Externalities and Spillovers
Choices spill over onto people who had no say: a factory's smoke, a neighbour's loud music, a planted garden, a vaccination; why harmful spillovers get overproduced and helpful ones underproduced when nobody pays or is paid for them
What a learner can do afterwards
- Identify the third party affected by a choice (e.g., 'the whole street breathes the barbecue smoke')
- Sort spillovers into helpful and harmful (e.g., a flower garden on the street vs. litter left at the park)
- Suggest a way to handle a spillover (e.g., a rule, a fine or a reward, like a tax on pollution or a subsidy for bee-keeping)
1 · Read
Some choices only affect you. Others spill over onto people who had no say at all. Economists call this a spillover, or an externality. It happens any time your choice makes someone else's life better or worse, without them choosing it.
Think about a backyard barbecue. The person grilling chose to light the fire. But the whole street breathes the smoke, whether they wanted to or not. The neighbors never agreed to smell smoke tonight. That is a spillover.
Not every spillover is bad. A flower garden on your street lifts everyone's mood for free. That is a helpful spillover. Litter left at the park makes the park worse for every visitor. That is a harmful one. Sort each spillover by asking: does it help or hurt the people who never chose it?
When nobody pays for a harmful spillover, it keeps happening, because the person causing it never feels the cost. When nobody gets paid for a helpful spillover, it happens less than it could, because the person creating it never gets credit. A fine on pollution or a reward for bee-keeping can fix that by connecting the cost or benefit back to the person who caused it.
A spillover touches people who never chose it: harmful ones need a cost attached, helpful ones need a reward.
More to read
Key Terms
Here are some useful words for talking about spillovers.
External benefits (also called positive externalities): good things that spill over onto people who did not buy or choose the thing that caused them. Think of a neighbor who plants flowers. Everyone who walks by gets to enjoy them, even though they never paid for the seeds.
Free rider: someone who lets others pay for something shared and then enjoys it anyway. If everyone acts like a free rider, the shared thing might never get made at all.
Intellectual property: the laws, like patents and copyrights, that protect inventors and artists. They help people keep the benefit of their own ideas, so they have a reason to keep inventing.
The big idea: when a choice spills over onto people who had no say in it, we get too much of the harmful stuff and not enough of the helpful stuff, unless somebody steps in with a rule, a fine, or a reward.
Key Concepts and Summary
Why do people sometimes invent less than the world needs? It comes down to spillovers.
When someone invents something new, like a better solar panel, the good effects do not stop with the inventor. Other companies learn from the idea, copy parts of it, and build on it. Those benefits landing on other people are positive externalities, which means helpful spillovers.
The inventor paid for all the hard work, but only keeps part of the total benefit. The rest spills over to everyone else for free. So the reward for inventing feels smaller than the true value to the whole world. That is why helpful spillovers get underproduced: nobody is paid for the good they give away.
It works the other way for harmful spillovers, like factory smoke. The factory owner does not pay for the dirty air the neighbors breathe, so there is nothing stopping the factory from making too much of it.
Rules, fines, taxes, and rewards are ways to fix this. A tax on pollution makes the polluter feel the cost. A reward for good ideas helps inventors keep more of the benefit they create.
2 · Watch
En anglaisTake it off screen
Where it sits
Learn first
Optional connections
This opens up
Where this leads
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.