The lesson
Use the concept, then apply it to a real decision. Use this page as a fast, high-quality revision pass—not a wall of notes to memorise.
The social versus private distinction
When a producer or consumer imposes costs or benefits on third parties, private and social outcomes diverge.
- Social cost = private cost + external cost.
- Negative externalities can lead to overproduction or overconsumption relative to the social optimum.
- Positive externalities can lead to underproduction or underconsumption.
Merit goods and policy choices
Merit goods may be underconsumed because people underestimate benefits or because wider benefits are not reflected in market prices.
- Taxes can internalise external costs; subsidies can encourage activities with external benefits.
- Regulation and information campaigns may help when price tools are impractical.
- Evaluate information gaps, enforcement, equity, unintended consequences and government failure.
Worked exam thinking
Worked example: pollution tax
Prompt: Why can a per-unit pollution tax improve allocation?
How to turn knowledge into marks
Use this answer route
For a focused explanation or short evaluation question on this topic:
- 1State the concept or relationship.
- 2Use the diagram, data or example accurately.
- 3Apply the impact to stakeholders.
- 4Evaluate the conditions and trade-offs.
Quick questions
Check your understanding
What is an externality?
A cost or benefit experienced by a third party who is not directly involved in the transaction.
Why are merit goods underconsumed?
Consumers may have imperfect information or ignore private and external benefits.
Why can government intervention fail?
Governments can face poor information, administration costs, lobbying and unintended effects.