--- title: "Market Failure: Externalities and Public Goods" description: "Some costs and benefits land on people outside the deal, so a market makes too much of what pollutes and too little of what spills over as a benefit. Public goods sit further out still: nobody can be " 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: 2026-09-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Market Failure: Externalities and Public Goods Some costs and benefits land on people outside the deal, so a market makes too much of what pollutes and too little of what spills over as a benefit. Public goods sit further out still: nobody can be shut out and one person's use does not use them up, so no seller can charge for them and taxes fund them instead. 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 the market gets the quantity wrong A factory that fouls a river pays for labour and machines but not for the dead fish downstream. Its private cost sits below the true social cost, so it produces more than society wants. This gap is called a negative externality, and the market quantity ends up too high. The fix pushes private cost toward social cost: a tax prices the harm, a tradable permit caps it, a rule bans the worst of it. **Example.** Some goods refuse to be sold lamp by lamp. Street lighting is nonrival, since your use leaves just as much light for me, and nonexcludable, since nobody can fence the glow off from passers-by. Private sellers cannot charge everyone who benefits, so they supply too little or nothing. That is why councils fund street lights, lighthouses, and flood defences from taxes instead. A free rider enjoys the benefit while skipping the bill. One family refuses to chip in for shared security patrols, knowing the patrols pass their street anyway. If everyone reasons this way, the patrols never get funded even though all want them. Small groups can shame riders into paying, but big groups usually need taxes or rules. **Tip.** Benefits spill over too. A beekeeper's hives pollinate the orchard next door for free, and vaccines shield even the unvaccinated. Each case tempts free riding, so markets supply too little alone. Subsidies, public funding, or direct provision close the gap. Spot the spillover and you have found the policy target. **Recap.** Price the harm, fund what cannot be fenced, and expect riders wherever payment is voluntary. ## 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) - [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)