PART ONE
COMMON
SENSE
CHAPTER 1
The Myth of Common Sense
Every day in New York City five million people ride the subways. Starting from their homes throughout the boroughs of Manhattan, Brooklyn, Queens, and the Bronx, they pour themselves in through hundreds of stations, pack themselves into thousands of cars that barrel though the dark labyrinth of the Metropolitan Transportation Authorityâs tunnel system, and then once again flood the platforms and stairwellsâa subterranean river of humanity urgently seeking the nearest exit and the open air beyond. As anyone who has ever participated in this daily ritual can attest, the New York subway system is something between a miracle and nightmare, a Rube Goldberg contraption of machines, concrete, and people that in spite of innumerable breakdowns, inexplicable delays, and indecipherable public announcements, more or less gets everyone where theyâre going, but not without exacting a certain amount of wear and tear on their psyche. Rush hour in particular verges on a citywide mosh pitâof tired workers, frazzled mothers, and shouting, shoving teenagers, all scrabbling over finite increments of space, time, and oxygen. Itâs not the kind of place you go in search of the milk of human kindness. Itâs not the kind of place where youâd expect a perfectly healthy, physically able young man to walk up to you and ask you for your seat.
And yet thatâs precisely what happened one day in the early 1970s when a group of psychology students went out into the subway system on the suggestion of their teacher, the social psychologist Stanley Milgram. Milgram was already famous for his controversial âobedienceâ studies, conducted some years earlier at Yale, in which he had shown that ordinary people brought into a lab would apply what they thought were deadly electrical shocks to a human subject (really an actor who was pretending to be shocked) simply because they were told to do so by a white-coated researcher who claimed to be running an experiment on learning. The finding that otherwise respectable citizens could, under relatively unexceptional circumstances, perform what seemed like morally incomprehensible acts was deeply disturbing to many peopleâand the phrase âobedience to authorityâ has carried a negative connotation ever since.1
What people appreciated less, however, is that following the instructions of authority figures is, as a general rule, indispensible to the proper functioning of society. Imagine if students argued with their teachers, workers challenged their bosses, and drivers ignored traffic cops anytime they asked them to do something they didnât like. The world would descend into chaos in about five minutes. Clearly there are moments when itâs appropriate to resist authority, and most people would agree that the situation Milgram created in the lab would qualify as such a moment. But what the experiment also illustrated was that the social order that we take for granted in everyday life is maintained in part by hidden rules that we donât even realize exist until we try to break them.
Based on this experience, and having subsequently moved to New York, Milgram had begun to wonder if there was a similar âruleâ about asking people for seats on the subway. Like the rule about obeying authority figures, this rule is never really articulated, nor would a typical rider be likely to mention it if asked to describe the rules of subway riding. And yet it exists, as Milgramâs students quickly discovered when they went about their little field experiment. Although more than half of the riders asked eventually surrendered their seats, many of them reacted angrily or demanded some explanation for the request. Everyone reacted with surprise, even amazement, and onlookers often made disparaging remarks. But more interesting than the response of the riders was that of the experimenters themselves, who found it extremely difficult to perform the experiment in the first place. Their reluctance was so great, in fact, that they had to go out in pairs, with one of them acting as moral support for the other. When the students reported their discomfort to Milgram, he scoffed at them. But when he tried to do the experiment himself, the simple act of walking up to a complete stranger and asking for his or her seat left him feeling physically nauseated. As trivial as it seemed, in other words, this rule was no more easily violated than the obedience-to-authority âruleâ that Milgram had exposed years earlier.2
As it turns out, a big city like New York is full of these sorts of rules. On a crowded train, for example, itâs no big deal if youâre squeezed in against other people. But if someone stands right next to you when the train is empty, itâs actually kind of repellant. Whether itâs acknowledged or not, thereâs clearly some rule that encourages us to spread out as much as we can in the available space, and violations of the rule can generate extreme discomfort. In the same way, imagine how uncomfortable youâd feel if someone got on your elevator and stood facing you instead of turning around to face the door. People face each other all the time in enclosed spaces, including on subway trains, and nobody thinks twice about it. But on an elevator it would feel completely weird, just as if the other person had violated some ruleâeven though it might not have occurred to you until that moment that any such rule existed. Or how about all the rules we follow for passing one another on the sidewalk, holding open doors, getting in line at the deli, acknowledging someone elseâs right to a cab, making just the right amount of eye contact with drivers as you cross the street at a busy intersection, and generally being considerate of our fellow human beings while still asserting our own right to take up a certain amount of space and time?
No matter where we live, our lives are guided and shaped by unwritten rulesâso many of them, in fact, that we couldnât write them all down if we tried. Nevertheless, we expect reasonable people to know them all. Complicating matters, we also expect reasonable people to know which of the many rules that have been written down are OK to ignore. When I graduated from high school, for example, I joined the Navy and spent the next four years completing my officer training at the Australian Defence Force Academy. The academy back then was an intense place, replete with barking drill instructors, predawn push-ups, running around in the pouring rain with rifles, and of course lots and lots of rules. At first this new life seemed bizarrely complicated and confusing. However, we quickly learned that although some of the rules were important, to be ignored at your peril, many were enforced with something like a wink and a nod. Not that the punishments couldnât be severe. You could easily get sentenced to seven days of marching around a parade ground for some minor infraction like being late to a meeting or having a wrinkled bedcover. But what you were supposed to understand (although of course you werenât supposed to admit that you understood it) was that life at the academy was more like a game than real life. Sometimes you won, and sometimes you lost, and that was when you ended up on the drill square; but whatever happened, you werenât supposed to take it personally. And sure enough, after about six months of acclimation, situations that would have terrified us on our arrival seemed entirely naturalâit was now the rest of the world that seemed odd.
Weâve all had experiences like this. Maybe not quite as extreme as a military academyâwhich, twenty years later, sometimes strikes me as having happened in another life. But whether itâs learning to fit in at a new school, or learning the ropes in a new job, or learning to live in a foreign country, weâve all had to learn to negotiate new environments that at first seem strange and intimidating and filled with rules that we donât understand but eventually become familiar. Very often the formal rulesâthe ones that are written downâare less important than the informal rules, which just like the rule about subway seats may not even be articulated until we break them. Conversely, rules that we do know about may not be enforced, or may be enforced only sometimes depending on some other rule that we donât know about. When you think about how complex these games of life can be, it seems kind of amazing that weâre capable of playing them at all. Yet in the way that young children learn a new language seemingly by osmosis, we learn to navigate even the most novel social environments more or less without even knowing that weâre doing it.
COMMON SENSE
The miraculous piece of human intelligence that enables us to solve these problems is what we call common sense. Common sense is so ordinary that we tend to notice it only when itâs missing, but it is absolutely essential to functioning in everyday life. Common sense is how we know what to wear when we go to work in the morning, how to behave on the street or the subway, and how to maintain harmonious relationships with our friends and coworkers. It tells us when to obey the rules, when to quietly ignore them, and when to stand up and challenge the rules themselves. It is the essence of social intelligence, and is also deeply embedded in our legal system, in political philosophy, and in professional training.
For something we refer to so often, however, common sense is surprisingly hard to pin down.3 Roughly speaking, it is the loosely organized set of facts, observations, experiences, insights, and pieces of received wisdom that each of us accumulates over a lifetime, in the course of encountering, dealing with, and learning from, everyday situations. Beyond that, however, it tends to resist easy classification. Some common-sense knowledge is very general in natureâwhat the American anthropologist Clifford Geertz called an âancient tangle of received practices, accepted beliefs, habitual judgments, and untaught emotions.â4 But common sense can also refer to more specialized knowledge, as with the everyday working knowledge of a professional, such as a doctor, a lawyer, or an engineer, that develops over years of training and experience. In his address to the annual meeting of the American Sociological Society in Chicago in 1946, Carl Taylor, then president of the association, put it as well as anyone:
By common sense I mean the knowledge possessed by those who live in the midst and are a part of the social situations and processes which sociologists seek to understand. The term thus used may be synonymous with folk knowledge, or it may be the knowledge possessed by engineers, by the practical politicians, by those who gather and publish news, or by others who handle or work with and must interpret and predict the behavior or persons and groups.5
Taylorâs definition highlights two defining features of common sense that seem to differentiate it from other kinds of human knowledge, like science or mathematics. The first of these features is that unlike formal systems of knowledge, which are fundamentally theoretical, common sense is overwhelmingly practical, meaning that it is more concerned with providing answers to questions than in worrying about how it came by the answers. From the perspective of common sense, it is good enough to know that something is true, or that it is the way of things. One does not need to know why in order to benefit from the knowledge, and arguably one is better off not worrying about it too much. In contrast with theoretical knowledge, in other words, common sense does not reflect on the world, but instead attempts to deal with it simply âas it is.â6
The second feature that differentiates common sense from formal knowledge is that while the power of formal systems resides in their ability to organize their specific findings into logical categories described by general principles, the power of common sense lies in its ability to deal with every concrete situation on its own terms. For example, it is a matter of common sense that what we wear or do or say in front of our boss will be different from how we behave in front of our friends, our parents, our parentsâ friends, or our friendsâ parents. But whereas a formal system of knowledge would try to derive the appropriate behavior in all these situations from a single, more general âlaw,â common sense just âknowsâ what the appropriate thing to do is in any particular situation, without knowing how it knows it.7 It is largely for this reason, in fact, that commonsense knowledge has proven so hard to replicate in computersâbecause, in contrast with theoretical knowledge, it requires a relatively large number of rules to deal with even a small number of special cases. Letâs say, for example, that you wanted to program a robot to navigate the subway. It seems like a relatively simple task. But as you would quickly discover, even a single component of this task such as the âruleâ against asking for another personâs subway seat turns out to depend on a complex variety of other rulesâabout seating arrangements on subways in particular, about polite behavior in public in general, about life in crowded cities, and about general-purpose norms of courteousness, sharing, fairness, and ownershipâthat at first glance seem to have little to do with the rule in question.
Attempts to formalize commonsense knowledge have all encountered versions of this problemâthat in order to teach a robot to imitate even a limited range of human behavior, you would have to, in a sense, teach it everything about the world. Short of that, the endless subtle distinctions between the things that matter, the things that are supposed to matter but donât, and the things that may or may not matter depending on other things, would always eventually trip up even the most sophisticated robot. As soon as it encountered a situation that was slightly different from those you had programmed it to handle, it would have no idea how to behave. It would stick out like a sore thumb. It would always be screwing up.8
People who lack common sense are a bit like the hapless robot in that they never seem to understand what it is that they should be paying attention to, and they never seem to understand what it is that they donât understand. And for exactly the same reason that programming robots is hard, itâs surprisingly hard to explain to someone lacking in common sense what it is that theyâre doing wrong. You can take them back through various examples of when they said or did the wrong thing, and perhaps theyâll be able to avoid making exactly those errors again. But as soon as anything is different, theyâre effectively back to square one. We had a few cadets like that at the academy: otherwise perfectly intelligent, competent people who just couldnât seem to figure out how to play the game. Everyone knew who they were, and everyone could see that they just didnât get it. But because it wasnât exactly clear what it was that they didnât get, we were unable to help them. Bewildered and overwhelmed, most of them eventually left.
NOT COMMON AT ALL
As remarkable as it is, common sense exhibits some mysterious quirks, one of the most striking of which is how much it varies over time, and across cultures. Several years ago, for example, an enterprising group of economists and anthropologists set out to test how different cultures play a particular kind of game, called an ultimatum game. The game goes something like this: First, pick two people and give one of them $100. That person then has to propose a split of the money between himself and the other player, ranging from offering them the whole amount to nothing at all. The other player then gets to accept the deal or reject it. If the second player accepts the deal, they get what they were offered and both players go on their merry way. But if they reject the offer, neither player gets anything; hence the âultimatum.â
In hundreds of these experiments conducted in industrialized societies, researchers had already demonstrated that most players propose a fifty-fifty split, and offers of less than $30 are typically rejected. Economists find this behavior surprising because it conflicts with their standard notion of economic rationality. Even a single dollar, the reasoning goes, is better than nothing at all, so from a strictly rational perspective, recipients ought to accept any offer above zero. And knowing this, rational âproposersâ ought to offer the least they can get away withânamely, one dollar. Of course, a momentâs thought quickly suggests why people play the way they doânamely that it doesnât seem fair to exploit a situation just because you can. Recipients being offered less than a third therefore feel taken advantage of and so opt to walk away from even a substantial sum of money in order to teach miserly proposers a lesson. And anticipating this response, proposers tend to offer what they assume the recipient will consider a fair split.
If your reaction to this breakthrough insight is that economists need to get out a little more, then youâre not alone. If anything seems like common sense, itâs that people care about fairness as well as moneyâsometimes even more so. But when the experimenters replicated the game in fifteen small-scale preindustrial societies across five continents, they found that people in different societies have very different ideas about what counts as fair. At one extreme, the Machiguenga tribe of Peru tended to offer only about a quarter of the total amount, and virtually no offers were refused. At the other extreme, the Au and Gnau tribes of Papua New Guinea tended to make offers that were even better than fifty-fifty, but surprisingly these âhyperfairâ offers tended to get rejected just as frequently as unfair offers.9
What explains these differences? As it turns out, the Au and Gnau tribes had long-established customs of gift exchange, according to which receiving a gift obligates the receiver to reciprocate at some point in the future. Because there was no equivalent of the ultimatum game in the Au or Gnau societies, they simply âmappedâ the unfamiliar interaction onto the most similar social exchange they could think ofâwhich happene...