Picture a lake full of fish and a village with ten boats. Nobody owns the lake. Each boat takes what it can. The fish breed, which is the lake's tap. Ten boats are ten drains on one tank.
Extra catch, to one owner20 tonnes, say
Lower lake, per boat2 tonnes, say
One more boat makes sense to its owner. The extra catch is all theirs. The lake running a little lower is shared by all eleven. A thing everybody uses and nobody owns is called a commons. The gain is private and the loss is shared, and that is the whole trouble with it.
The new boatkeeps the catch
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The lakeshared by all eleven
An eleventh boat joins. Who gets its catch, and who shares the lower lake?
Everybody shares both.
Not yet. The catch lands in one boat and is sold by one family. Only the loss is shared, which is why the loss keeps growing.
One owner gets the catch. All eleven share the loss.
Right. That split is the commons. Each owner's sums come out in favour of one more boat, and the lake's sums come out against all of them.
The one owner bears both.
Not yet. If the owner bore the whole loss, the sums would stop them. The lake is shared, so its loss is too, and the owner feels a tenth of it.
Picture the lake breeding 200 tonnes a year. Set how many boats fish it and how much each takes. The numbers are arithmetic on that rule.
Taken, a year50 tonnes
Bred, a year200 tonnes
Boats: 5 · Tonnes each, a year: 10
5 boats taking 10 tonnes each is 50. The lake breeds 200. It holds, with 150 tonnes to spare.
Taken, a year100 tonnes
Bred, a year200 tonnes
Boats: 5 · Tonnes each, a year: 20
5 boats taking 20 tonnes each is 100. The lake breeds 200. It holds, with 100 tonnes to spare.
Taken, a year150 tonnes
Bred, a year200 tonnes
Boats: 5 · Tonnes each, a year: 30
5 boats taking 30 tonnes each is 150. The lake breeds 200. It holds, with 50 tonnes to spare.
Taken, a year100 tonnes
Bred, a year200 tonnes
Boats: 10 · Tonnes each, a year: 10
10 boats taking 10 tonnes each is 100. The lake breeds 200. It holds, with 100 tonnes to spare.
Taken, a year200 tonnes
Bred, a year200 tonnes
Boats: 10 · Tonnes each, a year: 20
10 boats taking 20 tonnes each is exactly 200. In equals out. The lake holds.
Taken, a year300 tonnes
Bred, a year200 tonnes
Boats: 10 · Tonnes each, a year: 30
10 boats taking 30 tonnes each is 300. The lake breeds 200. It loses 100 tonnes a year, every year.
Taken, a year150 tonnes
Bred, a year200 tonnes
Boats: 15 · Tonnes each, a year: 10
15 boats taking 10 tonnes each is 150. The lake breeds 200. It holds, with 50 tonnes to spare.
Taken, a year300 tonnes
Bred, a year200 tonnes
Boats: 15 · Tonnes each, a year: 20
15 boats taking 20 tonnes each is 300. The lake breeds 200. It loses 100 tonnes a year, every year.
Taken, a year450 tonnes
Bred, a year200 tonnes
Boats: 15 · Tonnes each, a year: 30
15 boats taking 30 tonnes each is 450. The lake breeds 200. It loses 250 tonnes a year, every year.
Taken, a year200 tonnes
Bred, a year200 tonnes
Boats: 20 · Tonnes each, a year: 10
20 boats taking 10 tonnes each is exactly 200. In equals out. The lake holds.
Taken, a year400 tonnes
Bred, a year200 tonnes
Boats: 20 · Tonnes each, a year: 20
20 boats taking 20 tonnes each is 400. The lake breeds 200. It loses 200 tonnes a year, every year.
Taken, a year600 tonnes
Bred, a year200 tonnes
Boats: 20 · Tonnes each, a year: 30
20 boats taking 30 tonnes each is 600. The lake breeds 200. It loses 400 tonnes a year, every year.
Which settings keep the lake steady?
Only five boats. More boats always empty it.
Not yet. Ten boats at 10 each is 100 tonnes, half the tap. The number of boats is only half the drain; what each takes is the other half.
Any of them. The fish breed back whatever is taken.
Not yet. The fish breed 200 a year whatever the boats do. Past that, every extra tonne comes out of the stock, not the tap.
Any where boats times catch is 200 or less.
Right. The lake does not count boats. It counts tonnes out against tonnes bred. Ten boats at 20 and five at 30 both hold; twenty at 10 is the line.
Move both controls.
One ownerthe lake is theirs
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The statea rule or a tax
In 1968 a biologist called Garrett Hardin wrote a famous paper about this. He called it the tragedy of the commons, and said the way out was to make the lake somebody's property, or to have a government ration who may fish it, by a rule or by a tax.
The users meet→They set the limit→They watch each other→A cheat pays
Elinor Ostrom went looking. She collected studies of real commons, mountain pastures in Switzerland, village forests in Japan, irrigation canals in Spain, and compared them. Many had lasted for centuries with neither an owner nor the state. The users wrote their own rules and watched each other. She won the Nobel prize for economics in 2009.
Each card is a rule a village might use for its lake. Does it fit the pattern Ostrom found in the commons that lasted, or break it?
One card at a time. Tap the pile it belongs to.
Card 1 of 6
Everyone can see what everyone else takes
A cheat pays a small penalty the first time, and a bigger one if they keep on
The limit is set by officials who have never seen the lake
There is no written limit; people are trusted to be sensible
The users meet and agree the limit between them
Anyone caught cheating once is banned for ever
Everyone can see what everyone else takes → Fits the pattern
Not yet. Fits. A rule nobody can check is a wish. In the commons that held, the users themselves did the counting, often in public.
A cheat pays a small penalty the first time, and a bigger one if they keep on → Fits the pattern
Not yet. Fits. A first slip gets a warning; a habit gets a real cost. Ostrom found this pattern again and again, and called it graduated sanctions.
The limit is set by officials who have never seen the lake → Breaks the pattern
Not yet. Breaks the pattern. In the commons that lasted, the users set the limit themselves. A limit set far away does not fit the lake and is not trusted.
There is no written limit; people are trusted to be sensible → Breaks the pattern
Not yet. Breaks the pattern. Sensible people with private gains and shared losses still add the eleventh boat. The lasting commons agreed a limit everyone could name.
The users meet and agree the limit between them → Fits the pattern
Not yet. Fits. A rule you helped make is a rule you understand and are likely to keep, and to see others keep.
Anyone caught cheating once is banned for ever → Breaks the pattern
Not yet. Breaks the pattern. The lasting commons punished in steps, small first. A punishment that harsh is rarely used, because nobody wants to end a neighbour over one slip.
3Fits
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3Breaks
Right. Three rules the lasting commons shared: the users set the limit, the users can see each other's take, and a penalty that starts small. The other three each break one of those.
Before 19953 days of fishing a year, Gulf of Alaska
After 1995240 days of fishing a year, Gulf of Alaska
A rule needs a count. Alaska's halibut fishery once ran as a race: by the late 1980s the Gulf of Alaska season was two or three days of flat-out fishing. From 1995 each boat got its own share of a yearly total set by the count. The race stopped; the season stretched to about eight months.
Taken260 tonnes
Bred200 tonnes
The count says the lake breeds 200 tonnes a year. This year the boats took 260. How many tonnes did the stock lose?
tonnes
Right. Sixty. Not a lot against a big lake, which is why nobody notices the first year. Lesson 1's gap, lesson 3's drains: the same arithmetic, and the same slow end if it repeats.
The air over a city
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A road at rush hour
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Fish in the open sea
The air over a city. A public road at rush hour. The fish in the open sea. Which of these is a commons?
All three. Everybody uses them, nobody owns them, and one more user's cost lands on all.
Right. The shape is the test, not the setting. A car on a full road slows every other car; a chimney's smoke lands on every lung. Each is the eleventh boat.
Only the fish. Air and roads cannot run out.
Not yet. A road at rush hour runs out of space. Air runs out of cleanness. The running-out is slower, not absent.
Only the road and the sea. Air is free, so it cannot be a commons.
Not yet. Free is what makes a commons. No price on the drain is the reason each user takes a bit more than the tank can give.
Lesson complete
A shared tank empties because each user keeps the gain and shares the loss. Rules the users watch hold it.