When people compared one thing to another—two people, two places, two numbers, two ideas—they did not pay much attention to symmetry. To Amos—and to no one else before Amos—it followed from this simple observation that all the theories that intellectuals had dreamed up to explain how people made similarity judgments had to be false. “Amos comes along and says you guys aren’t asking the right question,” says University of Michigan psychologist Rich Gonzalez. “What is distance? Distance is symmetric. New York to Los Angeles has to be the same distance as Los Angeles to New York. And Amos said, ‘Okay, let’s test that.’” If, on some mental map, New York sits a certain distance from Tel Aviv, Tel Aviv must sit precisely the same distance from New York. Yet you needed only to ask people to see that it did not: New York was not as much like Tel Aviv as Tel Aviv was like New York. “What Amos worked out was that whatever is going on is not a distance,” says Gonzalez. “In one swoop he basically dismissed all theories that made use of distance. If you have a distance concept in your theory you are automatically wrong.”
Amos had his own theory, which he called “features of similarity.”? He argued that when people compared two things, and judged their similarity, they were essentially making a list of features. These features are simply what they notice about the objects. They count up the noticeable features shared by two objects: The more they share, the more similar they are; the more they don’t share, the more dissimilar they are. Not all objects have the same number of noticeable features: New York City had more of them than Tel Aviv, for instance. Amos built a mathematical model to describe what he meant—and to invite others to test his theory, and prove him wrong.
Many have tried. Before he traveled to Stanford in the 1980s to study for his doctorate with Amos, Rich Gonzalez had read “Features of Similarity” several times. Upon arrival, he found his way to Amos’s office, introduced himself, and asked what he thought was a killer question: “What about a three-legged dog?” Two three-legged dogs are obviously more similar to each other than a three-legged dog is to a four-legged dog. Yet a three-legged dog shares exactly the same number of features with a four-legged dog as it does with a three-legged dog. Ergo, an exception to Amos’s theory! “I went in thinking, ‘I’m outsmarting Amos,’” recalls Gonzalez. “He just looked at me like, Really? That’s the best you can come up with? I think there might have been an initial glare, but then he was nice about it—and he said, ‘The absence of a feature is a feature.’” Amos had written that into his original paper. “Similarity increases with the addition of common features and/or deletion of distinctive features.”
From Amos’s theory about the way people made judgments of similarity spilled all sorts of interesting insights. If the mind, when it compares two things, essentially counts up the features it notices in each of them, it might also judge those things to be at once more similar and more dissimilar to each other than some other pair of things. They might have both a lot in common and a lot not in common. Love and hate, and funny and sad, and serious and silly: Suddenly they could be seen—as they feel—as having more fluid relationships to each other. They weren’t simply opposites on a fixed mental continuum; they could be thought of as similar in some of their features and different in others. Amos’s theory also offered a fresh view into what might be happening when people violated transitivity and thus made seemingly irrational choices.
When people picked coffee over tea, and tea over hot chocolate, and then turned around and picked hot chocolate over coffee—they weren’t comparing two drinks in some holistic manner. Hot drinks didn’t exist as points on some mental map at fixed distances from some ideal. They were collections of features. Those features might become more or less noticeable; their prominence in the mind depended on the context in which they were perceived. And the choice created its own context: Different features might assume greater prominence in the mind when the coffee was being compared to tea (caffeine) than when it was being compared to hot chocolate (sugar). And what was true of drinks might also be true of people, and ideas, and emotions.
The idea was interesting: When people make decisions, they are also making judgments about similarity, between some object in the real world and what they ideally want. They make these judgments by, in effect, counting up the features they notice. And as the noticeability of features can be manipulated by the way they are highlighted, the sense of how similar two things are might also be manipulated. For instance, if you wanted two people to think of themselves as more similar to each other than they otherwise might, you might put them in a context that stressed the features they shared. Two American college students in the United States might look at each other and see a total stranger; the same two college students on their junior year abroad in Togo might find that they are surprisingly similar: They’re both Americans!
By changing the context in which two things are compared, you submerge certain features and force others to the surface. “It is generally assumed that classifications are determined by similarities among the objects,” wrote Amos, before offering up an opposing view: that “the similarity of objects is modified by the manner in which they are classified. Thus, similarity has two faces: causal and derivative. It serves as a basis for the classification of objects, but is also influenced by the adopted classification.” A banana and an apple seem more similar than they otherwise would because we’ve agreed to call them both fruit. Things are grouped together for a reason, but, once they are grouped, their grouping causes them to seem more like each other than they otherwise would. That is, the mere act of classification reinforces stereotypes. If you want to weaken some stereotype, eliminate the classification.
Amos’s theory didn’t exactly contribute to the existing conversation about how people made judgments of similarity. It took over the entire conversation. Everyone else at the party just circled around Amos and listened. “Amos’s approach to doing science wasn’t incremental,” said Rich Gonzalez. “It proceeded by leaps and bounds. You find a paradigm that is out there. You find a general proposition of that paradigm. And you destroy it. He saw himself doing a negative style of science. He used the word a lot: negative. This turns out to be a very powerful way of doing social science.” That’s how Amos would begin: by undoing the mistakes of others. As it turned out, other people had made some other mistakes.
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* When B. F. Skinner discovered as a young man that he would never write the great American novel, he felt a despair that he claimed nearly drove him into psychotherapy. The legendary psychologist George Miller claimed that he gave up his literary ambition for psychology because he had nothing to write about. Who knows what mixed feelings William James experienced when he read his brother Henry’s first novel? “It would be interesting to ask how many psychologists come up short next to great writers who happen to be near them,” one prominent American psychologist has said. “It may be the fundamental driver.”
? A paper by this name did not appear until 1977, but it grew from ideas he’d formed a decade earlier as a graduate student.
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