Why will a free market fail to provide goods like street lighting and national defence at all?
Explain public goods using non-excludability and non-rivalry, and why the market fails to provide them
A clear O-Level answer on public goods. The two features of non-excludability and non-rivalry, the free-rider problem, why the market provides none of them, and why the government must provide them from taxation.
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What this dot point is asking
The syllabus wants you to explain what a public good is, using the features of non-excludability and non-rivalry, and to explain why a free market fails to provide public goods at all. The big idea is that some goods have features that make it impossible for a firm to charge for them, so no profit-seeking firm will produce them, even though society wants them.
The answer
What a public good is
Note that public good does not just mean a good provided by the government. It is a specific type of good defined by these two features.
Non-excludability
A good is non-excludable if, once it is provided, you cannot stop people from enjoying it, even if they have not paid. A street light shines on everyone who walks past, whether or not they helped pay for it. There is no way to switch it off for non-payers.
Non-rivalry
A good is non-rival if one person's use does not reduce the amount left for others. When one more person benefits from the protection of the armed forces, there is no less protection for everyone else. The good is not used up by being consumed.
The free-rider problem
Because a public good is non-excludable, people can enjoy it without paying. Each person therefore has an incentive to let others pay and then use the good for free. This is the free-rider problem.
Why the market fails completely
If everyone tries to free-ride, a firm cannot get people to pay for the good. With no way to charge and no revenue, no profit-seeking firm will provide it. So the market provides none of the good, even though society values it. This is why public goods are a clear case of complete market failure, and why the government must provide them, funding them from taxation that everyone has to pay.
Examples in context
Example 1. Street lighting and defence in Singapore. Street lights and national defence protect and benefit everyone in Singapore at once, and no one can be excluded from them. Because firms cannot charge users, the government provides these public goods and pays for them from taxes, which is exactly what the theory predicts.
Example 2. Flood and coastal protection. Sea walls and drainage systems that protect a coastline are non-excludable and non-rival: they shield everyone in the area, and one person's protection does not reduce another's. A private firm could not charge each resident, so the government funds such defences, especially important for a low-lying, densely populated city.
Try this
Cue. State the two characteristics of a public good. It is non-excludable (no one can be stopped from using it) and non-rival (one person's use does not reduce the amount available to others).
Cue. Define the free-rider problem. Because a public good is non-excludable, people can benefit without paying, so each waits for others to pay; if everyone does so, too little or none of the good is funded.
Cue. Explain why the market provides none of a pure public good. Firms cannot stop non-payers from enjoying a non-excludable good, so they cannot charge for it and earn no revenue, meaning no profit-seeking firm will supply it.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original6 marksExplain the two main characteristics of a public good, using national defence as an example.Show worked answer →
A 6 mark question rewards both characteristics defined and applied to defence.
- Non-excludability
- A public good is non-excludable: once it is provided, no one can be prevented from enjoying it, even if they have not paid. National defence protects everyone in the country, including those who pay no tax.
- Non-rivalry
- A public good is non-rival: one person's use does not reduce the amount available to others. One more person being protected by the armed forces does not leave less protection for everyone else.
- Conclusion
- Because defence is both non-excludable and non-rival, it is a public good that the market cannot provide profitably, so the government provides it.
Markers reward both characteristics clearly defined and correctly applied to defence, with the conclusion that these features make it a public good.
Original5 marksExplain the free-rider problem and why it means a free market will not provide public goods.Show worked answer →
A 5 mark question rewards the free-rider idea and the link to market failure.
- The free-rider problem
- Because a public good is non-excludable, people can enjoy it without paying. Each person has an incentive to let others pay and then use the good for free, becoming a free rider.
- Why the market fails
- If everyone tries to free-ride, few or none will pay. A firm cannot charge for the good and so cannot make a profit, so no private firm will provide it. The market therefore provides none of the good, even though it is valued by society.
- Conclusion
- This is why the government must provide public goods, funding them through taxation that everyone has to pay.
Markers reward the free-rider idea linked to non-excludability, the point that firms cannot charge and so will not supply, and the conclusion that the government must provide and fund the good.
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