Series Info...Trials, Triumphs & Trivialities #204:

Strategic Insights: The Tragedy of the Commons

by Shannon Appelcline

Two weeks ago I kicked off a new look at strategic game design with a discussion of The Prisoner's Dilemma. However, that's just one of a few theories for how people balance personal versus community gain. In this article and the next I'll be looking at two other models, starting with The Tragedy of the Commons.

Defining The Tragedy of the Commons

The Tragedy of the Commons is probably the oldest of the three theories that I'll be talking about. The idea goes back to antiquity. The term itself was originated by William Forster Lloyd when talking about Medieval villages in 1833. However, the theory didn't come into common use until Garrett Hardin wrote about it in Science magazine in 1968.

Therein he describes the tragedy thus:

Picture a pasture open to all. ... As a rational being, each herdsman seeks to maximize his gain. Explicitly or implicitly, more or less consciously, he asks, "What is the utility to me of adding one more animal to my herd?" This utility has one negative and one positive component.

1) The positive component is a function of the increment of one animal. Since the herdsman receives all the proceeds from the sale of the additional animal, the positive utility is nearly +1.

2) The negative component is a function of the additional overgrazing created by one more animal. Since, however, the effects of overgrazing are shared by all the herdsmen, the negative utility for any particular decision-making herdsman is only a fraction of -1.

In other words, given a situation where there is a limited, common resource, any greedy resource user can see a notable gain from overusing the resource, the downside of which is spread out among all users. The nominal tragedy occurs when all resource users begin engaging in this greedy behavior, thus utterly destroying the resource and ensuring that no one sees real gains.

Based on this definition, I include the following requirements in any Tragedy of the Commons:

  • A shared resource.
  • Degradation of that resource through overuse.
  • Personal gain through overuse of the resource.

Applying the Tragedy to Board Games

Strategy games--and particularly board games--are typically about abstraction. You take a big, complex real-life system, then you prune it down to its most salient one or three points, and base your game around that. This points out the main problem with using the Tragedy of the Commons in a strategy environment. The degradation element of the Tragedy lies below the level of abstraction in most games. Thus, you have to expand a strategy game's core modeling before you can apply the Tragedy.

However, expanding in this direction offers some pretty fertile new ground for strategic game design. Even without introducing a resource as Commons, you can have resources that fail to renew if they're overused, and thus you can give players the hard choice of whether to overuse their resources for a short-term gain, or to keep using them at equilibrium levels for the optimal long-term gains. Just imagine a wargame where you're being pressed hard by a foe, and you have to decide whether to excessively use a degradable resource to defeat them.

After that making the resource shared is just a variant.

An advantage of the Tragedy of the Commons is that--as stated--it's explicitly a multiplayer problem. Thus it offers good potential of applicability for games with many players.

Existing Tragedy Mechanics

As I've already said, the idea of a degradable resource is pretty rare in games. Likewise, the complete Tragedy, where individual overuse incurs group loss hasn't been explicitly plotted out in any major game that I'm aware of.

However, the start of the Tragedy is a shared resource, and we can occasionally find that in games. Clippers is a game where all players can move join ship lines. Age of Gods is a wargame that lets players move any of the armies. Clans lets you move any of the human civilizations on the board. However, these are all very much give-and-take games. You take advantage of the joint resources to do something good for yourself and/or bad for the other players. There's no greater resource production that you're damaging.

And though I couldn't come up with any specific examples of the Tragedy in existing games, I did come across two games which skirt the idea.

Reiner Knizia's Buy Low, Sell High is a pretty standard stock market model. An individual player can sell off some of his stock, profit-taking, and in doing so he damages the value of the stock for everyone.

Martin Wallace's Brass envisions the creation of an overall economy. By building out already saturated industry categories, a player can damage the value of all extant industries in that category--though turning this to his advantage is somewhat trickier.

A Tragedy Mechanic

For my sample Tragedy mechanic, I've adopted Hardin's original example, with a nod toward The Settlers of Catan.

The Pasture. Imagine a Settlers-like game where multiple players can all house flocks of sheep in a pasture. Whenever the space produces, each player gets one sheep card per flock. However, there's also a limit to the number of flocks that can be safely housed. For each flocks in excess of that number, the group as a whole must pay back one sheep card. These excess sheep are paid back equally among all the players, with a simple heuristic or a random roll determining who pays sheep that can't be equally divided.

To further play up the idea of degradation we can introduce one or two variants to make things tougher. Either (1) each turn in which the pasture is overused, its limit goes down by one or more -or- (2) the payoff number never goes down, so even if the field is later underutilized, players continue having to pay off for past damage.

Any of these methods should allow a very simple, but real, model of the Tragedy of the Commons in a game.

Applying the Tragedy to Reality TV Shows

One of the interesting elements of TV reality shows like Survivor is that they already contain a lot of these societal and economic models: the Tragedy of the Commons is one such. For example, if you hear contestants in Survivor complain that someone is eating too much, that's the Tragedy of the Commons.

Perhaps that's sufficient, though I think there are some possibilities for making the Tragedy an even more explicit part of the gameplay. If we presume that votes are the main currency of most of these games, then applying the Tragedy of the Commons to them explicitly requires turning the votes into a common resource.

In Survivor I can imagine a situation where each initial team has a set number of "extra" votes. They could be used up early on to get out team members that you don't like, or they could be saved to be used after the merge--but any player could choose to use them with no agreement from the others. It would make everything a lot more tense, even when there's clear consensus about who should go.


I suspect that the Tragedy of the Commons contains some of the most untapped potential for strategic game design of the three models that I'll be talking about.

In two weeks I'll move on to the third and last: the Free Rider Problem.

[ <— #203: Strategic Insights: The Prisoner's Dilemma | #205: Strategic Insights: The Free Rider Problem —> ]

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