Classification of goods and services

A public good has two defining characteristics. It is non-rival: one person's consumption does not reduce the amount available to others — for example, the protection given by national defence to one citizen does not reduce the protection given to anyone else. It is also non-excludable: it is impossible (or impractical) to prevent people who do not pay from consuming it — once defence exists, every citizen is protected whether or not they have contributed.

These characteristics cause the free-rider problem. Because non-payers cannot be excluded, each individual has an incentive to avoid paying and simply enjoy the good provided by others — they "free-ride". If every individual reasons in this way, few or none will pay, since each can benefit without contributing.

As a result, a private firm attempting to sell the good would be unable to generate reliable revenue. With no way to charge consumers and no income to cover costs, no profit-seeking firm will produce the good. The market therefore provides none of it, even though society as a whole would value it — a clear case of market failure (a missing market).

This is why public goods are typically provided by the government and funded through taxation: compulsory taxes remove the free-rider problem because everyone contributes, ensuring that socially valuable goods such as defence, street lighting and flood defences are supplied.

A merit good is under-consumed in a free market because consumers undervalue its benefits through imperfect information (e.g. education); a demerit good is over-consumed because consumers underestimate its harm (e.g. cigarettes). Since the two problems are mirror images, it seems natural for governments to treat them in opposite ways.

The case for opposite treatment. For a merit good the aim is to raise consumption towards the socially desirable level, so the government subsidises it (lowering price), provides it directly (e.g. free state schooling), or informs consumers of its benefits. For a demerit good the aim is to reduce consumption, so the government taxes it (raising price), regulates or bans it (age limits), or informs consumers of its harm. Because the underlying failures point in opposite directions (too little vs too much), opposite policy directions are logically appropriate, and in each case correcting the information failure is a shared starting point.

Qualifications and limitations. The treatments are not perfectly symmetric. Demerit goods are often addictive, so price-based measures may have little effect on demand and information may be ignored — stronger regulation may be needed. Subsidies for merit goods are costly and have an opportunity cost, and over-provision can be wasteful. Both interventions risk government failure (poor information, unintended effects such as black markets from bans). There are also value judgements about which goods count as merit or demerit, so the 'opposite' treatment rests partly on normative grounds.

Judgement. Treating merit and demerit goods in broadly opposite ways is justified, because their market failures genuinely run in opposite directions and the policy tools naturally mirror each other (subsidise vs tax, encourage vs discourage). However, the treatment should not be mechanically symmetric: the best mix depends on factors such as addictiveness, price sensitivity, cost and the risk of government failure. The most defensible conclusion is that opposite directions of policy are appropriate, but the specific tools and intensity must be tailored to each good rather than simply reversed.

Each measure in the source addresses a different type of good.

Street lighting is a public good: it is non-rival (one person benefiting from the light does not reduce it for others) and non-excludable (you cannot stop passers-by from using it), so the market would not provide it and the council must.

The public park is best described as a quasi-public good: it is largely non-rival and non-excludable when uncrowded, but it can become rival if congested and entry could in principle be charged — so it has some, but not all, public-good features.

The warning campaign about sugary drinks addresses a demerit good: sugary drinks are over-consumed because consumers underestimate the harm (imperfect information), so the council provides information to reduce consumption.

Subsidising adult education addresses a merit good: education is under-consumed because its benefits are undervalued (imperfect information), so the subsidy lowers the price to raise consumption towards the socially desirable level.

A public good is non-rival and non-excludable, so the free-rider problem prevents the free market from providing it. This is the central argument for government provision.

The case for government provision. Because non-payers cannot be excluded, a private firm cannot earn reliable revenue, so it will not supply the good even though society values it. The government can solve this by providing the good directly and funding it through taxation, which removes free-riding because everyone is compelled to contribute. For genuinely pure public goods such as national defence, this argument is very strong — there is essentially no market alternative, so without government provision the good would not exist at all.

The case against / qualifications. First, government provision does not mean government must produce the good itself — it can fund provision while contracting private firms to build and run it (e.g. paying a company to construct flood defences). So 'provided by the government' is too strong if it implies state production. Second, many goods called 'public' are really quasi-public goods (roads, parks) where some excludability is possible (tolls, entry fees), so private or mixed provision can work. Third, government provision can suffer government failure — inefficiency, poor information about how much to provide, and the opportunity cost of the tax revenue used. Deciding the optimal quantity of a public good is itself difficult because there is no market price to reveal demand.

Judgement. Government involvement is justified for public goods because the free-rider problem otherwise leaves them unprovided, and for pure public goods such as defence, direct government provision is clearly appropriate. However, the claim that the government should provide all public goods is too strong: the government's essential role is to ensure provision and fund it, but it can often achieve this by financing private production rather than producing the good itself, and many 'public' goods are quasi-public and partly marketable. The most defensible conclusion is that the government must guarantee and finance public goods to overcome market failure, but need not always be the direct provider.