You are viewing a free preview of this lesson.
Subscribe to unlock all 10 lessons in this course and every other course on LearningBro.
Public goods are the purest case of market failure — a case of complete market failure, where the free market provides the good not at all, even though it is socially valuable. The reason lies in the good's characteristics: because no one can be charged and no one's consumption uses the good up, private firms can neither earn revenue nor have any incentive to supply. The result is a missing market. Understanding public goods means analysing the two defining characteristics (non-rivalry and non-excludability), the free-rider problem they generate, the spectrum running from pure to quasi-public goods, the related tragedy of the commons, and why the state must therefore step in.
Key Definition: A public good is a good that is both non-rivalrous (one person's consumption does not reduce the amount available to others) and non-excludable (it is impossible, or prohibitively costly, to prevent non-payers from consuming it once it is provided).
Paul Samuelson (1954), in The Pure Theory of Public Expenditure, gave the foundational analysis, proving that the market mechanism cannot efficiently provide goods that are simultaneously non-rival and non-excludable.
Part of 4.1.8 — Market mechanism, market failure and government intervention, within microeconomics (4.1).
A good is non-rival when one person's consumption does not reduce the amount available to others — the marginal cost of supplying an extra consumer is effectively zero.
A good is non-excludable when it is impossible (or prohibitively expensive) to prevent non-payers from consuming it once provided.
The two characteristics are logically distinct, and a good can have one without the other (see quasi-public goods below). It is the combination that produces a pure public good — and it is non-excludability specifically that wrecks the market.
Plotting the two characteristics as axes generates a 2×2 taxonomy of all goods. Excludability runs along one axis, rivalry along the other; the four quadrants are private goods, public goods, common-pool resources, and club (or "toll") goods.
This matrix is worth memorising. Private goods (top-left) are both rival and excludable — the everyday goods the market handles well. Club goods (top-right) are non-rival but excludable, so the market can supply them by charging (satellite TV, a toll motorway, a members-only gym). Common-pool resources (bottom-left) are rival but non-excludable — the danger zone of the tragedy of the commons. Public goods (bottom-right) are both non-rival and non-excludable, so the free-rider problem produces a missing market. Quasi-public goods sit near the boundaries, sharing properties of more than one cell, and technology can slide a good from one quadrant to another (encryption moved broadcast TV from "public" toward "club").
Exam Tip: Drawing or describing this 2×2 matrix is an efficient way to define public goods in context and to show you understand that the public-good category is one corner of a wider taxonomy. It also primes the tragedy-of-the-commons and quasi-public-good analysis that earns evaluation marks.
The combination of non-rivalry and non-excludability creates the free-rider problem — the fundamental reason the free market does not provide public goods.
Key Definition: The free-rider problem occurs when individuals can enjoy a good without paying for it, because the good is non-excludable. This destroys the incentive to pay voluntarily, so private provision is unprofitable and the good is not supplied.
The logic:
This is a prisoner's-dilemma structure: individually rational behaviour produces a collectively irrational result. Everyone would be better off if everyone contributed, yet each person's dominant strategy is to free-ride. The mermaid flow below traces the logic from characteristics to the need for state provision.
flowchart TD
A[Non-excludable AND non-rival] --> B[Each person can benefit without paying]
B --> C[Dominant strategy: free-ride]
C --> D[No one pays voluntarily]
D --> E[No effective demand / missing market]
E --> F[Private firms will not supply]
F --> G[State provision funded by compulsory taxation]
Exam Tip: Pin the free-rider problem on non-excludability, not non-rivalry. Non-excludability is what lets people consume without paying; non-rivalry merely means the marginal cost of an extra consumer is zero. Many candidates blur the two and lose the AO3 mark for the precise mechanism.
| Good | Non-Rival? | Non-Excludable? | Notes |
|---|---|---|---|
| National defence | Yes — protecting one citizen does not reduce protection for others | Yes — no resident can be excluded from being defended | Funded from general taxation |
| Street lighting | Yes — one person's use does not dim it for others | Yes — anyone on the street benefits | Funded by councils via council tax |
| Flood defences | Yes — protecting one property does not reduce protection for neighbours | Yes — all properties behind the defence benefit | Managed by the Environment Agency in England |
| Lighthouse beams | Yes — one ship's use does not reduce the beam for others | Yes — all ships in range can see the light | Historically debated (Mill vs Coase) |
| Crime deterrence / rule of law | Yes — deterrence protects all simultaneously | Yes — cannot confine the rule of law to payers | Funded from taxation |
In reality, few goods are perfectly non-rival and non-excludable. Many display these properties to a degree but not completely. These are quasi-public goods.
Key Definition: A quasi-public good is a good that possesses some but not all of the characteristics of a pure public good — it may be partially rival, partially excludable, or both.
| Good | Non-Rival? | Non-Excludable? | Explanation |
|---|---|---|---|
| Roads | Partially — non-rival when uncongested, but rival when congested (one car raises others' journey times) | Partially — tolls and congestion charges can exclude, but most roads are open | The M6 Toll charges drivers; most A-roads are free |
| Parks and beaches | Partially — non-rival at low use, rival when crowded | Partially — some charge entry (Kew Gardens); many are open access | Brighton beach is free but congested in summer |
| NHS hospital care | Partially — one patient occupying a bed makes it unavailable to others (rival in the short run) | Broadly non-excludable — free at the point of use to UK residents | Funded through general taxation |
| Broadcast / streaming TV | Non-rival — one viewer does not affect others | Increasingly excludable via encryption, logins and subscriptions | Sky and Netflix exclude; the BBC's licence model is imperfectly enforced |
| Public Wi-Fi | Partially — limited bandwidth means extra users can slow it | Can be made excludable with passwords | Open café Wi-Fi is quasi-public |
Exam Tip: When asked whether something is a public good, apply the two tests systematically and ask whether technology has shifted the classification. "Television is now a quasi-public good because encryption has made it excludable even though it remains non-rival" is exactly the analytical move examiners reward over flat recall.
The road case repays closer study because it shows how rivalry can switch on with use. An uncongested road at 3 a.m. is genuinely non-rival — one extra car imposes no cost on anyone, so the marginal external cost of an additional user is zero. The same road at 8 a.m. is intensely rival: each additional car slows every other car, generating a negative congestion externality (Lesson 2). The good is therefore non-rival up to a capacity threshold and rival beyond it. This has two implications. First, the efficient price for road use is not constant — it should be roughly zero when the road is empty (charging would deter beneficial costless trips) and positive when it is congested (to ration scarce capacity and make drivers face the congestion externality). This is the economic logic of time-varying road pricing such as London's congestion charge and ULEZ, and of "smart" motorway tolling. Second, it explains why so many publicly provided services are quasi-public: a hospital, a school, a park or a motorway behaves like a public good while spare capacity exists, but like a rival private good once it is full, which is exactly when queues, waiting lists and congestion appear. Recognising that rivalry is often quantity-dependent rather than fixed is a hallmark of sophisticated analysis.
Closely related is the tragedy of the commons, identified by Garrett Hardin (1968). Whereas a public good is non-excludable and non-rival, a common-pool resource is non-excludable but rival — using it does deplete it.
Key Definition: The tragedy of the commons is the over-exploitation of a non-excludable but rival resource, because each user gains the full private benefit of use but bears only a fraction of the cost of depletion.
Examples include overfishing of shared seas, deforestation of open-access forests, over-grazing of common land, and groundwater depletion. Each user, acting rationally, takes as much as possible, and the resource is degraded for all — a negative-externality logic at scale. Remedies include assigning property rights (privatisation or tradable quotas), regulation (catch limits, bans), or — as Elinor Ostrom (1990) showed in Governing the Commons (Nobel Prize, 2009) — community self-governance through locally agreed rules, which can succeed without either full privatisation or central control. The contrast with pure public goods is instructive: because a common-pool resource is rival, the danger is over-use; because a public good is non-rival, the danger is under-provision.
Because of the free-rider problem, only the government can ensure pure public goods are supplied, and it funds them through compulsory taxation — since individuals cannot be excluded and would free-ride given the choice, payment must be collected through the tax system rather than voluntarily.
The hard part is the optimal level of provision. With no market price and no demand curve, the government must estimate how much citizens value the good, using:
Each method is imperfect, so the state may over- or under-provide relative to the true optimum — the seed of potential government failure (Lesson 10).
Samuelson's deeper insight was that the very arithmetic of demand differs for a public good. For a private good, the market demand curve is found by horizontal summation — at each price, we add up the quantities each consumer wants, because each unit is consumed by only one person. For a public good, the same unit is consumed simultaneously by everyone (non-rivalry), so society's demand is found by vertical summation — at each quantity, we add up the prices (marginal valuations) every citizen places on that unit. The socially optimal quantity is then where this summed marginal social benefit equals the marginal cost of provision.
Subscribe to continue reading
Get full access to this lesson and all 10 lessons in this course.