The village of Nethergrove has one great asset: a wide stretch of common pasture, the green, where any villager may graze their animals. No one owns it. Everyone may use it. For generations it has fed the whole village.
You have just inherited a small herd, and the right to graze it on the green alongside three other herding families. How many animals you put out each season is entirely your choice. So is theirs.
You will graze the green for two spells of five seasons. Each season you decide how many animals to turn out. More animals means more milk and wool for you that season - but the grass only grows back so fast, and four herders are drawing on it at once.
Each season, choose how many animals to graze. The other three families choose too.
A health gauge shows the state of the pasture. Heavy grazing wears it down; light grazing lets it recover.
Five seasons on the green exactly as it has always been - unowned, unmanaged, open to all.
The same green, the same families - but this time under a new arrangement. See what difference it makes.
This is a place to explore, not a test. Graze boldly or graze gently - try whatever you like and watch what follows. By the end you'll have worked out for yourself how to:
The green is a common resource: no one owns it, and no one can be shut out. Anyone in Nethergrove may graze it. That openness is its virtue - and, as you may find, its weakness.
Each season every herder decides their own herd size. The green can feed only so many animals before the grass is worn down faster than it regrows. What happens to it depends on the choices of all four herders together - not any one of them alone.
Use the plus and minus to choose how many animals to turn out this season.
The other three families turn out their animals too. The green is grazed by every herd at once.
You earn from your herd this season, and the gauge shows how the green has fared.
Two things make up your final purse. Each season your animals bring in milk and wool. And at the very end, your surviving herd is worth a final sale - but only if the green is healthy enough to have kept your animals in good condition. A ruined pasture leaves a ruined herd.
After a spell like that, the families of Nethergrove gather. Everyone can see the green cannot go on this way. They agree to try something new for the next five seasons: a grazing quota.
From now on, every herder - you and the other three alike - may turn out 4 animals at most. No more. The hayward keeps the tally and the limit is binding on all. The green starts fresh. The same four families graze it again.
The green is a common resource: open to all, owned by none. Two features define it. It is non-excludable - no herder can be kept off. And it is rival - grass one animal eats is grass another cannot.
That combination is the trap. Each season, adding one more animal brought you the full gain in milk and wool. But the cost - a little more wear on the grass - fell on all four herders, and on every season still to come. The gain was private; the cost was shared.
So every herder, following their own sensible interest, had reason to keep adding animals. Each acting reasonably, together they wore the green to nothing. That is the tragedy of the commons - and it is a form of market failure, because an open market in grazing, with no rule and no owner, destroyed the very resource it depended on.
The quota did not change the green or the herders. It changed the choice. By capping every herd, it stopped the shared cost from ever growing faster than the grass could mend. No herder could gain by overusing the green, because no herder was allowed to.
| Approach | What it does | Seen in the wider world |
|---|---|---|
| Quotas and limits | Cap how much each user may take, so total use stays within what the resource can bear. | Fishing quotas, hunting permits, water abstraction licences. |
| Property rights | Give the resource an owner, who then has reason to protect its future value. | Enclosed farmland, private woodland, land ownership. |
| Regulation and charges | Tax or restrict the overuse, so users feel the shared cost themselves. | Carbon pricing, congestion charges, pollution permits. |
Each works in the same way: it makes the user face the cost that an open commons lets them ignore.
No one owns the open sea. Each fleet that lands more fish gains fully - while the shrinking stock is everyone's loss. Many fisheries have been fished to collapse.
The air is the largest commons of all. The gain from emitting is private; the cost of a changing climate is shared by all.
An open road is a commons. Each extra car gains the journey - and adds to the congestion that every other driver suffers.
One herder grazing gently could not save the green alone. That is the hard lesson - and exactly why shared rules exist.