Market Failure & Externalities (Years 10–11) — Economics

When markets fail; external costs and benefits; merit and demerit goods; and how governments respond.

Market failure occurs when the free market, left alone, fails to allocate resources in the best interests of society — producing too much of some goods and too little of others. A common cause is externalities.

Why this matters Clean air, education and honest food labelling all affect people who never took part in a sale. When markets ignore these wider effects, real harm or waste follows — and this is where government has a role.

Private and external effects

An externality is a cost or benefit that falls on a third party who is not the buyer or the seller. External costs are negative spillovers, such as a factory's pollution harming a nearby community. External benefits are positive spillovers, such as a vaccinated person protecting others from illness.

Type	Example
External cost	Air pollution from a factory
External benefit	A trained worker helping the whole economy

The gap between the private cost a firm pays and the full social cost is the external cost falling on third parties, such as neighbours breathing polluted air.

Merit and demerit goods

Merit goods (e.g. education, healthcare) bring external benefits and tend to be under-consumed if left to the market.
Demerit goods (e.g. tobacco) carry external costs and tend to be over-consumed.

Common exam mistake: mixing up the policy tool - remember tax discourages demerit goods (external costs) and subsidy encourages merit goods (external benefits). Writing the two the wrong way round under exam pressure is a common slip.

How governments respond

Governments intervene to correct market failure. Common tools include:

Indirect taxes on goods with external costs, to raise their price and cut consumption.
Subsidies for goods with external benefits, to lower their price and raise consumption.
Regulation and bans, such as pollution limits or safety rules.
Provision and information, such as state schools or public health campaigns.

Each policy has drawbacks — taxes may be hard to set correctly and regulation can be costly to enforce — so governments weigh the benefits against the costs before acting. A tax set too high may cut useful production, while one set too low leaves the external cost uncorrected.

Exam technique: always name the specific third party affected by an externality ("neighbours breathing in the pollution", not just "other people") - precise, specific answers score more highly than vague ones.

Put these steps in order to show how a government corrects a negative externality with a tax:

Government identifies a good with external costs
It imposes an indirect tax on the good
The tax raises the price and shifts supply left
Quantity consumed falls towards the socially efficient level
The external cost to third parties is reduced

A helpful way to remember the whole topic is to ask two questions about any good. First, does it create a spillover onto third parties, and is that spillover a cost or a benefit? Second, is the good therefore over-consumed or under-consumed by the free market? The answers point straight to the right policy: discourage demerit goods with taxes or rules, and encourage merit goods with subsidies or provision. This links the idea of market failure back to the earlier chapters on demand, supply and the price mechanism.