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By Root 986 0

” 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 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.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 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.

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 “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