---
title: "Market Failure: Externalities and Public Goods"
description: "External costs and benefits can be omitted from private decisions, leading competitive markets to produce too much or too little. Public goods are nonrival and nonexcludable, so voluntary funding can "
canonical: https://lightmysky.com/learn/civics-and-economics/market-failure-externalities-and-public-goods-mt_TvBDQJqv1R
source: https://lightmysky.com/learn/civics-and-economics/market-failure-externalities-and-public-goods-mt_TvBDQJqv1R.md
retrieved: 2026-11-12
---

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# Market Failure: Externalities and Public Goods

External costs and benefits can be omitted from private decisions, leading competitive markets to produce too much or too little. Public goods are nonrival and nonexcludable, so voluntary funding can fall short. Taxes, donations and other arrangements can help fund them.

Subject: Civics & Economics · Area: Economics · Ages 15 to 16
Page: https://lightmysky.com/learn/civics-and-economics/market-failure-externalities-and-public-goods-mt_TvBDQJqv1R

## Ready when they can

- Compare private cost with social cost for a polluting factory and show why the market quantity is too high
- Choose a tool for a stated failure (a tax, a subsidy, a tradable permit, a rule) and justify the choice
- Explain free riding and why street lighting is not sold lamp by lamp

## Lesson: When prices miss shared costs and benefits

An unregulated competitive factory pays its production costs but leaves pollution damage unpaid. Social cost adds outside harm to private cost. Ignoring it leads to output above the socially efficient level. Unlike a single-price monopoly restricting output, this failure can mean excess output. A pollution charge brings harm into decisions; uncovered polluters still ignore it. Enforced permits cap emissions. Firms with cheaper cleanup sell unused permits to firms with costlier cleanup, directing cuts toward lower costs. For equally harmful units, limiting emissions also limits harm. Rules can restrict damaging activities.

**Example.** Street lighting is nonrival: one person using its light leaves it available to others. It is nonexcludable: excluding passing nonpayers is impractical. These features make it a public good. Sellers cannot readily charge every beneficiary, so voluntary payments may fund too little. Taxes can fund lighting collectively. Donations or other arrangements can also work; public goods do not always require tax funding.

A free rider enjoys a shared benefit without contributing to its cost. A family skips a patrol collection because the patrol passes its street anyway. If too many people do this, funds may fall short. For example, a patrol needs £90 but receives £60, leaving £30 unfunded. Cooperation, donations or compulsory payments can address the gap.

A beekeeper may benefit an orchard through unpaid pollination. This positive externality is a benefit outside the beekeeper's own return. If this benefit is ignored and no agreement pays for it, beekeeping may be below the socially efficient level. A subsidy tied to that benefit can encourage provision. Private agreements can help too. Support must be assessed against its costs; a spillover does not justify any subsidy amount.

**Recap.** Count outside costs and benefits. Match a policy to the incentive or funding gap it needs to address.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Competition, Market Power and Barriers to Entry](https://lightmysky.com/learn/civics-and-economics/competition-market-power-and-barriers-to-entry-mt_7rSbpD7hJ1)

## Optional connections

- [Externalities and Spillovers](https://lightmysky.com/learn/civics-and-economics/externalities-and-spillovers-mt_F4SQsGpZk9)

## Opens up

- [What Extraction Costs the Place It Happens](https://lightmysky.com/learn/geography/what-extraction-costs-the-place-it-happens-mt_diS2vBXcV4)