The Tragedy of the Commons
Garrett Hardin
At the end of a thoughtful article on the
future of nuclear war, Wiesner and York (1)
concluded that: “Both sides in the arms race
are . . . confronted by the dilemma of steadily
increasing military power and steadily de-
creasing 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.”
I would like to focus your attention not
on the subject of the article (national secu-
rity 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 de-
fined as one that requires a change only in
the techniques of the natural sciences, de-
manding 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. Be-
cause of previous failures in prophecy, it
takes courage to assert that a desired tech-
nical solution is not possible. Wiesner and
York exhibited this courage; publishing in a
science journal, they insisted that the solu-
tion to the problem was not to be found in
the natural sciences. They cautiously qual-
ified 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 identifica-
tion 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 keep-
ing 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 drug him; or I can
falsify the records. Every way in which I
“win” involves, in some sense, an aban-
donment of the game, as we intuitively
understand it. (I can also, of course, open-
ly 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 convention-
ally 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 relin-
quishing 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 steadily 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 popula-
tion 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? Specifical-
ly, 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 pur-
poses: mere maintenance and work. For
man, maintenance of life requires about
1600 kilocalories a day (“maintenance cal-
ories”). Anything that he does over and
above merely staying alive will be defined
as work, and is supported by “work calo-
ries” 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 max-
imize 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, with-
out 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 acquisi-
tion of energy that is the problem. The ap-
pearance 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 re-
placed 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 still
unobtainable.
The optimum population is, then, less
than the maximum. The difficulty of defin-
ing 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 wil-
derness, to another it is ski lodges for thou-
sands. 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 can-
not be compared.
The author is professor of biology, University of California,
Santa Barbara. This article is based on a presidential
address presented before the meeting of the Pacific Di-
vision of the American Association for the Advancement
of Science at Utah State University, Logan, 25 June
1968.
ARTICLE
www.sciencemag.org z SCIENCE z VOL. 162 z 13 DECEMBER 1968 1243–1248
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 incommensu-
rables. 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 deci-
sions 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 prac-
tical 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 rea-
sonable 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 exorcize 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 deci-
sions 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 individ-
ual fecundity so as to produce the optimum
population. If the assumption is not correct,
we need to reexamine our individual free-
doms to see which ones are defensible.
Tragedy of Freedom in a
Commons
The rebuttal to the invisible hand in popu-
lation control is to be found in a scenario
first sketched in a little-known pamphlet (6)
in 1833 by a mathematical amateur named
William Forster Lloyd (1794–1852). We
may well call it “the tragedy of the com-
mons,” using the word “tragedy” as the phi-
losopher Whitehead used it (7): “The es-
sence 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 inci-
dents 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 be-
cause 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 reckon-
ing, that is, the day when the long-desired
goal of social stability becomes a reality. At
this point, the inherent logic of the com-
mons remorselessly generates tragedy.
As a rational being, each herdsman seeks
to maximize his gain. Explicitly or implic-
itly, 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 11.
2) The negative component is a func-
tion 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 par-
ticular decision-making herdsman is only a
fraction of 21.
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; and another. . . . But this is the
conclusion reached by each and every ratio-
nal herdsman sharing a commons. Therein is
the tragedy. Each man is locked into a sys-
tem 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 inter-
est 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 re-
quires that the basis for this knowledge be
constantly refreshed.
A simple incident that occurred a few
years ago in Leominster, Massachusetts,
shows bow 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 in-
creased 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 agricul-
ture 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 fed-
eral authorities to increase the head count to
the point where overgrazing produces ero-
sion and weed-dominance. Likewise, the
oceans of the world continue to suffer from
the survival of the philosophy of the com-
mons. Maritime nations still respond auto-
matically 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 in-
stance 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 Yo-
semite Valley—whereas population seems
to grow without limit. The values that vis-
itors 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 op-
tions. 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
SCIENCE z VOL. 162 z 13 DECEMBER 1968 z www.sciencemag.org1243–1248
of wealth, by the use of an auction system.
It might be on the basis of merit, as defined
by some agreed-upon 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 the reason-
able possibilities. They are all objection-
able. 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 un-
pleasant 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 indepen-
dent, 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 un-
treated. 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 ex-
hausting the positive resources of the earth,
favors pollution. The owner of a factory on
the bank of a stream—whose property ex-
tends 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 10 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 func-
tion 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 impor-
tant sense being wasteful. Today, with only a
few thousand bison left, we would be ap-
palled 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 set-
ting 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 10,000 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 short-
cut. But the essense of an argument can-
not be photographed: it must be presented
rationally—in words.
That morality is system-sensitive es-
caped 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 fol-
low the pattern of ancient ethics, and there-
fore are poorly suited to governing a com-
plex, crowded, changeable world. Our epi-
cyclic solution is to augment statutory law
with administrative law. Since it is practi-
cally impossible to spell out all the condi-
tions under which it is safe to burn trash in
the back yard or to run an automobile with-
out smog-