Story of Psychology - Morton Hunt [359]
Inductive reasoning: By contrast, inductive reasoning is loose and inexact. It moves from specific beliefs to broader ones, that is, from limited cases to generalizations. From “Socrates is mortal,” “Aristotle is mortal,” and other instances, one infers, with a degree of confidence based on the number of cases, that “all men are mortal,” although even a single case to the contrary would invalidate that conclusion.
A good deal of important human reasoning is of this type. Categorization and concept formation, crucial to thinking, are the products of induction, as seen in studies of how children arrive at categories and concepts. All the higher knowledge humankind possesses about the world—everything from the inevitability of death to the laws of planetary motion and galactic formation—is the product of the derivation of generalizations from a mass of particulars.
Induction is also the reasoning used where pattern recognition is the key to solving a problem. A simple example:
What number comes next?
2 3 5 6 9 10 14 15 ——
A ten-year-old can answer correctly after a while; an adult can see the pattern and the answer (20) in a minute or less. It is the very reasoning process employed by economists, public health officials, telephone system planners, and many others whose recognition of patterns is critically important to the survival of modern society.
(Disconcertingly, researchers have found that many people frequently fail to reason inductively from incoming information. All too often, we notice and add to our memory store only what supports a strongly held belief, ignoring any that does not. Psychologists call this “confirmation bias.” Dan Russell and Warren Jones gave subjects materials to read, some confirming and some disproving the existence of ESP. Afterward, believers in ESP remembered the confirming materials 100 percent of the time but the negative materials only 39 percent of the time, while skeptics remembered both kinds about 90 percent of the time.81)
Much of our reasoning combines deduction and induction, each of which serves its own purposes. How we came by both kinds of reasoning ability has been explained, at least hypothetically, by evolutionary psychology: Both methods are assets in the struggle to survive and were the products of natural selection.82 The hypothesis seems validated by a recent study using PET scans: When subjects were asked to solve problems requiring deduction, two small areas on the right side of the brain showed increased activity; when the problems required inductive thinking, two brain structures on the left side showed it.83 Natural selection, in short, developed brain structures capable of both kinds of reasoning.
Probabilistic reasoning: The human mind’s abilities are the product of evolutionary selection, but we have lived in advanced civilized societies too short a time to have developed an inherited ability for sound reasoning about statistical likelihoods, though it is often called for in modern life.
Daniel Kahneman and Amos Tversky, who did much of the basic work in this area, asked a group of subjects which they would prefer: a sure gain of $80, or an 85 percent chance of winning $100 along with a 15 percent chance of winning nothing. Most people preferred the sure gain of $80, although statistically the average yield of the risky choice is $85. Kahneman and Tversky concluded that people are “risk-averse”: They prefer a sure thing even when a risky thing is the better bet.
Turning to the obverse situation, Kahneman and Tversky asked another group of subjects whether they would prefer a sure loss of $80 or an 85 percent chance of losing $100 along with a 15 percent chance of losing nothing. This time a large majority preferred the gamble to the sure thing even though, on average, the gamble is costlier. Kahneman and Tversky