text:
Κύρια Natural justice
Ken Binmore
This book lays out foundations for a "science of morals." Binmore uses game theory as a systematic tool for investigating ethical matters. He reinterprets classical social sontract ideas within a game-theory framework and generates new insights into the fundamental questions of social philosophy. In contrast to the previous writing in moral philosophy that relied on vague notion such as " societal well-being" and "moral duty," Binmore begins with individuals; rational decision-makers with the ability to emphasize with one another. Any social arrangement that prescribes them to act against their interests will become unstable and eventually will be replaced by another, until one is found that includes worthwhile actions for all individuals involved.
Categories: Mathematics\\Game Theory
Εκδότης: Oxford University Press, USA
The bounds of reason : game theory and the unification of the behavioral sciences
Herbert Gintis
Game Theory and the Social Contract, Vol. 1: Playing Fair
bargaining234
fairness182
nash144
isn134
societies126
adam and eve117
social contracts115
preferences113
empathetic111
equilibria102
bargaining solution100
payoffs84
rawls82
prisoners79
evolutionary76
dilemma76
payoff71
harsanyi70
egalitarian69
feasible63
hume61
enforcement61
empathetic preferences60
nash bargaining60
nash bargaining solution59
social indices56
interpersonal comparison53
utils53
coordination53
cooperation49
alice and bob48
bargaining problem46
philosophers46
external enforcement45
genes44
foraging44
equilibrium selection43
folk theorem42
kant42
empathy41
fairness norms40
utilities39
nash equilibrium36
tit35
tat35
reform35
Playing for Real
Does game theory work
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Natural justice / Binmore, K. G., 1940–
p.cm.
ISBN-13 978-0-19-517811-1
1. Justice. 2. Fairness. 3. Social ethics. I. Title.
JC578.B54 2004
320′.01′1—dc22 2004057639
is dedicated
to my son
In 1984, I impulsively accepted a late invitation to speak at a prestigious conference on social choice in Canada. Having
nothing relevant in my research file, I immediately set about throwing together a paper on a subject to which I had
previously given only an idle thought or two.
John Rawls' celebrated Theory of Justice proposes an imaginary scenario in which the citizens of a society meet to plan a
new social contract. Rawls suggests that the social contract on which they agree would be fair if the citizens are kept in
ignorance of their identities while bargaining. Each citizen will then have equal reason to fear being the victim of any
injustice built into the final deal. My idea was to apply Ariel Rubinstein's recently invented theory of rational bargaining
to the negotiation problem created by such a Rawlsian veil of ignorance.
Four weeks later, on the morning of my arrival at the conference, I presented a paper on this subject to a large
audience consisting almost entirely of strangers. After the talk, a tall gentleman rose from his seat, and introduced
himself as John Rawls. Given that I had been speaking more or less impromptu on a subject about which he knew a
great deal and I knew essentially nothing, his kindness went way beyond the call of duty—especially since I now know
that he had by then lost faith in economic theory as a tool for investigating political philosophy. However, his
continuing encouragement made me think it worthwhile to put my material into publishable form after tying up the
philosophical loose ends I had left blowing in the wind.
In 1994, I was still tying up loose ends, having come close to despair along the way, as attempt after attempt to create
adequate foundations for a scientific theory of fairness norms simply revealed new loose ends of whose existence I had
been unaware. Those who have grappled with Immanuel Kant will get some feeling for the immensity of the struggle,
when I say that I even read every book by Kant that was available in the library of the University of Michigan in an
attempt to get to the bottom of Rawls' assertion that he was merely operationalizing Kant's categorical imperative. But
this effort was to prove my salvation. It eventually dawned upon me that I was reading the work of an emperor who
was clothed in nothing more than the obscurity of his prose.
Kant never provides any genuine defense of his claims—not even in his Grundwerke. His categorical imperative is
simply a grandiloquent rendering of the folk wisdom which says that it is immoral to lay oneself open to my mother's
favorite reproach: "Suppose everybody behaved liked that?" Kant's assertion that one should
honor this principle for rational reasons is conjured from the air. But Kant is widely regarded as the greatest
philosopher of all time. Could it really be that his claim to fame as a moral philosopher is based merely on his having
invented one of the fallacies of the Prisoners' Dilemma before anyone else?
If I hadn't once held the chair in mathematics at the London School of Economics, and so had the opportunity to
interact a little with Karl Popper, I would probably have rejected this suggestion as being too outrageous to consider
seriously. I can't say that I found Popper's manner very charming, but one has only to read his quotes from Plato's
Republic to recognize that Popper's Enemies of the Open Society is right on the ball in denying that the received opinion of
Plato as the founder of rational liberalism can be squared with what Plato actually believed. In modern terms, Plato
was a fascist who thought that we all so need a leader that nobody should even "get up, or move, or wash, or take his
meals" without permission! If philosophical scholarship could convert such adolescent authoritarianism into a model
of civilized debate, might it not have done the same for Kant's attempts to evade the rules of deductive reasoning?
My mathematical friends and colleagues were of no help, because their training in logic had led them to abandon Kant
much sooner than I. So I began to approach philosophers with my heretical thoughts. Those willing to talk to me fell
into three classes. Philosophers in the first class agreed that the categorical imperative calls for cooperation in the
Prisoners' Dilemma, and dismissed game theory as misguided and irrelevant. Those in the second class explained that
Kant's conception of a maxim and a universal law are too subtle to allow a definite yes or no as to whether it is rational
to cooperate in the Prisoners' Dilemma. However, I struck gold with philosophers in the third class, who told me to
read the works of David Hume.
I can't say that I realized immediately that I was reading the author who genuinely deserves to be called the greatest
philosopher of all time. Like most people, I allowed the fact that he is one of the great stylists of the English language
to cloud my appreciation of his creative genius. As though merely making conversation, he would today be explaining
quantum physics to someone he met on a bus without either party feeling any sense of incongruity. But the tendency to
assess the quality of a good by its price carries over into philosophy. Surely the hours spent struggling to make sense of
Kant must be a measure of the depth and originality of his thought? How could the insights bought at such a low price
from Hume be comparable in value?
However, a game theorist ought to have recognized from the start that Hume is the original inventor of reciprocal
altruism—the first person to recognize that the equilibrium ideas now studied in game theory are vital to an
understanding of how human societies work. He understood that one must look to evolution for a solution of the
equilibrium selection problem—a conclusion that modern game theorists have reached only after fifty years of fruitless
attempts to tackle the difficulty by inventing high-flown definitions of rationality in the style of Kant. He even
anticipated modern game theorists in seeing legal reform as a problem in mechanism design.
Reading Hume gave me the courage to throw off the dead hand of Kantian metaphysics and to seek naturalistic
foundations for Rawls' powerful intuitions about the way human fairness norms work. My background as a
mathematician-turned-economist
seemed to put me in an ideal position to translate his pregnant thoughts into simple mathematical models using the
language of game theory invented by Von Neumann and Morgenstern.
The time was particularly apt, since Hamilton, Maynard Smith, and others had also recently applied the language of
game theory to evolutionary biology, and so made it possible to understand the role of the family in the evolution of
human morality. For a long time, I was held up by the necessity of coming up with a theory of interpersonal
comparison of utility, but this problem eventually solved itself when I realized that Rawls' egalitarian theory wasn't so
distant as it looked fromthe utilitarian theory of John Harsanyi. Once Harsanyi's metaphysical theory of interpersonal
comparison had been reinterpreted in naturalistic terms, and then recycled through a Rawlsian filter, I was led to a
formulation of fairness that is very close to the psychological law of equity, for which a measure of empirical support
has been obtained in the laboratory.
Putting this material into publishable form proved a nightmare. Nearly everything I had to say was controversial to
somebody, and it was therefore necessary to be very precise about the basic framework. But how can one explain
things in precise terms to people who are untrained in mathematics? In the end, I compromised by writing a twovolume work for MIT Press called Game Theory and the Social Contract that contains long expository passages but makes
free use of formulas and equations, although I did the best I could to keep them to a minimum.
The first volume, Playing Fair, which appeared in 1994, attempted to clear the air by expounding the widely
misunderstood ideas from economic theory that I needed to call upon. For example, the third chapter lists all the
fallacies of the Prisoners' Dilemma that I had come across at that time, explaining in detail the various errors in
reasoning involved. A long delay then ensued before the second volume Just Playing appeared in 1998 with the beef of
the theory. Between the publication of the two volumes, I read so much anthropology, biology, economics, philosophy,
and psychology that my previous reading of Kant's works pales into insignificance by comparison. The experience was
immensely rewarding, but I have to confess to times when my heart sank as I realized that there was yet another whole
literature of which I knew nothing at all.
Not being sufficiently original to fall "deadborn from the press" like David Hume's first great work, my Game Theory
and the Social Contract sold reasonably well. But it isn't a book for the general reader. It is an academic work with long
footnotes and earnest asides considering abstruse objections. As always in such books, it discusses much literature of
marginal relevance in the hope of disarming critics who would otherwise challenge its author's scholarly credentials.
Worst of all are the equations—each of which halves a book's readership, if Stephen Hawking is to be believed.
Natural Justice has been written to try to bring my ideas to a wider audience. The previous publication of Game Theory
and the Social Contract leaves me free to adopt the conventions of popular science books without feeling too guilty. In
Natural Justice, I don't hedge my speculations about with reservations and qualifications. My claims aren't proved, but
illustrated with examples. Scholarly references are rare. Above all, there are no algebraic equations at all. If Hawking is
right and
my audience doubles for each equation removed from Game Theory and the Social Contract, I shall be the most successful
author of all time!
But I will be satisfied if Natural Justice is able to make at least some converts to the view that debate on public morality
and political reform needn't be confined to those would-be philosopher-kings who continue to write footnotes to
Plato. Two thousand years of such moral punditry has got us nowhere, and never will. Surely we now know enough
about human nature to begin to restrict our attention to aspirations for our societies that have some chance of working.
Finally, I want to thank all the many people who have helped me with this book, especially John Weymark and Terry
Vaughn, whose faith in the project was a constant source of comfort and support.
Monmouth, Wales
1 Moral Science
1.1 Evolutionary Ethics
1.2 Mudslinging
1.3 Social Contracts
1.4 Stability
1.5 Efficiency
1.6 Fairness
1.7 Reform
2 Bargaining
2.1 Realistic Bargaining
2.2 The Meeting Game
2.3 Bargaining Problems
2.4 The Nash Bargaining Solution
2.5 Interpersonal Comparison of Utility
2.6 Social Indices
2.7 The Utilitarian Bargaining Solution
2.8 The Egalitarian Bargaining Solution
2.9 Utilitarianism versus Egalitarianism
2.10 Enforcement
2.11 Cultural Evolution
2.12 Signifying Nothing?
3 Battle of the Isms
3.1 Kicking up Dust
3.2 Empiricism
3.3 Naturalism
3.4 Relativism
3.5 Reductionism
3.6 Nil desperandum!
4 Equilibrium
4.1 Inventing Right and Wrong
4.2 Toy Games
4.3 Cooperation and Conflict
4.4 Mixed Strategies
4.5 The Prisoners' Dilemma
4.6 Multiple Equilibria
4.7 Nash Demand Game
4.8 Out-of-Equilibrium Behavior
5 Reciprocity
5.1 Tit-for-Tat
5.2 Folk Theorem
5.3 Punishment
5.4 Quis custodiet ipsos custodes?
5.5 Emergent Phenomena
5.6 Unpleasant Behavior
5.7 Free for All?
6 Duty
6.1 The Good, the Right and the Seemly
6.2 Rights
6.3 Dressing Up
6.4 Moral Responsibility
7 Kinship
7.1 Sympathy
7.2 Kin Selection
7.3 Social Insects
7.4 Modifying Hamilton's Rule?
7.5 Learning to Play an Equilibrium
7.6 Extending the Family
7.7 Warm Glow
8 Empathy
8.1 Empathetic Preferences
8.2 Empathetic Identification
8.3 Utility
8.5 The Evolution of Empathetic Preferences
9 The Golden Rule
9.1 Sages down the Ages
9.2 Hunters and Gatherers
9.3 Mechanism Design
9.4 An Origin for the Golden Rule?
9.5 Enforcement
10 Utilitarianism
10.1 John Harsanyi
10.2 Skyhooks?
10.3 Summum Bonum?
10.4 Political Legitimacy
10.5 Bargaining in the Original Position
10.6 Social Evolution
10.7 How Utilitarian Justice Works
10.8 A Food-Sharing Example
10.9 Relativity
10.10 Why Not Utilitarianism?
11 Egalitarianism
11.1 Original Sin
11.2 Equity
11.3 Rawls' Difference Principle
11.4 The Phantom Coin
11.5 Fair Social Contracts
11.6 How Egalitarian Justice Works
11.7 Trustless Transactions
11.8 Social Indices and the Context
11.9 The Market
12 Planned Decentralization
12.1 A Third Way?
12.2 Whiggery
12.3 Why Decentralize?
12.4 Why Plan?
12.5 Designing a Social Mechanism
12.6 Reforming a Social Contract?
12.7 Unfinished Business
12.8 A Perfect Commonwealth?
Chapter 1 Moral Science
He who understands Baboon would do more towards metaphysics than John Locke.
II:2.4
What should we be aiming for? Wherein lies our duty? How ought we to live? Such questions have been debated for
millenia, but to so little effect that moral philosophers commonly agree that the sum of their endeavors should count
as no more than a footnote to Plato. How could so little have been achieved in such a long time?
I think that orthodox moral philosophy has gotten nowhere because it asks the wrong questions. If morality evolved
along with the human race, then asking how we ought to live makes as much sense as asking what animals ought to
exist, or which language we ought to speak.
The authority claimed by gurus who argue to the contrary is conjured from nowhere. They no more have access to
some noumenal world of moral absolutes than the boy who delivers our newspapers. Like the rest of us, they actually
get their intuitions from observing the real rules that govern our moral behavior. These are not the absurdly impractical
moral principles we teach to our children, but which they quickly learn to classify alongside Santa Claus and the Tooth
Fairy. As every parent knows, it is a waste of time preaching to children unless you also practice what you preach.
The moral rules that really govern our behavior consist of a mixture of instincts, customs, and conventions that are
simultaneously more mundane and more complex than traditional scholarship is willing to credit. They are shaped
largely by evolutionary forces—social as well as biological. If one wishes to study such rules, it doesn't help to ask how
they advance the Good or preserve the Right. One must ask instead how they evolved and why they survive. That is to
say, we need to treat morality as a science.
The idea that morality is best understood from an evolutionary perspective goes all the way back to Charles Darwin,
but progress in developing this most controversial of his many insights has been painfully slow. People are so reluctant
to surrender traditional ways of thinking about morality that they actively place obstacles in the path of those who are
more adventurous by ridiculing or misrepresenting their views.
This task was made easier by the appearance of an early school of would-be moralists who argued that the strong
ought to be allowed to trample on the weak because only the fit survive. The philosopher Moore lampooned their
views as the proposition that "we ought to move in the direction of evolution simply because it is the direction of
evolution". Although the idea that Darwinism is teleological is manifestly absurd, their unpleasant creed is nowadays
called Social Darwinism in an attempt to discredit anyone who uses the words evolution and ethics in the same
sentence. Critics of Edward Wilson's Sociobiology contrived to sling this kind of mud so successfully that some of his
followers now prefer to call themselves behavioral ecologists or evolutionary psychologists rather than stand accused
of being sociobiological fascists.
The same eggshell sensitivity to mudslinging is also to be found in the popular books on evolutionary theory that are
now endemic in airport bookstores. Such books commonly present the evidence that our minds and bodies evolved
from less complex organisms with such consummate skill that one has to doubt the sincerity of the dwindling band of
brothers who continue to insist that evolution is just a theory. However, when it comes to evolutionary ethics, the
eloquence of popular authors dries up, and all we usually get on the subject is a few inoffensive platitudes toward the
end of the last chapter.
Even if I wanted to, there is no way that I can similarly walk on eggshells. If I am taken seriously, I know that I will
therefore be attacked from all sides as an ignorant teller of just-so stories. It is true that one can't write about human
morality with the same authority as the life cycle of the parasitic worm Dicrolium dendriticum or the leaf-cutting ant
Acromyrmex versicolor, but the importance of the subject surely licenses a certain amount of informed speculation. After
all, nobody complains when cosmologists speculate that most of the universe consists of dark energy and matter of
which we have no direct evidence at all. So why should similar theorizing be forbidden when studying morality? Only, I
think, because moral and religious zealots see it as a challenge to their spurious sources of authority.
In any case, I plan to brave the inevitable brickbats by taking the basic facts of evolution for granted, and devoting the
whole of this book to a sustained line of speculation on the evolutionary origins of the human fairness norms that lie at
the root of our notions of justice.
My past efforts in this direction have all involved mathematical modeling, but there is no algebra in this book. Nor is
there any heavy philosophizing. Nor yet scholarly references and learned asides on why I differ from others. My plan is
to get on with telling my story with as few apologies as possible. Anyone sufficiently interested can look for
documentation in my two-volume Game Theory and the Social Contract, to which the marginal notes refer.
I:1.2.3
A social contract is the set of common understandings that allow the citizens of a society to coordinate their efforts.
The common understandings or conventions that make up a social contract are many and various. They range from
the arcane table manners we employ at formal dinner parties to the significance we attach to the green pieces of paper
we carry round in our wallets bearing pictures of past presidents. From the rules that govern how we drive our cars in
heavy traffic to the meaning of the words in the language we speak. From dietary and sexual taboos to the standards of
integrity and truthfulness expected of honorable folk. From the vagaries of fashion to the criteria that we fondly
suppose secure ownership of our possessions. From the amount that we think it appropriate to tip in restaurants to the
circumstances under which we are ready to submit ourselves to the authority of others.
The seemingly profound half of each of these pairings is usually attributed to iron laws of morality derived from an
ineffable source into which we are not encouraged to look too closely. But I think the differences between the trivial
and the profound halves in the pairings are differences only of degree. There are no iron laws beyond those encoded in
our genes. Like Gulliver in Lilliput, we are bound only by a thousand gossamer threads woven from our own beliefs
Everybody believes this of fashion and etiquette, where it is necessary that the rules change sufficiently fast that
outsiders are always just far enough behind that they can be distinguished from insiders. There are those who would
claim otherwise of dietary taboos, but most of us know perfectly well that we would be as unwilling to eat a cow or a
pig if we had been brought up in another society as we currently are to eat a dog or a caterpillar. Sexual mores are
particularly fluid. In Nigeria, a woman guilty of adultery can be stoned, whereas a chaste woman in Beverly Hills would
be at risk of social exclusion if found out.
The same goes for the different standards of honesty and fair play that operate in different societies. The myth that
there are universal standards doesn't even begin to hold water. We even think it right to operate different standards
ourselves in different contexts. Would you, for example, blow the whistle on a colleague if you learned that he was
cheating on his tax returns? But what if he had falsified his results in reporting a scientific experiment?
It is true that some of our cultural conventions are codified as laws, but the legal system and the constitution of a
modern society are relevant to a social contract only to the extent that they are actually honored in practice. If it is
customary to give and take bribes, then giving and taking bribes is part of the social contract—whatever the law may
As for the authority of constitutions, all of us would be delighted to enjoy the civil rights supposedly guaranteed by the
constitution of the old Soviet Union. Nor are popes, presidents, kings, judges, or the police exempt from the social
contract of the society in which they officiate. Far from enforcing the social contract, they derive what power they have
from a social convention which says that ordinary citizens should accept their direction. If they were ignored in the
same way that the citizens of Naples ignore traffic signals, they would be totally powerless.
How Do Social Contracts Work?
What is the glue that holds a society together? It isn't the law or the constitution. These are just words on a piece of
paper. It isn't the officers of state. They are just people like you or me. Is it our sense of moral obligation? But there is
honor of a sort even among thieves. Is it God? Some social contracts are so horrendous that even fundamentalists
must sometimes entertain doubts.
None of these answers fit the bill, because we asked the wrong question. A stable social contract doesn't need any glue.
Dostoyevsky's autobiographical House of the Dead makes this point very clearly when describing his experience as a
political prisoner in a Czarist concentration camp: "The majority of these men were depraved and hopelessly corrupt.
The scandals and the gossip never ceased; this was a hell, a dark night of the soul. But no-one dared to rebel against
the endogenous and accepted rules of the prison; everyone submitted to them. To the prison came men who had gone
too far . . . the terror of whole villages and towns . . . [but] the new convict . . . imperceptibly grew resigned and fitted in
with the general tone." Dostoyevsky's fellow convicts didn't follow the social contract that had evolved in the camp for
moral reasons, or because they feared the prison guards. They unknowingly followed its precepts because their fellow
prisoners punished them if they didn't.
When punishment is mentioned, one's mind naturally turns to the kind of institutionalized violence that put
Dostoyevsky behind bars in the first place. But the punishments that deter us from cheating on the social contract are
nearly always so mild that we scarcely notice them at all. In my own country, I find it hard to codify the subtle use of
body language and shades of verbal expression that my neighbors use to hint that my current behavior is likely to result
in more positive forms of social exclusion if I don't start mending my ways. One is so habituated to responding
appropriately, that such subliminal signals are automatically translated into behavior without any conscious control.
Only when some social gaffe in a foreign country is greeted by an unfamiliar signal does the mechanism become
apparent.
In David Hume's metaphor, a social contract holds together like a drystone wall or a masonry arch. Each stone
supports and is supported by its neighbors, without any need for cement or glue. In modern game theory, we express
the same idea by saying that the rules of a stable social contract succeed in coordinating our behavior on an equilibrium
in the game of life. With this idea under our belts, we can give up the search for the social equivalent of the angels
invented by medieval philosophers to explain what keeps the planets in their orbits. Like the solar system, our societies
work all by themselves.
Much of this book explores the consequences of David Hume's insight that a social contract can be seen as a largely
unrecognized consensus to coordinate on a particular equilibrium of the game of life that we play together. As Hume
explains: "Two men, who pull the oars of a boat, do it by an agreement or convention, tho' they have never given
promises to one another. Nor is the rule concerning the stability of possessions the less derived from human
conventions, that it arises gradually, and acquires force by a slow progression . . . In like manner are languages
gradually established by human conventions without any promise. In like manner do gold and silver become the
common measures of exchange."
So what is an equilibrium? How does it capture Hume's big idea? How come a society finds itself at one equilibrium
rather than another?
Writing on this subject is like juggling with numerous slippery balls while being pelted with rotten vegetables by a surly
audience. Critics are particularly impatient at the necessity of getting the balls in the air one at a time. Whatever ball
they are first shown is taken to be the whole of the theory, which can then be dismissed as naive on the grounds that it
doesn't take account of all the other balls.
In this chapter and the next, I try to head off such hasty criticism by giving broad-brush answers to some of the more
immediate broad-brush questions in the course of distinguishing three levels of priority made necessary by an
evolutionary approach to social contract theory. The three levels of priority are:
Efficiency
A social contract must be internally stable, or it won't survive. It needs to be efficient, or it won't compete successfully
with the social contracts of other societies. Conventional moral philosophy pays little or no attention to either of these
issues, but we shall find that they are essential to making sense of the question that arises at the third level: How and
why are social contracts fair?
I know that the danger in beginning a book with such an extended introduction is that critics will assume that I am
unable to provide a detailed defense of the claims that are being made. However, these details are provided in later
chapters as I work up through the three levels of priority, justifying the claims made in the current overview along the
way. Some patience is therefore necessary on the part of those who don't think that it possible that social justice can
have a natural origin, since I only really get going on this subject in chapter 9.
I:2.2
After the movie A Beautiful Mind, everybody has heard of John Nash, who was awarded a Nobel prize after recovering
from a schizophrenic illness that left him on the sidelines of intellectual inquiry for more than forty years. He got his
prize both for his work on bargaining theory, and for formulating the idea of an equilibrium in a game. The movie
makes a feeble attempt to give an example of a Nash equilibrium, but gets it hopelessly wrong, although the basic idea
isn't hard to understand.
A game is any situation in which people or animals interact. The plans of action of the players are called strategies. A
Nash equilibrium is any profile of strategies—one for each player—in which each player's strategy is a best reply to the
strategies of the other players.
A very simple example is the Driving Game we play each time we get into our cars in the morning to drive to work.
Shall we drive on the left or on the right? If all we care about is avoiding accidents, the game has three Nash equilibria.
In the first, we all choose the strategy of driving on the left. In the second, we all choose the strategy of driving on the
right. In the third, we each toss a coin to
decide whether to drive on the left or on the right. The third alternative may seem dubious, but if everybody else is
randomizing their choice, your chances of ending up in an accident are going to be the same whatever you do. So
tossing a coin is just as much a best reply as doing anything else.
Why should anyone care about Nash equilibria? There are at least two reasons. The first is that if a game has a rational
solution that is common knowledge among the players, then it must be an equilibrium. If it weren't, then some of the
players would have to believe that it is rational for them not to make their best reply to what they know the other
players are going to do. But it can't be rational not to play optimally.
The second reason why equilibria matter is even more important. If the payoffs in a game correspond to how fit the
players are, then evolutionary processes—either cultural or biological—that favor the more fit at the expense of the
less fit will stop working when we get to an equilibrium, because all the survivors will then be as fit as it is possible to
be in the circumstances.
Much of the power of game theory as a conceptual tool derives from the possibility of moving back and forward
between the rational and evolutionary interpretations of an equilibrium. Since this is an idea which is easily
misunderstood, the first priority is to explain why switching interpretations in this way can be legitimate.
Selsh Genes?
Because evolution stops working at an equilibrium, biologists say that Nash equilibria are evolutionarily stable.1 Each
relevant locus on a chromosome is then occupied by the gene with maximal fitness. Since a gene is just a molecule, it
can't choose to maximize its fitness, but evolution makes it seem as though it had. This is a valuable insight, because it
allows biologists to use the rational interpretation of an equilibrium to predict the outcome of an evolutionary process,
without following each complicated twist and turn that the process might take.
The title of Richard Dawkins' Selfish Gene expresses the idea in a nutshell, but it also provokes a lot of criticism. It is
easy to be tolerant of critics like the old lady I heard rebuking Dawkins for failing to see that a molecule can't possibly
have free will, but tolerance is less easy in the case of critics like Lewontin or Gould, who chose to whip up public
hostility against Edward Wilson and his followers on similar grounds. As Alcock's Triumph of Sociobiology documents,
they willfully pretend not to understand that sociobiologists seek explanations of biological phenomena in terms of
ultimate causes rather than proximate causes.
Why, for example, do songbirds sing in the early spring? The proximate cause is long and difficult. This molecule
knocked against that molecule. This chemical reaction is catalyzed by that enzyme. But the ultimate cause is that the
birds are signalling territorial claims to each other in order to avoid unnecessary conflict. They neither know nor care
that this behavior is rational. They just do what they do. But the net effect of an immensely complicated evolutionary
process is that songbirds behave as though they had rationally chosen to maximize their fitness.
John Maynard Smith defines an evolutionarily stable strategy (ESS) to be a best reply to itself that is a better reply to any alternative best reply than the alternative best reply is
to itself, but biologists seldom worry about the small print involving alternative best replies.
When studying the social behavior of songbirds and other animals, evolutionary biologists seldom know any more
about the proximate causes of what they observe than the animals themselves. But only the most prejudiced critic can
deny them the successes they have enjoyed in explaining social behavior in terms of ultimate causes in the manner dear
to the hearts of game theorists.
1.5 Efciency
The first priority for a social contract is stability, which is to be crudely modeled using the idea of an equilibrium in a
game. The next priority is efficiency, which means that nothing gets wasted. Economists follow Vilfredo Pareto in
taking the absence of waste to be equivalent to the requirement that nobody can be made better off without someone
else being made worse off.
Adam Smith famously explained that an "invisible hand" steers a perfectly competitive market to an efficient outcome.
This invisible hand is yet another metaphor like the selfish gene. What actually happens is that sellers from whom
people are reluctant to buy gradually lower the prices at which they are willing to sell, and buyers to whom people are
reluctant to sell gradually raise the price at which they are willing to buy. When this process stops, there is no waste,
because demand equals supply. No genes compete for survival in such economic adjustment processes, but I shall still
call them evolutionary, because they work by themselves, without planning or supervision, until an equilibrium is
Traditional economists sometimes forget that perfectly competitive markets are the exception rather than the rule, and
hence come on as though we should expect the equilibria of all the games that people play with each other to be
efficient.2 But this is very far from the truth.
The Tragedy of the Commons is a stylized game that illustrates why equilibria are often inefficient. A hundred families
keep goats that graze on some common land. Total milk production is maximized with a thousand goats in all. How
many goats should each family keep to maximize its own milk production?
At first sight, the answer seems to be ten, but it isn't an equilibrium for each family to keep ten goats. If all the other
families keep ten goats, your family's optimal strategy isn't to do the same. You will do better by grazing one goat
more, because your family will enjoy all the benefit from the extra goat, while its cost in terms of less grass for the
other goats to eat will be shared by the whole community. Families will therefore add extra goats to their herd until the
common is reduced to a desert. But this outcome is very inefficient indeed.
The Tragedy of the Commons captures the logic of a whole spectrum of environmental disasters that we have brought
upon ourselves. The Sahara Desert is relentlessly expanding southward, partly because the pastoral peoples who live
on its borders persistently overgraze its marginal grasslands. We jam our roads with
For competition to be perfect, a whole list of conditions must be satisfied, even when frictions in the adjustment process are ignored. We need a large numbers of buyers and
sellers, none of whom is big enough to have market power on their own. Nobody must have any secrets. Returns to production need to be decreasing. And so on.
cars. We poison our rivers and pollute the atmosphere. We fell the rainforests. We have plundered our fisheries until
some fish stocks have reached a level from which they may never recover.
Game theorists get a lot of stick for saying this kind of thing. Our critics ask how it can possibly be rational for a society
to engineer such disasters. Can't we see that everybody would be better off if everybody were to grab less of the
common resource? The error in this kind of reasoning is elementary. A player in the human game of life isn't some
abstract entity called "everybody". We are all separate individuals, each with our own aims and purposes. Even when
our capacity for love moves us to make sacrifices for others, we each do so in our own way and for our own reasons.
In biology, the mistake of confusing the aims of individuals with aims attributed to the collectives of which they form a
part is called the group selection fallacy. One can't help feeling sorry for the biologist Wynne-Edwards, who is endlessly
denounced for originating the fallacy, but it can't be right that genes will be favored that benefit the survival of the
species at the expense of their own fitness. For example, starlings don't flock together in the evenings to estimate their
numbers in order that each starling can selflessly restrict its breeding opportunities so as to keep the population at an
optimal level. If they did, mutant starlings programmed to take advantage of the chastity of their fellows by breeding
without restraint would soon predominate.
Reciprocal Altruism.
The invisible hand can only be counted on to take a population to an efficient outcome of a game in the exceptional
case when all of its equilibria happen to be efficient. Perfectly competitive markets are one such case, but markets
didn't exist when our species separated itself from the other apes. So how did our unique style of cooperation evolve?
Because relatives share genes, it is easy to explain the evolution of cooperation within the family. For example, any of
my genes has half a chance of being present in the body of my sister. If I were genetically programmed to maximize
the average number of copies of my genes that are transmitted to the next generation, I would therefore count each of
my sister's children as being worth half of one of my own. This is presumably why some birds help bring up their
nephews and nieces when their own chances of raising a family are not very promising.
But human cooperation is more complex. The fierce loyalties that sometimes develop in street gangs or army platoons
can perhaps be explained in terms of the collective serving as a surrogate family, but we often manage to cooperate
very successfully with total strangers, or with people whom we actively dislike or despise. What is the secret of this
seeming contradiction to the doctrine of the selfish gene?
In 1976, Robert Trivers offered "reciprocal altruism" as the solution of the mystery, but David Hume was already on
the ball in 1739.
As Hume explains: "I learn to do service to another, without bearing him any real kindness, because I foresee, that he
will return my service in expectation of another of the same kind, and in order to maintain the same correspondence
of good offices with me and others. And accordingly, after I have serv'd him and he is in possession of the advantage
arising from my action, he is induc'd to perform his
part, as foreseeing the consequences of his refusal."
Vampire bats provide an exotic example of reciprocity in action. The bats roost in caves in large numbers during the
day. At night, they forage for prey, from whom they suck blood if they can, but they aren't always successful. If they fail
to obtain blood for several successive nights, they die. The evolutionary pressure to share blood is therefore strong.
The biologist Wilkinson reports that a hungry bat begs for blood from a roostmate, who will sometimes respond by
regurgitating some of the blood it is carrying in its own stomach. This isn't too surprising when the roostmates are
related, but the bats also share blood with roostmates who aren't relatives. The behavior is nevertheless evolutionarily
stable, because the sharing is done on a reciprocal basis, which means that a bat is much more likely to help out a
roostmate that has helped it out in the past. Bats that refuse to help out their fellows therefore risk not being helped
out themselves in the future.
Although vampire genes are selfish, reciprocal sharing turns out to be sustainable as an equilibrium in the vampire
game of life. We therefore don't always need to assume that people are selfless to explain cooperation in the human
game of life. A society of Mr. Hydes can use reciprocal altruism to sustain an efficient social contract just as effectively
as a society of Dr. Jekylls. We may not like their motives for avoiding waste, but it is enough for a social contract to be
efficient that waste is avoided.
Warm Glow?
To say that reciprocal altruism is important to the survival of human social contracts is usually taken as a wicked denial
of the existence of selfless altruism, so let me insist that I too derive a warm glow from my occasional selfless acts. I
give money to charity like other bourgeois folk. If I could swim better, perhaps I would be one of those who are willing
to risk their lives by plunging into a raging torrent to save a stranger from drowning.
However, it is necessary to face up to the fact that such selfless altruism survives because it either doesn't cost us very
much, or else is called for only rarely. Apart from a few saints, who gives so much of their income to charity that it
really hurts? Who would keep on plunging into the river if there were always a stranger struggling for his life when you
took the dog out for a walk? If taxes were replaced by voluntary contributions, how would the resulting Tragedy of the
Commons eventually get played? If there were no policemen, who would walk safe at night?
We are all mixtures of the selfless Dr. Jekyll and the selfish Mr. Hyde. It would be nice if human nature had more Jekyll
and less Hyde, but no amount of abusing sociobiologists is going to change what evolution has made of us. History is
full of failed utopias in which Jekyll was going to displace Hyde as soon as the conditions were right. If we are to avoid
repeating these mistakes, we need to be realistic about the relative amounts of Jekyll and Hyde that are mixed into the
human cocktail.
I was brought up in a tough neighborhood that taught me not to rely very much on the milk of human kindness.
Outside my immediate circle, there was a lot of Hyde and not much Jekyll. Most of those who read this book will have
been luckier, and grown up with a gentler social contract. But everybody can read about the
downside of human nature in newspapers and history books.
Who were those southern gentlemen who once got their kicks from lynching uppity blacks? What of the ordinary
German housewives who turned to savagery when recruited as guards at Ravensbrück? How about the subjects in
Milgram's experiments who inflicted apparently painful electric shocks on a helpless victim when told to do so by an
authority figure? Those people are us—or who we might have been if we had lived their lives in their cultures. Perhaps
you or I would have been one of the brave exceptions, but who would want the survival of our social contract to rely
on this being true of everybody?
The Folk Theorem.
Game theorists don't talk about altruism at all when discussing reciprocity. Perhaps this explains why the world paid
no attention to their discovery of the secret of how reciprocal altruism works some twenty-five years before Trivers
introduced the idea to biologists. This secret seemed so obvious after John Nash's formulation of an equilibrium in the
early fifties that nobody knew to whom the idea should be attributed. It is therefore called the folk theorem.
Rational reciprocity can't work unless people interact repeatedly, without a definite end to their relationship in sight. If
the reason I scratch your back today is that I expect you will then scratch my back tomorrow, then our cooperative
arrangement will unravel if we know that there will eventually be no tomorrow.
The simplest kind of game in which reciprocity can appear is therefore a repeated game with an indefinite time horizon.
The simplest of the folk theorems characterizes all the equilibria of such a game in the case when nobody can conceal
any information, and everybody always cares about tomorrow nearly as much as they care about today. The important
point is that any efficient outcome of the original game on which the players might like to agree approximates an
equilibrium outcome of the repeated game.
For example, in the Tragedy of the Commons, the efficient outcomes are those in which exactly one 1,000 goats graze
the common. If the 100 families got together in a conclave, they might agree on what share of the 1,000 goats each
family should be allowed to keep. But without an external enforcement agency to police the deal, it won't hold
together, because nothing prevents a family cheating on the deal by keeping more goats than they were assigned at the
conclave.
But if the Tragedy of the Commons is repeated indefinitely often, the folk theorem says that the deal reached at the
conclave can be sustained as a self-policing social contract. In equilibrium, no family will try to improve their lot by
cheating on the deal today, because they see that other families will respond by nullifying today's gain in the future.
In later chapters, we shall find that the folk theorem improves on David Hume's insight that a social contract is like a
masonry arch or a drystone wall by allowing us to examine the details of the equilibrium strategies that sustain it. We
can thereby break with the tradition that takes concepts like authority, duty and trust as axiomatic when explaining social
contracts, and see them rather as words that have evolved to describe different social contracts.
For example, it is fashionable nowadays to attribute our current social woes to
a lack of the "social capital" our grandparents enjoyed. The implication is that the cure is to inject more social capital
into the body politic. But looking around for more social capital is like sending a rookie out for a pint of elbow grease.
Social capital isn't a thing—it's just a word we use when talking about the properties of an equilibrium that has evolved
along with our game of life. Similarly, if we want to know why a citizen obeys an officer of the state, it isn't an
explanation to say that the citizen respects the authority of the officer. One might as well say that the stones in a
masonry arch stay where they are because they don't move.
Just as it is held to be wicked to say that cooperation is possible without people acting selflessly, so the idea that the folk
theorem can explain the workings of supposedly difficult ideas like authority, duty, and trust is held to be naive. Let me
therefore hasten to explain that nobody thinks that the ways these notions operate in any given social contract are
simple. The detailed workings of real social contracts are complex beyond our capacity to imagine. But traditional
moral pundits are too busy making easy things difficult to come anywhere near addressing these fundamental issues.
They are right that it would be naive to think that the folk theorem teaches us more than one small secret about human
sociality, but we shall find that only one small secret is needed to settle much of the dust that these same pundits kick
around so furiously.
Evolution of Cooperation.
II:3.3.8
Darwin commented on our similarity to baboons. More recently, chimpanzees have been recognized as closer cousins.
Not only do we share nearly all our genes, but we also behave like chimpanzees in many respects. De Waal's Good
Natured even offers convincing evidence that chimpanzees empathize with each other, putting themselves in the
position of their fellows to see things from their point of view. The foundation stones for our sense of justice must
therefore have been in place long before humans appeared on the scene.
Such relevations about chimpanzees and other primates have led some authors to insist that humanity is nothing more
than another species of ape. This is a natural reaction to the popular Cartesian claim that we are somehow endowed
with a divine spark that elevates us above mere automata like dogs and cats. But to adopt a perspective that minimizes
the distinctions between us and other animals is to abandon any hope of explaining the gulf between the sharing of
food that is common in chimpanzee societies and the extreme egalitarianism of some of the human hunter-gatherer
bands that survived into modern times.
We are indeed naked apes, but it doesn't follow that the way to find out about human table manners is to watch
baboons dining. Our brains are also pieces of biological machinery, but we won't learn French by listening to a vacuum
cleaner. Like etiquette and language, justice is exclusively a human phenomenon. To understand it, we need to pay as
much or more attention to what makes us different from other animals as to what makes us the same. I think that part
of the answer lies in the unique ability of our species to use culture as a means of solving equilibrium selection
Games commonly have many equilibria. For example, the Driving Game has three. The equilibrium in which
everybody drives on the left and the equilibrium
in which everybody drives in the right are both efficient. The equilibrium in which people decide on which side of the
road to drive at random is inefficient, because everybody could get a higher payoff by driving on the same side of the
Such a multiplicity of equilibria in the game of life creates an equilibrium selection problem for evolution to solve if she
is to get the players organized into a properly functioning society. In the Driving Game, for example, how is she to
replace the inefficient social contract in which drivers randomize by an efficient social contract in which everyone
drives on the same side of the road?
The folk theorem tells us that this problem of multiple equilibria was much worse in the repeated games played by our
prehuman ancestors. Not only are all the efficient outcomes on which rational players might like to agree available as
equilibrium outcomes, but so are large numbers of inefficient equilibria. Why should we expect evolution to succeed in
selecting one of the efficient equilibria rather than one of the many inefficient alternatives?
The answer postulates competition among groups. Suppose that many identical small societies are operating one of
two social contracts, a and b. If a makes each member of a society that operates it fitter than the corresponding
member of a society that operates b, then here is an argument which says that a will eventually come to predominate.
To say that a citizen is fitter in this context means that the citizen has a larger number of children on average. Societies
operating social contract a will therefore grow faster. Assuming societies cope with population growth by splitting off
colonies which inherit the social contract of the parent society, we will then eventually observe large numbers of copies
of societies operating social contract a compared with those operating contract b.
This retelling of the standard evolutionary story is unusual in two respects. The first is that selection takes place among
groups. So why isn't it an example of the group selection fallacy?
The reason is that a social contract is identified with an equilibrium of the game of life played by each of the competing
societies. But selection among equilibria doesn't require that individuals sacrifice anything for the public good, because
every individual in every group is already optimizing his or her fitness by acting in accordance with the social contract
of his society. The paradigm of the selfish gene is therefore maintained throughout.
The second unusual feature of the story is that the social contract of a parent society is transmitted to its colonies by
cultural rather than genetic means.
This observation confuses critics of sociobiology, because they have convinced themselves that sociobiologists are
"genetic determinists". An aside on the subject of coevolution is therefore necessary to press home the point that
sociobiologists don't subscribe to the patently silly view that everything which matters about human beings is
determined by their genes. Just like everyone else, they believe that culture matters.
Coevolution.
What distinguishes us from other animals? The naive answer is that evolution somehow endowed us with bigger
brains, which we use to create the
arts and sciences that allow us to dominate the world. However, I think the sociobiologists are much more likely to be
right when they deny the simplistic assumption that our big brains came first, and hence are entitled to a primary role
in explaining the success of our species.
Although their critics accuse them of believing that nothing but biology is relevant to human behavior, the mainstream
sociobiological position adopted in books like Laura Betzig's Human Nature or Boyd and Richerson's Culture and the
Evolutionary Process, is that we are a product of both biological and cultural evolution operating in tandem. Edward
Wilson went so far as to adopt the term coevolution to emphasize that what we learn from the culture in which we grow
to maturity is as important to us as the instincts written into our genes.
As the various wild boy stories suggest, our big brains are useless to us unless we grow up in a culture that provides
them with appropriate inputs at the correct development stage. Rather than simply substituting a big brain theory for
Descartes' divine spark, the lesson is that we need to treat culture as an autonomous phenomenon in its own right.
How does our culture separate us from other animals? After all, chimpanzees and baboons are also social, and hence
maintain a culture of sorts. Even songbirds learn what songs it is fashionable to sing by listening to their neighbors.
Apart from our peculiar sexual behavior, the obvious answer is that we have a highly flexible language, whereas other
animals are restricted to a limited menu of signals that relate only to events that are immediately at hand. But to
understand the origins of human social contracts, I think we need to go back to a time before human signalling systems
were recognizable as languages to ask what made human societies such a fertile ground for the growth of language. My
guess is that coevolution had by then already made the large step that separates us from other apes.
Our species somehow learned to use culture as a form of collective unconscious or group mind within which to store
the fruits of trial-and-error experimentation from the past, and to incorporate new discoveries made by individuals in
the present. Such a cultural resource allows a group to react flexibly in the face of new challenges or opportunities, and
hence creates a larger metaphorical cake for the group than would be possible if everybody only knew what they could
find out by themselves.
A great deal of our culture is concerned with how we get along with each other; how we split the cake we have jointly
created without wasteful conflict. It is this aspect of our social contract with which I am most concerned. Many
anthropologists still maintain that only our cultural heritage is relevant to such questions, but it seems obvious to me
that human biology must impose constraints on what social contracts can evolve, just as human biology imposes
constraints on the deep structure of the languages that can evolve.
David Hume was making a similar point when he observed that the "natural laws" that govern our societies are
actually artificial, but are called "natural" because everyone can see that it is natural to the human species that we
should have such laws. Similarly, it is natural that a human society should have a language, but its actual language is an
artifact of its cultural history. I think that the same is true of social contracts in general. It is natural that a human
society should have a social contract, but its actual social contract is an artifact of its cultural history.
If we want to look for universals in the morals of the human species, we therefore have to look beneath the differing
cultures of different societies. We must look at the deep structure of human social contracts written into our genes.
Traditionalists are virulently hostile to this suggestion, because they think that nothing is written in our genes but the
savagery of nature, red in tooth and claw. I think they are right to the extent that the only social contracts available to
us are equilibria in our game of life, but wrong in supposing that such equilibria must necessarily resemble Hobbes'
state of nature—in which life is "solitary, poor, nasty, brutish and short". On the contrary, the folk theorem tells us that
constraining our prehuman ancestors to social contracts that correspond to equilibria in their repeated game of life
would have been no bar at all to the evolution of efficient cooperation in their societies.
Stability tells us that social contracts need to be equilibria of the game of life. But most games have many equilibria,
and so we face an equilibrium selection problem. Efficiency takes us some way toward solving this problem, but the
folk theorem tells us that many efficient equilibria are available as possible social contracts. To operate successfully, a
society needs to single out one of these on which to coordinate.
For example, in the Tragedy of the Commons, the efficient number of goats is 1,000. These can be divided up among
the 100 families in many ways, each of which can be supported as an equilibrium outcome of the repeated version of
the game. Since we know nothing about the special circumstances of the families in the story, one of these outcomes
shrieks for special attention—that in which each family gets to keep 10 goats. Why? Because something tells us it is the
fair outcome.
Why do we care about fairness? I think we care because fairness is evolution's solution to the equilibrium selection
problem for our ancestral game of life.
What evidence is there for this conjecture? All the societies studied by anthropologists that survived into modern times
with a pure hunter-gathering economy had similar social contracts with a similar deep structure. This applies across the
world—to Kalahari bushmen, Greenland eskimos, Australian aborigines, and Brazilian indians. They tolerate no
bosses, and they share on a very egalitarian basis.
I will have more to say about this fascinating fact, but right now I want only to emphasize that although this global
behavior is presumably genetically determined, we are obviously not helpless victims of a genetic predisposition to live
in utopian anarchies in which each contributes according to his abilities and receives according to his need. As the
economic means of production of a society becomes more complex, its social contract must necessarily adapt if the
potential gains from improved technology and the division of labor are to be efficiently exploited. But all the many
adaptations that history records are almost certain to have a cultural origin, since the time spans are too short for a
biological explanation to be plausible.
Anthropologists started gathering quantitative evidence about food sharing only when pure hunter-gathering societies
were on their last legs. So we don't know how important culture was in determining precisely how much was thought
fair for different people in different societies. But if the general assessment of the way that fairness norms work in
modern societies offered in such books as Elster's Local Justice or Young's Equity is a reliable guide, then there is
currently a great deal of cross-cultural variation. So it can't be that the fairness norms we use are determined entirely by
our genes.
What counts as fair in different societies can vary as much the languages spoken. Just as different dialects may be used
in different regions of a basically monoglot country, so different views of what counts as fair may operate in different
societies, or in the same society at different places or times. Individuals of a particular society even operate different
standards when interacting with different groups, or with the same group in a different context—just as schoolkids
speak a teenage argot to each other, but communicate with their parents quite comprehensibly.
I have been arguing that what we count as fair depends both on our culture and on our genes. Since cultures vary, any
universal principles of justice—its deep structure—must presumably be written into the genes that we all share as
members of the same species. If I am right in guessing at the existence of such a deep structure, the next question asks
itself. What shape does the deep structure of fairness take?
The Original Position.
The thesis I defend in this book is that the common deep structure of human fairness norms is captured in a stylized
form by an idea that John Rawls called the device of the original position in his celebrated Theory of Justice.
Rawls uses the original position as a hypothetical standpoint from which to make judgments about how a just society
would be organized. Members of a society are asked to envisage the social contract to which they would agree if their
current roles were concealed from them behind a "veil of ignorance". Behind this veil of ignorance, the distribution of
advantage in the planned society would seem determined as though by a lottery. Devil take the hindmost then becomes
an unattractive principle for those bargaining in the original position, since you yourself might end up with the lottery
ticket that assigns you to the rear.
Rawls defends the device of the original position as an operationalization of Immanuel Kant's categorical imperative,
but I think this is just window-dressing. The idea certainly hits the spot with most people when they hear it for the first
time, but I don't believe this is because they have a natural bent for metaphysics. I think it is because they recognize a
principle that matches up with the fairness norms that they actually use every day in solving the equilibrium selection
problem in the myriads of small coordination games of which daily life largely consists.
It is important to emphasize that I am not following Rawls here in talking about the grand coordination problems
faced by a nation state. Our sense of fairness didn't evolve for use on such a grand scale. Nor am I talking about the
artificial and unrealistic principles of justice promoted by self-appointed moral pundits, to which people commonly
offer only lip service. Nor am I talking about the kind of moral pathology that led Osama bin Laden to believe that
thousands of innocent New Yorkers should die to compensate for the humiliations that he thought Islam
had received at the hands of the West. I am talking about the real principles that we actually use in solving everyday
coordination problems.
The sort of coordination problems I have in mind are those that we commonly solve without thought or
discussion—usually so smoothly and effortlessly that we don't even notice that there is a coordination problem to be
solved. Who goes through that door first? How long does Adam get to speak before it is Eve's turn? Who moves how
much in a narrow corridor when a fat lady burdened with shopping passes a teenage boy with a ring through his nose?
Who should take how much of a popular dish of which there isn't enough to go around? Who gives way to whom
when cars are maneuvering in heavy traffic? Who gets that parking space? Whose turn is it to wash the dishes tonight?
These are picayune problems, but if conflict arose every time they needed to be solved, our societies would fall apart.
Most people are surprised at the suggestion that there might be something problematic about how two people pass
each other in the corridor. When interacting with people from our own culture, we commonly solve such coordination
problems so effortlessly that we don't even think of them as problems. Our fairness program then runs well below the
level of consciousness, like our internal routines for driving cars or tying shoelaces. As with Molière's Monsieur
Jourdain, who was delighted to discover that he had been speaking prose all his life, we are moral in small-scale
situations without knowing that we are moral.
Just as we only take note of a thumb when it is sore, we tend to notice moral rules only when attempts are made to
apply them in situations for which they are ill-adapted. We are then in the same position as Konrad Lorenz when he
observed a totally inexperienced baby jackdaw go through all the motions of taking a bath when placed on a marbletopped table. By triggering such instinctive behavior under pathological circumstances, Lorenz learned a great deal
about what is instinctive and what is not when a bird takes a bath. But this vital information is gained only by avoiding
the mistake of supposing that bath-taking behavior confers some evolutionary advantage on birds placed on marbletopped tables.
Similarly, one can learn a lot about the mechanics of moral algorithms by triggering them under pathological
circumstances—but only if one doesn't make the mistake of supposing that the moral rules are adapted to the
coordination problems they fail to solve. However, it is precisely from such sore-thumb situations that I think
traditional moralists unconsciously distill their ethical principles. We discuss these and only these situations endlessly,
because our failure to coordinate successfully brings them forcefully to our attention.
This isn't to say that we shouldn't talk about such games. On the contrary, it is partly because we need to extend the
class of games that our social contract handles adequately that it is worth studying the problem at all. But we won't
learn how natural morality works by confining our attention to situations where it doesn't.
Egalitarian or Utilitarian?
In arguing that Rawls' original position is built into the deep structure of human fairness norms, I have two tasks. The
first task is to offer a plausible account of the evolutionary pressures that might have resulted in such a mechanism
being written into our genome. The second task is to explain
how this biological mechanism interacts with our cultural heritage to generate a specific choice of equilibrium in some
of the games of life we play.
The first task will have to sit on a back-burner until Chapter 9, but the second task needs more immediate attention,
because the orthodox literature on the original position points in two directions that are commonly thought to be
diametrically opposed. John Rawls argues that, after the basic rights and liberties of each citizen have been secured,
using the device of the original position will lead to an egalitarian distribution of goods and services. John
Harsanyi—who independently proposed the device of the original position around the same time as Rawls—argues
that its use will lead to a utilitarian distribution.3
My naturalistic approach reconciles Harsanyi's and Rawls' conclusions to some extent, but the reconciliation is
achieved at the expense of de-Kanting their ideas into a Humean bottle—an activity which both viewed with only
cautious sympathy. However, adopting such a new perspective not only allows us to dispense with all metaphysical
reasoning, it also allows us to relate the human capacity for empathy to our use of fairness as a coordinating device.
Empathy and Interpersonal Comparison.
The original position might be said to be a do-as-you-would-be-done-by principle that takes account of the objection
that you shouldn't do unto others as you would have them do unto you, because they may not have the same tastes as
yours. For example, Adam may be a keen jogger who likes to be woken before dawn for a ten-mile run through the ice
and snow, but Eve is unlikely to respond well if he shakes her awake before the sun has risen on the grounds that this
is what he would like her to do for him.
The original position forces Adam to take account of Eve's tastes in such situations by requiring him to consider how
it would be if he were to emerge from behind the hypothetical veil of ignorance occupying her role in life. He must
therefore have the capacity to empathize with her by putting himself in her position to see things from her point of
view. She must simultaneously be able to empathize with him by putting herself in his shoes to see things from his
point of view.
John Harsanyi saw that to get a grip on what it means for two rational people to empathize with each other is to solve
the long-standing puzzle of how interpersonal comparisons of utility can sensibly be made. He thereby created a
simple theory in which Adam and Eve's welfare can be measured in a way that makes fairness comparisons possible.
He sought to explain the standard of interpersonal comparison that arises in metaphysical terms, but I think that this
standard is an artifact of the cultural history of a society.
This claim that our standards of interpersonal comparison of utility are culturally determined is the second pillar of my
analogy between fairness and language. Elster's Local Justice and Young's Equity document how widely fairness norms
can differ in different times and places, but the implicit assumption in describing the differing norms is that the
standard of interpersonal comparison is unproblematic, and it is the basic structure of the norm that varies. My
alternative explanation for at least
Harsanyi attributes the idea to William Vickrey. The philosopher, Robert Hare, gives credit for his own version of the idea to C. I. Lewis.
some of the variation is that our biology guarantees that the deep structure is always the device of the original position,
leaving differences in the observed norms to be explained largely by cultural or contextual variations in the standards
of interpersonal comparison.
But how are we to incorporate such considerations into our analysis of how Adam and Eve will bargain in the original
position? What relevance do they have for the debate between Harsanyi and Rawls? Should we expect everyday
fairness norms to be egalitarian or utilitarian? Even a broad-brush account requires some knowledge of the economic
theory of bargaining, but before moving on to this task in the next chapter, I want to summarize where we have got to
The feature of my theory of fairness previewed in this chapter is the claim that all fairness norms in actual use share
the deep structure of Rawls' original position. This deep structure is biologically determined, and hence universal in the
human species, but the standards of interpersonal comparison that the original position needs as inputs are culturally
determined, and hence vary with time and place.
The analogy with language is close. Like language, I think that our capacity to resolve coordination problems using
fairness criteria is one of those few characteristics of our species that separates us from other animals. I know the
speculation is bold, but I hope I have made the idea seem plausible enough that it seems worth pursuing its
implications in the following chapters.
Karl Marx might respond that it is all very well seeking to understand society, but the point is to change it, and I don't
disagree. I hope very much that the scientific study of how societies really work will eventally make the world a better
place for our children's children to live in, by clarifying what kind of reforms are compatible with human nature, and
which are doomed to fail because they aren't.
As an example, consider the pragmatic suggestion that we might seek to adapt the fairness norms that we use on a
daily basis for settling small-scale coordinating problems to large-scale problems of social reform. This is one of the
few things I have to say that traditional moralists find halfway acceptable. But they want to run with this idea without
first thinking hard about the realities of the way that fairness norms are actually used in solving small-scale problems.
In particular, they are unwilling to face up to the fact that fairness norms didn't evolve as a substitute for the exercise
of power, but as a means of coordinating on one of the many ways of balancing power.
This refusal to engage with reality becomes manifest when traditionalists start telling everybody how they "ought" to
make interpersonal comparisons when employing the device of the original position. But if I am right that the
standards of interpersonal comparison we actually use as inputs when making small-scale fairness judgments are
culturally determined, then these attitudes will necessarily reflect the underlying power structure of a society. One
might wish, for whatever reason, that these attitudes were different. But the peddling of metaphysical arguments about
what would be regarded as fair in some invented ideal world can only muddy the
waters for practical reformers who actually have some hope of reaching peoples' hearts. Nobody is going to consent to
a reform on fairness grounds if the resulting distribution of costs and benefits seems to them unfair according to
established habit and custom, whatever may be preached from the pulpit.
It is true that facing up to such facts requires recognizing that it is sometimes pointless or counter-productive to urge
reforms for which a society isn't ready. What would anyone have gained by urging the abolition of slavery in classical
times, when even Aristotle thought that barbarians were natural slaves? What of the emancipation of women at a time
when even the saintly Spinoza took time out to expound on their natural inferiority? Instead of tilting at such
windmills, I think reformers need to make a hard-nosed assessment of the nature of the current social contract, and all
the possible social contracts into which it might conceivably be transformed by pushing on whatever levers of power
are currently available. Only when one has seriously thought through this feasibility question is there any point in
asking what is optimal.
This pragmatic attitude mystifies traditional moralists, who pretend not to understand how a naturalist like myself can
talk about optimality at all. How do I know what is best for society? What is my source of authority? Where are my
equivalents of the burning bush and the tablets of stone?
The answer is that I have no source of moral authority at all—but I think everyone else is in precisely the same boat. I
know perfectly well that my aspirations for what seems a better society are just accidents of my personal history and
that of the culture in which I grew up. If my life had gone differently or if I had been brought up in another culture, I
would have had different aspirations. But I nevertheless have the aspirations that I have—and so does everyone else.
The only difference between naturalists and traditionalists on this score is that naturalists don't try to force their
aspirations on others by appealing to some invented source of absolute authority. We don't need a source of authority
to wish that society were organized differently. If there are enough people with similar aspirations sufficiently close to
the levers of power, they can get together and shift the social contract just because that is what they want to do—and
for no other reason.
We naturalists think that this is what always happens anyway when reforms are consciously implemented, whatever the
accompanying rhetoric may be. We would doubtless be more successful in recruiting others to our way of thinking if
we too followed the traditional line of looking around for whatever line of rhetoric is currently most persuasive, but
intellectual honesty is one of the artificial virtues that cultural history has somehow lodged in our heads.
How and why we got stuck with this inconvenient meme is a mystery that I am at a loss to explain, but we bear up
under the handicap as best we can by making fun of the castles in the air built by our opponents. However, my attempt
to join in the fun will have to wait until chapter 3, since the next item on the agenda is a whirlwind tour of bargaining
Chapter 2 Bargaining
When I suggested twenty-five, a nicer-looking number than his thirty, he shook his grey head regretfully, and so we
went on haggling, and he haggled better than me, so that eventually we settled on thirty-five.
P. G. Wodehouse, Aunts Aren't Gentlemen
This chapter continues the broad-brush survey of my theory of fairness begun in chapter 1 by looking at the
bargaining questions that arise when discussing the original position.
When two people use fairness to resolve an everyday coordination problem, I believe they are implicitly calculating the
agreement that they would reach if they were to bargain on the assumption that their identities would be reassigned at
random after the negotiation was over. Although such hypothetical bargaining usually operates beneath our level of
consciousness, we are sufficiently aware of what is going on that most of us feel a thrill of recognition when the
mechanism is described to us for the first time in terms of John Rawls' original position.
I would like to see the original position used as Rawls envisaged to focus the reforming zeal of those among us who
think our children's children would lead more satisfying lives in a fairer society. But I differ from most people with
similar aspirations in believing that its potential for solving social problems will evaporate if we fail to use it for largescale purposes in the same way that we currently use it when settling picayune fairness questions.
It is particularly important to be realistic about the bargaining we imagine taking place behind the veil of ignorance. If
the hypothesized bargaining were outside the experience of the players using the device of the original position, how
could they be using it at present—albeit only for such petty matters as deciding who should wash the dishes tonight?
Progress therefore depends on having access to a sound economic theory of bargaining. Not only must such a theory
be realistic about the rules it postulates
to govern how the bargainers negotiate, it must also put aside the temptation to attribute motives to bargainers in the
original position beyond the urge to advance their own self-interest. Fairness criteria therefore have no place in the
theory to be used in predicting how people would bargain in the original position. Aside from other considerations,
there wouldn't be any point in proposing the original position as a final court of appeal on fairness questions if it
couldn't itself be used without making fairness judgments. Nor would the use of nonstrategic bargaining fit the
evolutionary origins for the original position that I shall be proposing in chapter 9.
This isn't to say that theories of fair bargaining are meaningless or devoid of interest. On the contrary, one of the
objectives of this book is to defend a particular view of what constitutes a fair bargain. But such a view should emerge
as one of the outputs of the theory rather than being subsumed among its inputs.
Thomas Schelling conducted some instructive experiments in the fifties on how people manage to solve coordination
problems. In his best known experiment, the subjects were asked what two people should do if they had agreed to
meet up in New York tomorrow without specifying a place and time in advance. The standard answer was that they
should go to Grand Central Station at noon. In London, it would have been Piccadilly Circus.
When people commonly agree on how to resolve such coordination problems, Schelling says that the consensus they
report constitutes a focal point. I think it significant that people seem to have little advance insight into what will turn
out to be relevant in determining what counts as focal, but that they are neverthless rather good at recognizing what
other people will regard as focal in any particular coordination problem. This book is about the kind of focal points
that people call fair. Fairness doesn't arise in Schelling's New York example because the protagonists don't care where
they meet up as long as they meet up somewhere. However, in the Meeting Game that I plan to use as a numerical
example when discussing bargaining issues, Adam and Eve have opposing views on where it would be best to meet.4
Table 1:Adam and Eve's Payoffs at Each Location in the Meeting Game.
Adam's 0
Eve's
Each player independently chooses one of the locations in Table 1 at which to
A politically incorrect version of the Meeting Game is traditionally called the Battle of the Sexes. Adam and Eve are a pair of honeymooners who failed to agree on whether to
meet up at the ballet or a boxing match. Eve prefers the former and Adam the latter.
await the other. If they choose the same location, each receives the corresponding payoff, measured in the notional
units of utility that economists call utils. If they choose different locations, Adam gets a small payoff of 4, and Eve a
small payoff of 2. They therefore have a common interest on coordinating on the same location, but Adam prefers
locations to the right, and Eve prefers locations to the left.
How should Adam and Eve resolve this archetypal coordination problem? Two locations can be ruled out
immediately. Adam would rather not meet at all than meet at location 1. Eve would rather not meet at all than meet at
location 10. However, each of the other eight locations is an efficient equilibrium of the Meeting Game, and so Adam
and Eve are faced with the kind of equilibrium selection problem that I believe fairness evolved to solve.
How does fairness work in such situations? Numerous theories compete for attention, but the two leading contenders
are the egalitarian and the utilitarian concepts of a fair outcome. I believe the literature is right to focus on these two
alternatives, but which applies in what circumstances? I think we can decide this question in any particular case by
appealing to the device of the original position. However, to predict the deal that Adam and Eve would reach if they
were to bargain behind the veil of ignorance, we need a realistic theory of strategic bargaining.
What would be the result of applying such a theory of strategic bargaining directly in the Meeting Game? That is to say,
if Adam and Eve were selfish players offered the opportunity to bargain face-to-face, on which location would it be
rational for them to agree? The rest of this chapter compares the answer that game theory offers to this question with
the result of applying various egalitarian and utilitarian fairness norms to the same problem.
Figure 1 shows a general bargaining problem stripped down to its essentials. The shaded set X represents the set of all
feasible agreements. The two coordinates of a point in X represent the payoffs that the two players will receive if they
agree on this point. As in the Meeting Game, these payoffs are measured in notional units of utility called utils. The
boundary of the feasible set X consists of all the efficient agreements that are available.
The point within the feasible set marked with the letter D represents the status quo—the outcome that will result if
Adam and Eve fail to reach an agreement at all. The thickened part of the boundary shows all the efficient agreements
that both players agree are at least as good as the disagreement point D. It is generally accepted that rational players will
agree on one of these points, but we shall need to say more than this.5
If the disagreement point D is placed at the point (4, 2), a bargaining problem can be regarded as a generalization of
the Meeting Game in which inefficient points of the feasible set X are available as agreements as well as the efficient
points on
Economists refer to the claim that rational players will agree on an efficient outcome as the Coase theorem, although Edgeworth made the same proposal as far back as 1881.
the boundary of X that correspond to locations in the Meeting Game.
Figure 1: A bargaining problem that generalizes the Meeting Game, whose ten locations have been numbered. To find
the Nash bargaining solution N, draw the tangent that touches the boundary of X halfway between A and B.
Social Contracts.
In this book, social contract questions are nearly always simplified by restricting attention to just two players, whom I
romantically envisage as Adam and Eve after their expulsion from the Garden of Eden.
When offering a social contract interpretation of a bargaining problem, each point in the feasible set X is identified
with the pair of utilities or payoffs that Adam and Eve will receive if they coordinate on one of the many equilibria in
the repeated game of life that they must now face. The set X represents the set of all their feasible social contracts—all
the stable forms of social and economic organization that are possible within the human game of life. The
disagreement point D in a bargaining problem represents the inefficient social contract that Adam and Eve are
assumed to be operating at present.
It is easy to lose sight of how much significant social activity is being packed away in a black box when all that is
retained of the rich structure of a social contract is a pair of payoffs in the set X. In particular, the stability issues that
commonly monopolize the attention of right-wing thinkers are abstracted away almost entirely—but they are not
therefore to be forgotten.
Nobody denies that the wealth of a society depends on the freedom it offers to
its entrepreneurs and the incentives it offers to its workers, but such considerations are built into the structure of an
equilibrium in the game of life. We need to take them into account when determining what payoffs to assign each
equilibrium when constructing the set X. In particular, social contracts that make proper use of markets will tend to
generate higher payoffs than command economies. However, after the set X has been constructed, such issues will be
visible only to the extent that they determine the size and shape of X.
Of course, after a social contract has been chosen from the feasible set X, it is necessary to unpack the black box so
that everyone can be told what strategy they need to play in order that society can implement the agreed outcome. All
the issues that right-wing thinkers suspect are being neglected when we are discussing what efficient outcome it would
be fair to choose from X then come to the fore.
The State of Nature.
When talking about social contracts, it is traditional to refer to the disagreement point as the state of nature, but my state
of nature doesn't at all resemble Thomas Hobbes' "war of all against all". Nor is it related to John Locke's pastoral
idyll, in which everybody enjoys natural rights, according to which: "No one ought to harm another in his life, health,
liberty or possessions", and property rights are acquired by mixing one's labor with a good, provided that there be
"enough and as good left in common for others". These seem to me to be mere fictions, invented to generate
conclusions that favor a particular prejudice.6
Nor do I see much point in following the utilitarians in pretending that a new Jerusalem can be established without
paying any attention to the current social contract at all. You may recall the old Irish joke of the peasant who explained
that if he were going to Dublin, he wouldn't start from here. He is right that we would perhaps do better if we were
able to start from somewhere else, or from nowhere at all. But here is where we are at. Like it or not, we are what
history has made of us.
How are bargaining problems solved when two parties negotiate face-to-face, bringing to bear whatever bargaining
power they may have at their disposal? In such strategic bargaining, fairness has only a rhetorical function. For
example, Jon Elster counted 24 different fairness norms proposed in Swedish wage negotiations. Instead of crude
demands for this hourly rate or that, the bargainers could then discuss whose "fairness norm" would apply!
Game theory has made substantial advances in analyzing strategic bargaining among rational players when the
characteristics of the players and the nature of the bargaining problem are common knowledge. I therefore always stick
with this case, although it is sometimes less than realistic. The reason is that a number of different lines of enquiry then
converge on identifying the Nash bargaining solution as the
Hobbes was seeking to legitimize the monarchy after the chaos of the English Civil War. Locke was similarly conjuring up an argument that would legitimize the morality of
the new commercial classes that was replacing the medieval Christian tradition in his time.
rational agreement when the players have equal bargaining power.7
The Nash who first proposed the Nash bargaining solution is the same as the Nash who formulated the concept of a
Nash equilibrium, but it will be obvious that the two ideas are very different. There are few takers for this point of
view, but I think Nash deserves his Nobel prize more for his bargaining solution than for his equilibrium concept,
since his contribution to bargaining theory is entirely original, whereas his equilibrium idea had a number of
precursors.
Locating the Nash bargaining solution in numerical examples is simple. It occurs where the product of the players'
gains over their disagreement payoffs is largest. The Nash bargaining solution in the Meeting Game is therefore
location 7, because the product of gains there is (34 − 4) × (22 − 2) = 600, which exceeds the product of gains at any
other location.8 Its nearest rivals are locations 6 and 8, where the product of gains are (28 − 4) × (26 − 2) = 576 and
(40 − 4) × (18 − 2) = 576.
Geometrically minded folk may prefer to note that the Nash bargaining solution lies at the point marked with the letter
N in figure 1. This point is halfway between the points A and B on the tangent to the boundary of X at N.
Why the Nash Bargaining Solution?
The Nash bargaining solution is game theory's best shot at predicting the agreement that will be reached when two
rational players with equal bargaining power negotiate face-to-face without any appeals to fairness being made. It has
rivals, like the version of the Kalai-Smorodinsky bargaining solution reinvented by David Gauthier in his Morals by
Agreement, but none of these rivals allow the same defense in depth as the Nash bargaining solution. However, this isn't
a book on strategic bargaining, and so I only give the most naive of the arguments that can be offered in its support.
The point N is halfway between A and B in figure 1. If the bargainers have equal bargaining power, N is therefore the
natural candidate for the outcome of a rational negotiation when the feasible set is everything under the straight line
through A and B. Now throw away outcomes from this notional feasible set until we get the feasible set with which we
started. These discarded alternatives are "irrelevant", since the bargainers chose to reject them in favor of N when they
were available. The agreed outcome should therefore continue to be N after they are thrown away, because "nothing
that matters" in the negotiation has changed.
Nash supplemented this argument by looking at a specific bargaining model in which the two players make
simultaneous take-it-or-leave-it demands (Section 4.7). Such bargaining games always have many equilibria, but a
natural resolution of the equilibrium selection problem yields the Nash bargaining solution. Ariel Rubinstein studied
the more realistic case in which the players alternate in making demands until someone gives in. A natural resolution of
the equilibrium selection problem again yields the Nash bargaining solution, provided that the time interval between
I focus on the case of equal bargaining power because the available bargaining strategies behind the veil of ignorance are the same for both players.
It remains largest if we allow Adam and Eve to toss a coin or cut cards to settle any disputes, but I don't plan to worry much about the use of random devices as instruments
of compromise in this chapter.
successive demands is sufficiently small.
These and other arguments supporting the Nash bargaining solution are strong but not entirely overwhelming. What
would happen if some sensible alternative were substituted for the Nash bargaining solution in my theory? The details
of the theory would then become more complicated, but I think it unlikely that there would be substantive qualitative
changes in the conclusions.
Why not Bargain Directly?
The Nash bargaining solution has been introduced to help predict the outcome of bargaining in the original position.
But why not use it to solve Adam and Eve's bargaining problem directly? There are two reasons.
The first reason is that fairness evolved for use in situations in which face-to-face bargaining isn't an alternative option.
My guess is that it probably predates language. After all, we had to have some way of coordinating with each other to
create the conditions under which true language could evolve. Nowadays, we mostly use fairness norms in everyday
situations in which it is either impossible to negotiate, or in which the benefits of negotiating are outweighed by the
costs in time or money.
The second reason is that the Nash bargaining solution has no fairness content whatsoever. This becomes obvious
when one notes that the outcome it generates doesn't depend at all on the scales we use to measure Adam and Eve's
utilities. For example, if we double Adam's utils so that each new util is worth half an old util, the new Nash bargaining
solution simply doubles the number of utils that Adam gets. Thus, in the Meeting Game, the Nash bargaining solution
selects location 7 both before and after we double all of Adam's payoffs (including his disagreement payoff). It
similarly selects location 7 both before and after we add 3 to all of Eve's payoffs. How could matters be otherwise in
strategic bargaining? Players can't alter their bargaining power by changing the scale they choose to measure their
utility, any more than a physicist can change how warm a room is by switching from degrees Celsius to degrees
Fahrenheit.
The Nash bargaining solution doesn't even begin to qualify as a fairness norm, because a minimal requirement for a
fairness criterion is that it somehow compares Adam and Eve's welfare.
Economics textbooks commonly say that such interpersonal comparisons of utility are impossible. Taken literally, this
is just a piece of dogma without any theoretical justification, but the textbooks are right to the extent that one can't just
assume that Adam's utils can be traded against Eve's at some commonly understood rate, in the manner almost
universal among those philosophers who address the issue at all. I therefore think it important to register that I follow
John Harsanyi in basing a theory of interpersonal comparison of utility on the ability of human beings to empathize
with each other.
Empathetic Identication.
If Adam and Eve are autistic or unable to empathize successfully with each other for other reasons, then the device of
the original position won't work for them. When our attempts to use fairness norms in everyday games go awry, as
they do every now and then, I think it is largely because of such failures in empathetic identification. But, in attempting
to make a first stab at explaining how fairness norms work, I follow Harsanyi in looking at the idealized case in which
Adam is totally successful in his attempts at empathizing with Eve.
It may be that Adam is modest, and so would prefer a fig leaf to an apple if forced to choose between them. But if Eve
is a brazen hussy who would choose the apple in the same situation, then our idealized Adam will accept that if he were
Eve, then he would take the apple too. With this assumption, Harsanyi gave a simple argument which implies that
people in the original position will bargain as though they think that Adam's utils can be traded against Eve's utils at
some fixed rate.
I don't suppose anyone but the most diehard of neoclassical economists denies that we actually do have standards for
making interpersonal comparisons of utility, and that these are widely shared within a particular society. However,
people don't commonly ask why evolution should have equipped our brains with the unconscious capacity to make the
complicated calculations necessary to determine who is worth how much in this or that situation.
It is easy to guess that the origins of the capacity lie in the need for members of an extended family to recognize how
closely they are related to each other. But why do we need to make interpersonal comparisons of utility outside the
family? One reason is that such comparisons are necessary as inputs to the device of the original position. It is a strong
claim, but I think this is the only reason that evolution provided us with the capacity to compare our welfare with the
rest of humankind.
But why should everyone in a particular context employ the same standard of interpersonal comparison, as Harsanyi
and Rawls assume? I think that we must look at the cultural history of a society for the answer. That is to say, the
standards of interpersonal comparison that are current in a society are determined by social or cultural evolution, with
the result that any differences in the standards being operated tend to be ironed out in the long run (chapter 8).
As noted in the previous chapter, the second pillar of my analogy between fairness and language is therefore the claim
that standards of interpersonal comparison of utility are culturally determined. This is why what counts as fair differs in
different places or times or contexts. Just as Japanese is different from French, so the fairness norms of modern New
York operate differently from those of classical Athens. For example, women count for a great deal more in the New
York of today than they did in Athens, but suckers no longer get an even break.
When making fairness judgments using the device of the original position, Adam and Eve don't actually negotiate at
all. They coordinate on the deal on which they would agree if they were to bargain behind the veil of ignorance. But what
would this deal
be? Harsanyi and Rawls independently asked this question, but came up with very different answers. Harsanyi argues
that the final outcome will be utilitarian. Rawls argues that it will be egalitarian.
For the utilitarian and the egalitarian bargaining solutions to be meaningful, we need to be given a social index for each
player. I hope this term is sufficiently neutral that it won't trigger any preconceptions about whether having a high or a
low social index is necessarily 'good' or 'bad'. Just as you like the price to be small when you are buying and large when
you are selling, so the significance of a high or a low social index depends crucially on the context.
We need social indices because nothing says that the personal payoffs used in specifying a bargaining problem can be
compared directly in a way that is meaningful for a fairness calculation. For example, if the payoffs in the Meeting
Game were given in dollars, nobody would want to say that Adam is better off than Eve at location 10 after learning
that he is a billionaire and she is a beggar.
We therefore rescale each player's personal payoffs by dividing them by the player's social index. The result of this
rescaling or weighting can be thought of as society's assessment of the worth of each possible outcome of the bargaining
problem to the player in question. More precisely, to say that Adam's social index is three and Eve's is two is to
proceed as though three of Adam's personal utils are worth the same as two of Eve's.
Such a social judgment will reflect a kaleidoscope of factors determined by the historical context in which a
coordination game like the Meeting Game has been played in