This is the final exam for Tragedy of the Commons. It pulls together everything: the engine (private benefit, socialized cost), what makes a resource a common-pool resource (rivalrous and non-excludable), why each actor is behaving rationally — the externality and the prisoner’s-dilemma structure at its heart — the limits of the model (when a shared resource is not a tragedy), the real cases (overfishing, antibiotic resistance, traffic, groundwater, the atmosphere, spam), and the ways out (property rights, regulation and quotas, Pigouvian taxes, and Elinor Ostrom’s self-governance) along with where each one fails. Take your time and reason each one through; several look easy until you spot the trap — blaming character instead of structure, crying “tragedy!” at a non-rival resource, or reaching for one universal cure.
How this exam works
Read carefully — this exam is final. Each question appears one at a time. Once you submit an answer it is locked for good: there’s no going back, no retry, and no restart. Your score is hidden until the end, where you’ll see a pass/fail verdict. The pass mark is 70%. A few questions ask you to select all correct answers.
What is the cleanest statement of the engine behind the tragedy of the commons?
Select an answer to continue.
Course Recap
Big picture
Tragedy of the commons, in one picture
- Tragedy of the Commons
- The engine
- A shared, rivalrous, non-excludable resource (a common-pool resource): the benefit of taking is private, the cost is socialized — so rational individual choices sum to collective ruin
- A trap, not a vice
- Each actor is rational; the ruin is structural. It runs on a negative externality (a cost you don’t pay) and is an N-player prisoner’s dilemma — same people conserve under a different structure
- When it does NOT bite
- Non-rival / superabundant, excludable / owned, or a small group that monitors and builds reputation (a repeated game). Don’t cry "tragedy!" at every shared thing
- The commons around us
- Overfishing (Grand Banks cod), antibiotic resistance, traffic, groundwater, the atmosphere, spam — and why an unadjusted market price leaves the externality out
- Escaping the tragedy
- Change who bears the cost: property rights / catch-shares, regulation & quotas, Pigouvian taxes & congestion pricing, and Ostrom’s self-governance — no panacea; match (or blend) the fix to the resource
- The engine
Key takeaways
The tragedy of the commons is a disaster that needs no villain: when a shared resource is free to take but its cost is split among everyone, each user is rewarded for overusing it, so individually rational choices add up to collective ruin. It bites on a common-pool resource — rivalrous and non-excludable — and it’s a trap, not a vice: the ruin is structural, running on a negative externality (a cost the taker doesn’t pay) and shaped like an N-player prisoner’s dilemma. It does not bite when the resource is non-rival, excludable or owned, or governed by a small, watchful group. You’ll find the identical machine in overfishing, antibiotic resistance, traffic, groundwater, the atmosphere, and spam — and an ordinary market price won’t save it, because the price leaves the socialized cost out. The fixes all work by changing who bears the cost of taking: property rights, regulation and quotas, Pigouvian taxes that price the externality in, and Elinor Ostrom’s community self-governance with monitoring and graduated sanctions. There is no single cure — read the specific commons and match, or blend, the remedy to its structure.