Tragic but common

OK, I know it’s a big government solution, which is not fashionable at present, but can we create a federal regulatory agency to license the use of the phrase “tragedy of the commons” so the writer or speaker will know what the hell the anecdote means? There are 140 kghits at present, which of course is an entirely bogus way of estimating the currency of the phrase, but gives an idea that it is used quite a bit. Wikipedia gets it, um, not entirely right, and in my opinion misses the point of the example the way that (in my experience) most people do. The originating article is online at Science in a very nice little package with a week’s worth of reading on the topic. Perhaps Science could appoint the certification board, who could give an on-line quiz, and then people who pass could put a little graphic with this writer understands it! or a similar phrase. Or, of course, the board could vet the articles themselves, although that would be wasteful. Presumably, once a writer has shown she gets it, she will continue to get it in any other articles. Of course, having said that, presumably now I must show that I get it, and my ignorance will be exposed, for maximum embarrassment all around. Still, here goes.

First of all, the example itself. This is a game for five players, each beginning with two cows and a pasture of size two. There is also a commons, which is a pasture of size ten. The purpose is, ultimately, to maximize money, which is obtained by trading in milk units, by mechanisms I won’t invent since this is only an example. A cow can be set to produce either milk units or calf units, but in order to produce either in a turn must be fed with a grass unit. A cow that gets no grass units for three turns dies, and no longer produces milk, breeds or eats. Now, pastures produce grass units every turn, since in this example grass germinates and grows overnight, but it follows the following principle: one new grass unit for each grass unit that was uneaten on the previous turn. That is, if you graze one of your cows on your private land, the one uneaten grass will double and there will once again be two grass units next turn. If, however, you graze both your cows, there will be zero remaining, and there will never again be any grass on that land never ever evermore. OK?

Now, first turn. What do you do, hotshot? Well, obviously, everybody should graze one cow on their own land, and one cow on the public pasture. At the end of the turn, the public pasture has five units remaining and goes back up to ten for the next turn, and everybody’s private land goes back up to two. Right? Terrific. Sure, irilyth could graze both cows on the commons, which would mean the next day he’d have two private grass-units (as would we all), but after six cows yesterday there would be only eight grass-units on the public land today. And after six today, there would be only four tomorrow. And the next day, somebody isn’t going to got milk. But why would irilyth do that? Sure, he might drive other people into bankruptcy, but that isn’t going to get him money any faster (without some mechanism for doing that, but that’s not in the example). And, of course, ultimately if he takes that strategy, the commons will shrink to zero, and then he will be worse off.

So we are all in it together. Right? Until there are calves. At which point, perhaps all on the same turn, suddenly there’s an incentive to take more than two units off the common land. In fact, if Michael chooses to restrict himself to one grass unit off the commons, one of his cows ain’t got milk (unless he buys hay, which may be cost-effective, if the game weren’t just an example). And if irilyth really does put that sixth cow on the commons, then next turn there will only be eight units, and Chaos and Wayman will get their calves next turn, so waiting doesn’t make long-term sense for Michael either. In fact, if he waits and nobody else does, then he’s out long-term over where he would have been had he cashed in on all that green and then paved over the commons. Right?

In fact, every maximizing play Michael makes, whether in the short term or the long term, leads to long term famine, right? Unless there is a binding agreement among all the players never to graze more than one cow on the commons. And each person in that agreement will have an incentive to be first person to break it, because although breaking the agreement leads to loss, having somebody else break it leads to more loss. That’s the tragedy; the problem with the game is not the strategy, it’s the setup. And there are setups more or like that in real life, although it isn’t always easy to tell which they are. Nash pointed out that there are also setups that lead to equilibrium, where people have choices that aren’t self-defeating. And it turns out that there are more Nash set-ups than tragic commons, I think, but there’s a good deal of argument about that.

Anyway, by putting this in game units, my point was that the game has no solution. In real life, an externally imposed solution (you will all cooperate or I’ll turn this car around right now) can work, which of course is how actual commons actually worked. Plus, by reducing things to games, you can spot a lot of things that don’t actually exist in the example but are projected in by blatherers.

For instance, there is no public good in this game. The tragedy of the commons is not a story of the conflict between private gain and public good, and anybody who says so will not be allowed to use the little seal of approval. It is true that, gosh, people like the big green space in the middle of town, but the point of the example is that when it’s gone, it’s an economic loss to the individual who is attempting to maximize. Similarly, the players are not being motivated by short-term thinking; long-term thinking will also lead to overgrazing, simply to make use of a vanishing resource. It isn’t short-term thinking to eat bananas before they go bad. So if anybody tells you that the tragedy of the commons is how short-term thinking leads to long-term disaster, report that person to the board.

The other thing that the tragedy of the commons is not is a description of the entire ecosystem, or the entire free market capitalist system, or any entire system. Systems don’t have the edges that games do; in the real world the players could buy more pastureland, or sell a charitable photocalendar for hay money, or genetically engineer faster-growing, more filling “golden grass” or slenderer cows, or they could all decide that they would be better off without getting any new calves (other than to replace dying ones) and rather than maximizing profit they will instead devote themselves to transcendental meditation. There are situations which really are like the setup in the tragedy of the commons, and the trick is to recognize them and change their rules as quickly as possible.

Now, how wrong did I get all that?

chazak, chazak, v’nitchazek,
-Vardibidian.