Public Goods
Public goods are goods and services characterised by non-excludability (cannot prevent non-payers from consuming) and non-rivalry (one person's consumption does not reduce availability for others). Pure public goods include defence, lighthouses, and street lighting. These characteristics cause market failure because profit-seeking firms cannot charge users.
Real World
The UK's nuclear deterrent, Trident, protects every resident equally — one person being defended does not reduce protection for others, and no taxpayer can be excluded from its security umbrella.
Exam Focus
Define both non-rivalry and non-excludability separately before explaining why markets fail — this secures full definition marks.
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