are not fixed forever. When the whole curve moves outward, the economy can produce more of both goods. This is what economists mean by economic growth. The chapter gives four drivers:
- More resources: a larger labour force, more capital, or new natural resources. When Saudi Arabia discovered oil in 1938, its PPC shifted dramatically outward.
- Better technology: new methods that get more from the same inputs, as in the Industrial Revolution.
- Better human capital: education and training. South Korea’s rise from one of the poorest countries in 1960 to one of the richest by 2020 was driven heavily by investment in schooling.
- Better institutions: stronger laws, clearer property rights, less corruption.
A shift can be even, or biased towards one good. A new farming technology might push the curve out mostly along the food axis.
The curve can also shift inward, meaning the economy has lost capacity. Causes include war, natural disasters, pandemics, resource depletion and loss of skilled workers. Germany in 2022 is a clear example: its industry relied on cheap Russian gas, and when supplies were cut after Russia invaded Ukraine, energy-intensive output fell sharply. Because energy feeds into almost everything, the whole curve contracted, with the biggest fall in energy-intensive goods.
| Event | On the diagram |
|---|---|
| Government switches production from cars to tanks | Movement along the curve |
| Recession, unemployment rises | Movement to a point inside the curve |
| Unemployment falls back | Movement from inside towards the curve |
| New technology or more workers | Outward shift of the curve |
| War or natural disaster destroys factories | Inward shift of the curve |
The PPC has limits: it shows only two goods at one moment, says nothing about who gets the output, and ignores pollution.
Practise: 6 questions
Try each one on paper first, then check the worked answer.
EasyQ1. A country’s PPC passes through (40, 40). It is producing 25 capital goods and 25 consumer goods. Where is it relative to the PPC, and what does this tell you? Show worked answer
Resources are being underused: there is unemployment, idle capacity or waste. The economy may be in a recession.
EasyQ2. A country can make at most 120 phones or 40 laptops, and its PPC is a straight line. What is the opportunity cost of 1 laptop? Show worked answer
Because the PPC is linear, this cost is the same everywhere on the curve. (The reciprocal: 1 phone costs 40 ÷ 120 = 1/3 of a laptop.)
MediumQ3. An island’s PPC passes through W (0 coconuts, 100 fish), X (30, 90), Y (50, 60) and Z (60, 0). Find the opportunity cost per coconut for W to X, X to Y and Y to Z. Is the PPC concave? Show worked answer
X to Y: gain 20 coconuts, lose 30 fish. OC = 30 ÷ 20 = 1.5 fish per coconut.
Y to Z: gain 10 coconuts, lose 60 fish. OC = 60 ÷ 10 = 6 fish per coconut.
Yes, it is concave: the opportunity cost rises from 0.33 to 1.5 to 6 as more coconuts are produced. This is the Law of Increasing Opportunity Cost.
MediumQ4. State whether each event is a movement along the PPC, a movement inside it, or a shift (and which direction): (a) a major oil field is discovered; (b) a deep recession pushes unemployment to 12%; (c) a drought destroys 20% of farmland. Show worked answer
(b) Movement to a point inside the curve: resources are idle, but capacity has not changed.
(c) Inward shift: fewer resources, hitting food production hardest.
MediumQ5. A country has 1,000 labour-hours a week. A tonne of wheat takes 2 hours and a metre of cloth takes 4 hours. Workers can switch freely. (a) Maximum wheat? (b) Maximum cloth? (c) OC of 1 metre of cloth? (d) Is the PPC linear or concave? Show worked answer
(b) 1,000 ÷ 4 = 250 metres of cloth.
(c) 1 metre of cloth uses 4 hours, which could make 4 ÷ 2 = 2 tonnes of wheat. OC = 2 tonnes of wheat. (Check: 500 ÷ 250 = 2.)
(d) Linear: resources are perfectly interchangeable, so the OC is always 2 tonnes of wheat per metre of cloth. The line runs from 500 wheat to 250 cloth.
ExamQ6. Distinguish between a movement along a PPC and a shift of the PPC. Give one cause of each. [4 marks] Show worked answer
Cause: the government decides to produce more military goods and fewer consumer goods. (1)
A shift of the PPC means the whole curve moves because the economy’s productive capacity has changed, so it can make more (or less) of both goods. (1)
Cause: new technology or more resources (outward), or war or a natural disaster (inward). (1)
Check yourself
1. A point inside the PPC shows that:
2. The Law of Increasing Opportunity Cost explains why:
3. Which of these does NOT shift the PPC outward?
Your score: 0 out of 3
The short version
- The PPC shows the maximum combinations of two goods an economy can make with all its resources fully and efficiently used.
- On the curve is efficient, inside is inefficient, and outside is unattainable for now.
- Opportunity cost on the PPC is the slope, \( \Delta Y \div \Delta X \), measured in units of the other good.
- Most PPCs are concave because resources are not perfectly interchangeable; a straight-line PPC means constant opportunity cost.
- Growth shifts the curve outward (more resources, technology, human capital, institutions); war, disasters and pandemics shift it inward.
This guide covers the core of Chapter 2 of Economics Made Simple. The full chapter adds the Germany 2022 energy shock case study, labelled diagrams, the limitations of the model and a 15-question exam practice set with a full answer key.
Further reading on EconTutorials
Older in-depth articles on this topic from our blog: