The Tragedy of the Commons
Garrett Hardin (1968)
"The Tragedy of the Commons," Garrett Hardin, Science, 162(1968):1243-
1248.
At the end of a thoughtful article on the future of nuclear war, J.B. Wiesner
and H.F. York concluded that: "Both sides in the arms race are…confronted
by the dilemma of steadily increasing military power and steadily decreasing
national security. It is our considered professional judgment that this
dilemma has no technical solution. If the great powers continue to look for
solutions in the area of science and technology only, the result will be to
worsen the situation.'' [1]
I would like to focus your attention not on the subject of the article
(national security in a nuclear world) but on the kind of conclusion they
reached, namely that there is no technical solution to the problem. An
implicit and almost universal assumption of discussions published in
professional and semipopular scientific journals is that the problem under
discussion has a technical solution. A technical solution may be defined as
one that requires a change only in the techniques of the natural sciences,
demanding little or nothing in the way of change in human values or ideas of
morality.
In our day (though not in earlier times) technical solutions are always
welcome. Because of previous failures in prophecy, it takes courage to
assert that a desired technical solution is not possible. Wiesner and York
exhibited this courage; publishing in a science journal, they insisted that the
solution to the problem was not to be found in the natural sciences. They
cautiously qualified their statement with the phrase, "It is our considered
professional judgment...." Whether they were right or not is not the concern
of the present article. Rather, the concern here is with the important
concept of a class of human problems which can be called "no technical
solution problems," and more specifically, with the identification and
discussion of one of these.
It is easy to show that the class is not a null class. Recall the game of tick-
tack-toe. Consider the problem, "How can I win the game of tick-tack-toe?"
It is well known that I cannot, if I assume (in keeping with the conventions
of game theory) that my opponent understands the game perfectly. Put
another way, there is no "technical solution" to the problem. I can win only
by giving a radical meaning to the word "win." I can hit my opponent over
the head; or I can falsify the records. Every way in which I "win" involves, in
some sense, an abandonment of the game, as we intuitively understand it. (I
can also, of course, openly abandon the game -- refuse to play it. This is
what most adults do.)
The class of "no technical solution problems" has members. My thesis is that
the "population problem," as conventionally conceived, is a member of this
class. How it is conventionally conceived needs some comment. It is fair to
say that most people who anguish over the population problem are trying to
find a way to avoid the evils of overpopulation without relinquishing any of
the privileges they now enjoy. They think that farming the seas or
developing new strains of wheat will solve the problem -- technologically. I
try to show here that the solution they seek cannot be found. The
population problem cannot be solved in a technical way, any more than can
the problem of winning the game of tick-tack-toe.
What Shall We Maximize?
Population, as Malthus said, naturally tends to grow "geometrically," or, as
we would now say, exponentially. In a finite world this means that the per-
capita share of the world's goods must decrease. Is ours a finite world?
A fair defense can be put forward for the view that the world is infinite or
that we do not know that it is not. But, in terms of the practical problems
that we must face in the next few generations with the foreseeable
technology, it is clear that we will greatly increase human misery if we do
not, during the immediate future, assume that the world available to the
terrestrial human population is finite. "Space" is no escape. [2]
A finite world can support only a finite population; therefore, population
growth must eventually equal zero. (The case of perpetual wide fluctuations
above and below zero is a trivial variant that need not be discussed.) When
this condition is met, what will be the situation of mankind? Specifically,
can Bentham's goal of "the greatest good for the greatest number" be
realized?
No -- for two reasons, each sufficient by itself. The first is a theoretical one.
It is not mathematically possible to maximize for two (or more) variables at
the same time. This was clearly stated by von Neumann and Morgenstern,
[3] but the principle is implicit in the theory of partial differential
equations, dating back at least to D'Alembert (1717-1783).
The second reason springs directly from biological facts. To live, any
organism must have a source of energy (for example, food). This energy is
utilized for two purposes: mere maintenance and work. For man
maintenance of life requires about 1600 kilocalories a day ("maintenance
calories"). Anything that he does over and above merely staying alive will be
defined as work, and is supported by "work calories" which he takes in. Work
calories are used not only for what we call work in common speech; they
are also required for all forms of enjoyment, from swimming and automobile
racing to playing music and writing poetry. If our goal is to maximize
population it is obvious what we must do: We must make the work calories
per person approach as close to zero as possible. No gourmet meals, no
vacations, no sports, no music, no literature, no art…I think that everyone
will grant, without argument or proof, that maximizing population does not
maximize goods. Bentham's goal is impossible.
In reaching this conclusion I have made the usual assumption that it is the
acquisition of energy that is the problem. The appearance of atomic energy
has led some to question this assumption. However, given an infinite source
of energy, population growth still produces an inescapable problem. The
problem of the acquisition of energy is replaced by the problem of its
dissipation, as J. H. Fremlin has so wittily shown. [4] The arithmetic signs in
the analysis are, as it were, reversed; but Bentham's goal is unobtainable.
The optimum population is, then, less than the maximum. The difficulty of
defining the optimum is enormous; so far as I know, no one has seriously
tackled this problem. Reaching an acceptable and stable solution will surely
require more than one generation of hard analytical work -- and much
persuasion.
We want the maximum good per person; but what is good? To one person it
is wilderness, to another it is ski lodges for thousands. To one it is estuaries
to nourish ducks for hunters to shoot; to another it is factory land.
Comparing one good with another is, we usually say, impossible because
goods are incommensurable. Incommensurables cannot be compared.
Theoretically this may be true; but in real life incommensurables are
commensurable. Only a criterion of judgment and a system of weighting are
needed. In nature the criterion is survival. Is it better for a species to be
small and hideable, or large and powerful? Natural selection commensurates
the incommensurables. The compromise achieved depends on a natural
weighting of the values of the variables.
Man must imitate this process. There is no doubt that in fact he already
does, but unconsciously. It is when the hidden decisions are made explicit
that the arguments begin. The problem for the years ahead is to work out
an acceptable theory of weighting. Synergistic effects, nonlinear variation,
and difficulties in discounting the future make the intellectual problem
difficult, but not (in principle) insoluble.
Has any cultural group solved this practical problem at the present time,
even on an intuitive level? One simple fact proves that none has: there is no
prosperous population in the world today that has, and has had for some
time, a growth rate of zero. Any people that has intuitively identified its
optimum point will soon reach it, after which its growth rate becomes and
remains zero.
Of course, a positive growth rate might be taken as evidence that a
population is below its optimum. However, by any reasonable standards, the
most rapidly growing populations on earth today are (in general) the most
miserable. This association (which need not be invariable) casts doubt on
the optimistic assumption that the positive growth rate of a population is
evidence that it has yet to reach its optimum.
We can make little progress in working toward optimum population size
until we explicitly exorcise the spirit of Adam Smith in the field of practical
demography. In economic affairs, The Wealth of Nations (1776) popularized
the "invisible hand," the idea that an individual who "intends only his own
gain," is, as it were, "led by an invisible hand to promote…the public
interest." [5] Adam Smith did not assert that this was invariably true, and
perhaps neither did any of his followers. But he contributed to a dominant
tendency of thought that has ever since interfered with positive action
based on rational analysis, namely, the tendency to assume that decisions
reached individually will, in fact, be the best decisions for an entire society.
If this assumption is correct it justifies the continuance of our present policy
of laissez faire in reproduction. If it is correct we can assume that men will
control their individual fecundity so as to produce the optimum population.
If the assumption is not correct, we need to reexamine our individual
freedoms to see which ones are defensible.
Tragedy of Freedom in a Commons
The rebuttal to the invisible hand in population control is to be found in a
scenario first sketched in a little-known Pamphlet in 1833 by a
mathematical amateur named William Forster Lloyd (1794-1852). [6] We
may well call it "the tragedy of the commons," using the word "tragedy" as
the philosopher Whitehead used it [7]: "The essence of dramatic tragedy is
not unhappiness. It resides in the solemnity of the remorseless working of
things." He then goes on to say, "This inevitableness of destiny can only be
illustrated in terms of human life by incidents which in fact involve
unhappiness. For it is only by them that the futility of escape can be made
evident in the drama."
The tragedy of the commons develops in this way. Picture a pasture open to
all. It is to be expected that each herdsman will try to keep as many cattle
as possible on the commons. Such an arrangement may work reasonably
satisfactorily for centuries because tribal wars, poaching, and disease keep
the numbers of both man and beast well below the carrying capacity of the
land. Finally, however, comes the day of reckoning, that is, the day when
the long-desired goal of social stability becomes a reality. At this point, the
inherent logic of the commons remorselessly generates tragedy.
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璵aking herdsman is only a fraction of - 1.
Adding together the component partial utilities, the rational herdsman
concludes that the only sensible course for him to pursue is to add another
animal to his herd. And another.... But this is the conclusion reached by
each and every rational herdsman sharing a commons. Therein is the
tragedy. Each man is locked into a system that compels him to increase his
herd without limit -- in a world that is limited. Ruin is the destination
toward which all men rush, each pursuing his own best interest in a society
that believes in the freedom of the commons. Freedom in a commons brings
ruin to all.
Some would say that this is a platitude. Would that it were! In a sense, it
was learned thousands of years ago, but natural selection favors the forces
of psychological denial. [8] The individual benefits as an individual from his
ability to deny the truth even though society as a whole, of which he is a
part, suffers. Education can counteract the natural tendency to do the
wrong thing, but the inexorable succession of generations requires that the
basis for this knowledge be constantly refreshed.
A simple incident that occurred a few years ago in Leominster,
Massachusetts shows how perishable the knowledge is. During the Christmas
shopping season the parking meters downtown were covered with plastic
bags that bore tags reading: "Do not open until after Christmas. Free parking
courtesy of the mayor and city council." In other words, facing the prospect
of an increased demand for already scarce space, the city fathers
reinstituted the system of the commons. (Cynically, we suspect that they
gained more votes than they lost by this retrogressive act.)
In an approximate way, the logic of the commons has been understood for a
long time, perhaps since the discovery of agriculture or the invention of
private property in real estate. But it is understood mostly only in special
cases which are not sufficiently generalized. Even at this late date,
cattlemen leasing national land on the Western ranges demonstrate no more
than an ambivalent understanding, in constantly pressuring federal
authorities to increase the head count to the point where overgrazing
produces erosion and weed-dominance. Likewise, the oceans of the world
continue to suffer from the survival of the philosophy of the commons.
Maritime nations still respond automatically to the shibboleth of the
"freedom of the seas." Professing to believe in the "inexhaustible resources
of the oceans," they bring species after species of fish and whales closer to
extinction. [9]
The National Parks present another instance of the working out of the
tragedy of the commons. At present, they are open to all, without limit.
The parks themselves are limited in extent -- there is only one Yosemite
Valley -- whereas population seems to grow without limit. The values that
visitors seek in the parks are steadily eroded. Plainly, we must soon cease to
treat the parks as commons or they will be of no value to anyone.
What shall we do? We have several options. We might sell them off as
private property. We might keep them as public property, but allocate the
right to enter them. The allocation might be on the basis of wealth, by the
use of an auction system. It might be on the basis of merit, as defined by
some agreed璾pon standards. It might be by lottery. Or it might be on a
first-come, first-served basis, administered to long queues. These, I think,
are all objectionable. But we must choose -- or acquiesce in the destruction
of the commons that we call our National Parks.
Pollution
In a reverse way, the tragedy of the commons reappears in problems of
pollution. Here it is not a question of taking something out of the commons,
but of putting something in -- sewage, or chemical, radioactive, and heat
wastes into water; noxious and dangerous fumes into the air; and distracting
and unpleasant advertising signs into the line of sight. The calculations of
utility are much the same as before. The rational man finds that his share of
the cost of the wastes he discharges into the commons is less than the cost
of purifying his wastes before releasing them. Since this is true for
everyone, we are locked into a system of "fouling our own nest," so long as
we behave only as independent, rational, free enterprisers.
The tragedy of the commons as a food basket is averted by private property,
or something formally like it. But the air and waters surrounding us cannot
readily be fenced, and so the tragedy of the commons as a cesspool must be
prevented by different means, by coercive laws or taxing devices that make
it cheaper for the polluter to treat his pollutants than to discharge them
untreated. We have not progressed as far with the solution of this problem
as we have with the first. Indeed, our particular concept of private
property, which deters us from exhausting the positive resources of the
earth, favors pollution. The owner of a factory on the bank of a stream --
whose property extends to the middle of the stream -- often has difficulty
seeing why it is not his natural right to muddy the waters flowing past his
door. The law, always behind the times, requires elaborate stitching and
fitting to adapt it to this newly perceived aspect of the commons.
The pollution problem is a consequence of population. It did not much
matter how a lonely American frontiersman disposed of his waste. "Flowing
water purifies itself every ten miles," my grandfather used to say, and the
myth was near enough to the truth when he was a boy, for there were not
too many people. But as population became denser, the natural chemical
and biological recycling processes became overloaded, calling for a
redefinition of property rights.
How to Legislate Temperance?
Analysis of the pollution problem as a function of population density
uncovers a not generally recognized principle of morality, namely: the
morality of an act is a function of the state of the system at the time it is
performed. [10] Using the commons as a cesspool does not harm the general
public under frontier conditions, because there is no public; the same
behavior in a metropolis is unbearable. A hundred and fifty years ago a
plainsman could kill an American bison, cut out only the tongue for his
dinner, and discard the rest of the animal. He was not in any important
sense being wasteful. Today, with only a few thousand bison left, we would
be appalled at such behavior.
In passing, it is worth noting that the morality of an act cannot be
determined from a photograph. One does not know whether a man killing an
elephant or setting fire to the grassland is harming others until one knows
the total system in which his act appears. "One picture is worth a thousand
words," said an ancient Chinese; but it may take ten thousand words to
validate it. It is as tempting to ecologists as it is to reformers in general to
try to persuade others by way of the photographic shortcut. But the essence
of an argument cannot be photographed: it must be presented rationally --
in words.
That morality is system-sensitive escaped the attention of most codifiers of
ethics in the past. "Thou shalt not…" is the form of traditional ethical
directives which make no allowance for particular circumstances. The laws
of our society follow the pattern of ancient ethics, and therefore are poorly
suited to governing a complex, crowded, changeable world. Our epicyclic
solution is to augment statutory law with administrative law. Since it is
practically impossible to spell out all the conditions under which it is safe to
burn trash in the back yard or to run an automobile without smog璫ontrol,
by law we delegate the details to bureaus. The result is administrative law,
which is rightly feared for an ancient reason -- Quis custodies ipsos
custodes? --Who shall watch the watchers themselves? John Adams said that
we must have a "government of laws and not men." Bureau a