Being Wrong - Kathryn Schulz [58]
Human beings, on the other hand, have no trouble answering these questions, because we don’t care about what is logically valid and theoretically possible. We care about what is probable. We determine what is probable based on our prior experience of the world, which is where evidence comes in: we choose the most likely answer to any given question based on the kinds of things we have (and haven’t) experienced in comparable situations before. Over the course of our lifetimes, we’ve observed some things about giraffes, sentences, and sentences about giraffes, and based on those observations, we make an educated guess about this particular sentence concerning this particular giraffe. Significantly, it doesn’t matter how much we’ve observed about sentences and giraffes. Unlike Descartes, we aren’t interested in whether we have ample evidence to support a given conclusion—which is just as well, since, as the computer’s conundrum shows, we almost certainly do not. All we’re interested in is whether whatever evidence we do have supports one conclusion better than another. That’s why four-year-olds can answer this question, despite their comparatively limited experience with sentences and (one assumes) even more limited experience with giraffes.
This strategy of guessing based on past experience is known as inductive reasoning. As we’ve seen, inductive reasoning makes us vastly better than computers at solving problems like the ones in this quiz. But it also makes people like Descartes nervous, because it means that our beliefs are not necessarily true. Instead, they are probabilistically true. This point was made (and made famous) by the philosopher David Hume, who was arguably the first thinker to fully grasp both the import and the limitation of inductive reasoning. To borrow his much-cited example: How can I be sure that all swans are white if I myself have seen only a tiny fraction of all the swans that have ever existed? If the world were always uniform, consistent, and predictable, I could trust that I am right about this induction (and about all inductions). Unfortunately, as Hume noted, nothing in logic requires the world to be that way, and we know from experience that it isn’t always so. I can keep my eyes open for more white swans, but no matter how many I spot, I’ll only be adding to my body of evidence, rather than actually proving something about the necessary color scheme of swans. In other words, inductions are necessarily impossible to substantiate. We can know that they are wrong—as Hume’s example turned out to be, when a species of black swan was discovered in Australia after his death—but we can’t know that they are right. All we know is that they are at least somewhat more likely to be right than the next best guess we could make.
When it comes to multiple-choice quizzes, we are all comfortable with the idea that we make the best guess we can based on whatever evidence we already have. We ought to be, since we’ve been doing so since grade school. But our use of inductive reasoning isn’t limited to that kind of low-stakes situation. On the contrary: psychologists and neuroscientists increasingly think that inductive reasoning undergirds virtually all of human cognition. You make best guesses based on your cumulative exposure to the evidence every day, both unconsciously (as when the motor fibers in your arm estimate where to swing for a baseball) and consciously (as when you bet against the Red Sox, and on the best time to tell your partner how much you lost on that bet).
This kind of guesswork is also how you learned almost everything you know about the world. Take language. Your parents didn’t teach you to talk by sitting you down and explaining that English is a subject-verb-object language, that most verbs are converted to the past tense by adding the suffix “-ed,” that adjectives generally go before the nouns they modify, and so forth. Mercifully for everyone involved, they didn’t have to. All they had to do was keep on chatting about how Mommy poured the milk and Laura painted