Everything Is Obvious (3 page)

Taylor’s 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 “as it is.”
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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 parents’ friends, or our friends’ parents. But whereas a formal system of knowledge would try to derive the appropriate behavior in all these situations from a single, more general “law,” common sense just “knows”
what the appropriate thing to do is in any particular situation, without knowing how it knows it.
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It is largely for this reason, in fact, that commonsense knowledge has proven so hard to replicate in computers—because, in contrast with theoretical knowledge, it requires a relatively large number of rules to deal with even a small number of special cases. Let’s 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 “rule” against asking for another person’s subway seat turns out to depend on a complex variety of other rules—about 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 ownership—that 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 problem—that 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 don’t, 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.
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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 don’t understand. And for
exactly the same reason that programming robots is hard, it’s surprisingly hard to explain to someone lacking in common sense what it is that they’re doing wrong. You can take them back through various examples of when they said or did the wrong thing, and perhaps they’ll be able to avoid making exactly those errors again. But as soon as anything is different, they’re effectively back to square one. We had a few cadets like that at the academy: otherwise perfectly intelligent, competent people who just couldn’t seem to figure out how to play the game. Everyone knew who they were, and everyone could see that they just didn’t get it. But because it wasn’t exactly clear what it was that they didn’t get, we were unable to help them. Bewildered and overwhelmed, most of them eventually left.

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 “ultimatum.”

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 “proposers” ought to offer the least they can get away with—namely, one dollar. Of course, a moment’s thought quickly suggests why people play the way they do—namely that it doesn’t 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 you’re not alone. If anything seems like common sense, it’s that people care about fairness as well as money—sometimes 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 “hyperfair” offers tended to get rejected just as frequently as unfair offers.
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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 “mapped” the unfamiliar interaction onto the most similar social exchange they could think of—which happened to be gift exchange—and responded accordingly. Thus what might have seemed like free money to a Western participant looked to an Au or Gnau participant very much like an unwanted obligation. The Machiguenga, by contrast, live in a society in which the only relationship bonds that carry any expectation of loyalty are with immediate family members. When playing the ultimatum game with a stranger, therefore, Machiguenga participants—again mapping the unfamiliar onto the familiar—saw little obligation to make fair offers, and experienced very little of the resentment that would well up in a Western player upon being presented with a split that was patently unequal. To them, even low offers were seen as a good deal.

Once you understand these features of Au, Gnau, and Machiguenga cultures, their puzzling behavior starts to seem entirely reasonable—commonsense even. And that’s exactly what it was. Just as we reflexively regard fairness and reciprocity as commonsense principles in our world that should be respected in general, and should be defended when violated without good reason, so the people of the fifteen preindustrial societies have their own implicit set of understandings about how the world is supposed to work. Those understandings might be different from ours. But once they have been accepted, their commonsense logic works in exactly the same way as ours does. It is simply what any reasonable person would do if they had grown up in that culture.

What these results reveal is that common sense is “common” only to the extent that two people share sufficiently
similar social and cultural experiences. Common sense, in other words, depends on what the sociologist Harry Collins calls collective tacit knowledge, meaning that it is encoded in the social norms, customs, and practices of the world.
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According to Collins, the acquisition of this type of knowledge can be learned only by participating in society itself—and that’s why it is so hard to teach to machines. But it also means that even among humans, what seems reasonable to one might seem curious, bizarre, or even repugnant to another. For example, as Clifford Geertz, the anthropologist, has described, the treatment of hermaphroditic children has varied dramatically across different times and cultures. The Romans abhorred and killed them; the Greeks tolerated them; the Navajo revered them; and the east African Pokot tribe regarded them simply as “mistakes,” to be kept around or discarded in the same way they might keep or throw out a flawed pot.
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Likewise, practices including human slavery, sacrifice, cannibalism, foot binding, and female genital mutilation that are reviled in most contemporary cultures have all been (and in some cases, still are) considered entirely legitimate in different times and places.

Another important consequence of the socially embedded nature of common sense is that disagreements over matters of common sense can be surprisingly difficult to resolve. For example, it may seem remarkable to people who have grown up with the impression that New York is a crime-ridden cesspool, or at the very least a cold, hard-edged city full of people you can’t trust, that, according to a recent news story, there is a small cadre of Manhattan residents who don’t lock their doors. As the article makes clear, most people in the city think that the “no lock people” are crazy. As one woman said, “I live in a high-rise with a doorman, I’ve been there fifteen years, and I’ve never heard of a burglary in the building. But
that has absolutely nothing to do with it—it’s common sense [to lock your door].” Yet the only thing that seems shocking to the people who don’t lock their doors is that anyone else would be shocked by it.
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What’s curious about this story is that the language of the people involved almost precisely mirrors the experiences of Geertz, who noted in his study of witchcraft in Java that “when the whole family of a Javanese boy tells me that the reason he has fallen out of a tree and broken his leg is that the spirit of his deceased grandfather pushed him out because some ritual duty toward the grandfather has been inadvertently overlooked, that, so far as they are concerned, is the beginning, the middle, and the end of the matter: it is precisely what they think has occurred, it is all they think has occurred, and they are puzzled only at my puzzlement at their lack of puzzlement.” Disagreements over matters of common sense, in other words, are hard to resolve because it’s unclear to either side on what grounds one can even conduct a reasonable argument. Whether the issue is a Western anthropologist discussing witchcraft with preindustrial tribes in Indonesia, New Yorkers disagreeing about door locks, or the NRA disagreeing with the Brady Campaign over the sorts of guns that Americans ought to be able to buy, whatever it is that people believe to be a matter of common sense, they believe it with absolute certainty. They are puzzled only at the fact that others disagree.
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That what is self-evident to one person can be seen as silly by another should give us pause about the reliability of common sense as a basis for understanding the world. How can we be confident that what we believe is right when someone else
feels equally strongly that it’s wrong—especially when we can’t articulate why we think we’re right in the first place? Of course, we can always write them off as crazy or ignorant or something and therefore not worth paying attention to. But once you go down that road, it gets increasingly hard to account for why we ourselves believe what we do. Consider, for example, that since 1996 support among the general public for allowing same-sex couples to marry has almost doubled, from 25 percent to 45 percent.
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Presumably those of us who changed our minds over this period do not think that we were crazy fourteen years ago, but we obviously think that we were wrong. So if something that seemed so obvious turned out to be wrong, what else that we believe to be self-evident now will seem wrong to us in the future?

Once we start to examine our own beliefs, in fact, it becomes increasingly unclear even how the various beliefs we espouse at any given time fit together. Most people, for example, consider their own views about politics to be derived from a single coherent worldview: “I’m a moderate liberal” or “I’m a diehard conservative,” and so on. If that were true, however, then one would expect that people who identify as liberals would tend to espouse the “liberal” perspective on most matters, and that conservatives would espouse a consistently different view. Yet research finds that regardless of whether people identify themselves as liberals or conservatives, what they think about any one issue, like, say, abortion, has relatively little relation to what they believe about other issues, such as the death penalty or illegal immigration. In other words, we have the impression that our particular beliefs are all derived from some overarching philosophy, but the reality is that we arrive at them quite independently, and often haphazardly.
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