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Steven Pinker -- How the Mind Works - Hampshire High Italian ...

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Good Ideas 351give numbers to single events, <strong>the</strong>y may switch to a third, nonma<strong>the</strong>maticaldefinition of probability, "degree of belief warranted by <strong>the</strong>information just presented." That definition is found in many dictionariesand is used in courts of law, where it corresponds to conceptssuch as probable cause, weight of evidence, and reasonable doubt. Ifquestions about single-event probabilities nudge people into that definition—anatural interpretation for subjects to have made if <strong>the</strong>yassumed, quite reasonably, that <strong>the</strong> experimenter had included <strong>the</strong>sketch of Linda for some purpose—<strong>the</strong>y would have interpreted <strong>the</strong>question as, To what extent does <strong>the</strong> information given about Lindawarrant <strong>the</strong> conclusion that she is a bankteller? And a reasonableanswer is, not very much.A final mind-bending ingredient of <strong>the</strong> concept of probability is <strong>the</strong>belief in a stable world. A probabilistic inference is a prediction todaybased on frequencies ga<strong>the</strong>red yesterday. But that was <strong>the</strong>n; this is now.<strong>How</strong> do you know that <strong>the</strong> world hasn't changed in <strong>the</strong> interim? Philosophersof probability debate whe<strong>the</strong>r any beliefs in probabilities are trulyrational in a changing world. Actuaries and insurance companies worryeven more—insurance companies go bankrupt when a current event or achange in lifestyles makes <strong>the</strong>ir tables obsolete. Social psychologistspoint to <strong>the</strong> schlemiel who avoids buying a car with excellent repair statisticsafter hearing that a neighbor's model broke down yesterday.Gigerenzer offers <strong>the</strong> comparison of a person who avoids letting his childplay in a river with no previous fatalities after hearing that a neighbor'schild was attacked <strong>the</strong>re by a crocodile that morning. The differencebetween <strong>the</strong> scenarios (aside from <strong>the</strong> drastic consequences) is that wejudge that <strong>the</strong> car world is stable, so <strong>the</strong> old statistics apply, but <strong>the</strong> riverworld has changed, so <strong>the</strong> old statistics are moot. The person in <strong>the</strong>street who gives a recent anecdote greater weight than a ream of statisticsis not necessarily being irrational.Of course, people sometimes reason fallaciously, especially in today'sdata deluge. And, of course, everyone should learn probability and statistics.But a species that had no instinct for probability could not learn <strong>the</strong>subject, let alone invent it. And when people are given information in aformat that meshes with <strong>the</strong> way <strong>the</strong>y naturally think about probability,<strong>the</strong>y can be remarkably accurate. The claim that our species is blind tochance is, as <strong>the</strong>y say, unlikely to be true.

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