The Lake
Garrett Hardin argued that anything open to everyone gets used up. Elinor Ostrom went and looked, and found communities that had shared pastures, fisheries and canals for generations. Eight villages fish this lake. You can't fish. You can only change the rules below.
Pink boats are outsiders. Lanterns glow with each village's trust. A red ring means a village was caught over the limit.
Fish in the lake, last 200 seasons
Fish Capacity Half capacity, where regrowth peaksHow the model works
- A healthy lake holds 1,000 fish. Regrowth peaks at half capacity, at 100 fish a season, with good and bad years drawn at random. Below 150 fish, spawning starts to fail.
- With no catch limit, villages add effort while fishing still pays. That drives the lake down to where it just breaks even: 200 fish. Starting from 800, the rush of new boats overshoots and the lake empties. Then fish drift back in from upstream and it runs thin at about 200, for half the catch it could sustain. A restocked lake, at 500 fish, runs thin without emptying.
- With a limit, each village decides every season whether to take extra. Greed pushes one way; trust, the odds of being caught, and the size of the next penalty push back.
- Trust drifts toward a level set by who made the rules: higher when the villages wrote them together. Seeing neighbours caught lowers it, and so does noticing the lake thin while you played fair, or getting a short share. Mediation softens these and speeds repair.
- A fixed limit is 90 fish a season. An adaptive one follows the counted stock and leans toward half capacity. Without monitoring, the count is a guess.
- Without graduated sanctions, every offence gets one ruinous fine, which neighbours impose only 30% of the time and which leaves a grudge when they do. If they always imposed it, a flat fine would work as well. That 30% is my assumption.
- Ostrom called her principles best practices, not a recipe. In a 2016 study of 69 commons, no single principle was enough on its own.
- Every number here is a choice I made, not a measurement. The whole model is about 200 lines of JavaScript inside this page. Read it, change it, argue with it.
Real commons
Thirty years after his essay, Hardin wrote that he should have said unmanaged commons.
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Alanya, Turkey inshore fishery, since the 1970s
After years of fights over the best spots, about 100 fishers named every site, drew lots each September, and rotated daily, following the fish east and then west. The fisher whose turn it was saw any cheater. Disputes were settled at the coffeehouse.
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Törbel, Switzerland alpine meadows, records from 1224
A 1517 rule, still enforced in the 1970s: no one may summer more cows on the shared alp than they can feed through winter. Cows are counted on arrival because cheese is shared per cow, so monitoring costs almost nothing. An official fines violators and keeps half the fine.
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Valencia, Spain irrigation, since at least 1435
Each canal's farmers elect a syndic who farms land on it. The Water Tribunal meets on Thursday mornings outside the cathedral, without lawyers, and rules on the spot. In nearby Castellón's 15th-century fine books, two-thirds of those fined in a year were one-time offenders.
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Maine, USA lobster, zone councils since 1995
You need a state licence and acceptance by your harbour's "gang", and then you fish only its territory. Since 1995, elected zone councils have set their own trap limits, which the state legislature had failed to pass.
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Grand Banks, Canada northern cod, collapsed 1992
Not an unmanaged commons: Ottawa set the quotas. Overfishing, not the environment, collapsed the stock. The 1992 moratorium cost about 30,000 jobs, and commercial fishing only reopened in 2024. Rules made far from the water can fail too.