"Look," says Thomas Kuhn. The word seems to signal that Kuhn thinks his listener has misunderstood him, or is in danger of doing so, and he, Kuhn, is going to try--probably in vain--to set the terribly complicated record straight. Kuhn utters the word often.

"Look," he says again. He leans his gangly frame and long face forward, and his big lower lip, which ordinarily curls up amiably at the corners, sags. "For Christ's sake, if I had my choice of having written the book or not having written it, I would choose to have written it. But there have certainly been aspects involving considerable upset about the response to it."

"The book" is The Structure of Scientific Revolutions, commonly called the most influential treatise ever written on how science does (or does not) proceed. Since its publication in 1962, it has sold nearly a million copies in 16 languages, and it is still fundamental reading in courses on the history and philosophy of science.

The book is notable for having spawned that trendy term "paradigm." It also fomented the now trite idea that personalities and politics play a large role in science. Perhaps the book's most profound argument is less obvious: scientists can never fully understand the "real world" or even--to a crucial degree--one another.

Given this theme, one might think that Kuhn, a 68-year-old professor of philosophy and history of science at the Massachusetts Institute of Technology, would have expected his own ideas to be misunderstood. But he still seems pained by the breadth of misunderstanding, by the persistent claims, for example, that he thinks scientists are "irrational." "If they had said 'arational,' I wouldn't have minded at all," he remarks with no trace of a smile.

Kuhn's fear of compounding the confusion over his work has made him a bit press-shy. Although he finally agrees to talk to Scientific American about his career (after unburdening himself of the fact that in 1964 this magazine gave Structure "the worst review I can remember"), he must point out the pitfalls of the exercise. "One is not one's own historian," he warns, "let alone one's own psychoanalyst."

Kuhn nonetheless traces his view of science to a single "Eureka!" moment in 1947. He was working toward his doctorate in physics at Harvard University when he was asked to teach some science to undergraduate humanities majors. Searching for a simple case history that could illuminate the roots of Newtonian mechanics, Kuhn opened Aristotle's Physics and was astonished at how "wrong" it was. How could someone so brilliant on other topics be so misguided in physics? Kuhn was pondering this mystery, staring out of the window of his dormitory room ("I can still see the vines and the shade two thirds of the way down"), when suddenly Aristotle "made sense."

Kuhn realized that Aristotle's views of such basic concepts as motion and matter were totally unlike Newton's. Aristotle used the word "motion," for example, to refer not just to change in position but to change in general--the reddening of the sun as well as its descent toward the horizon. Understood on its own terms, Aristotle's physics "wasn't just bad Newton," Kuhn says; it was just different.

Although Kuhn went on to receive a doctorate in physics, he switched shortly thereafter to the history of science, intending to explore the mechanisms behind scientific change. He wrestled with the ideas awakened in him by Aristotle for 15 years--during which he also wrote a history of the Copernican revolution and left Harvard for the University of California at Berkeley--before he finished Structure. "I sweated blood and blood and blood," he says, "and finally I had a breakthrough."

The breakthrough was the concept of paradigm. "Paradigm," pre-Kuhn, referred simply to an example (often, one used to teach a language, such as amo, amas, amat in Latin). In Structure, Kuhn defines the word most narrowly as an archetypal experiment or "problem solution"--such as Galileo's (probably apocryphal) Tower of Pisa demonstration or the two-slit experiment showing light's particle/wave nature--that implicitly tells scientists how to look at the world. Scientists erect elaborate systems of theory and methodology on a paradigm (in Structure, Kuhn occasionally refers to such systems as paradigms as well), but these systems can never be formally explicated. They rest ultimately on scientists' subjective views of the paradigmatic experiment.

Scientists, as Kuhn describes them, are deeply conservative. Once indoctrinated into a paradigm, they generally devote themselves to solving "puzzles," problems whose solutions reinforce and extend the scope of the paradigm rather than challenging it. Kuhn calls this "mopping up." But there are always anomalies, phenomena that the paradigm cannot account for or that directly contradict it. Anomalies are often ignored. But if they accumulate, they may trigger a revolution (also called a paradigm shift, although not originally by Kuhn), in which scientists abandon the old paradigm for a new one.

Denying the view of science as a continual building process, Kuhn asserts that a revolution is a destructive as well as a creative event. The proposer of a new paradigm stands on the shoulders of giants and then bashes them over the head. He or she is often young or new to the field, that is, not fully indoctrinated.

Most scientists make reluctant revolutionaries. They often do not understand a new paradigm, and they have no objective "rules" by which to judge it. (If such rules existed, computers could do the judging.) In a sense, different paradigms--like Newton's and Aristotle's physics--have no common standard for comparison; they are "Incommensurate," to use Kuhn's term. Proponents of different paradigms can argue forever without resolving their differences because they invest basic terms--motion, particle, time, space--with different meanings.

The "conversion" of scientists is thus both a subjective and a political process. It may involve sudden, intuitive understanding--like that finally achieved by Kuhn as he pondered Aristotle. Yet scientists often adopt a paradigm simply because it is backed by others with strong reputations or by a majority of the community.

The new paradigm may solve puzzles better than the old one does, and it may also yield more practical applications. But that does not mean it is a truer reflection of reality, according to Kuhn. He also rejects the notion, promulgated by Karl Popper (perhaps Kuhn's greatest rival in the philosophy of science), of falsification. The real world is unknowable, and propositions are true or false only within the context of a particular paradigm, Kuhn asserts.

The book triggered diverse reactions. Most "hard" scientists shrugged and went about their business. But many in the soft, or social, sciences "loved" the book, Kuhn says, perhaps because it offered hope that they could attain the same level of legitimacy (or illegitimacy) as physicists or chemists. "Some of them even said, 'Wow, now all we have to do is figure what our paradigm is and enforce it,'" Kuhn explains.

Some philosophers, on the other hand, deplored Kuhn's brusque dismissal of empiricism and objective truth. He was accused of claiming that science is nothing more than "power politics" or "mob psychology." "Look, I think that's nonsense, and I'm prepared to argue that," Kuhn says heatedly.

Kuhn has been even more distressed by those who admiringly misinterpret him. "I've often said I'm much fonder of my critics than my fans," he comments. In the 1960s, his work was seized on by radicals opposed to science and its offspring, technology, and indeed to any "cognitive authority" that might distort "pure experience." Kuhn recalls students telling him, "Oh, thank you, Mr. Kuhn, for telling us about paradigms. Now that we know about them, we can get rid of them."

Kuhn's protests were to no avail. In one seminar, he notes, the professor and students were discussing "how my book denied the idea of truth and falsity." Kuhn tried to explain that within the context of a paradigm, truth and falsity were perfectly valid and indeed necessary concepts, but the professor cut him off, saying, "'You don't know how radical this book is.'"

Some of these students are now perhaps members of a new school in anthropology that analyzes science from a "post-Kuhnian" perspective. The goal of this "burgeoning" discipline, according to a recent essay in Current Anthropology, is "a radical deconstruction of traditionally conceived foundations of scientific knowledge that casts doubt on all fields of scholarship with scientific pretensions." "'Deconstruction' is for me a dirty word," Kuhn says, "although I'm sure that's largely because I don't know what it's about."

Kuhn concedes that he is partly to blame for some of the anti-science interpretations of his book. After all, in Structure he does call scientists "addicts" at one point. He compares their adherence to paradigms to religious faith, and likens their education to the brainwashing described by Orwell in his totalitarian novel 1984. Kuhn also acknowledges that the terms "puzzle" and "mopping up" may sound a bit condescending. "I won't retreat from them for a moment, but maybe I should have said more about the glories of puzzle solving."

Kuhn points out, just for the record, that he is in fact pro-science. He is also pro-paradigms. They provide the secure foundation needed for scientists to organize the chaos of experience and to solve ever more complex puzzles. It is the conservatism of science, its rigid adherence to paradigms, he insists, that enables it to produce "the greatest and most original bursts of creativity" of any human enterprise.

In 1964 Kuhn left Berkeley for the calmer surroundings of Princeton University. After trying for several years to maintain a dignified silence on Structure, he finally wrote several essays attempting to explain what he really meant. In particular, he tried to reclaim "paradigm." Like a virus, the word had spread beyond the history and philosophy of science and infected the intellectual community at large, where it came to mean virtually any dominant idea.

A 1974 New Yorker cartoon captured the phenomenon: a woman gushes to a smirking man, "Dynamite, Mr. Gerston! You're the first person I ever heard use 'paradigm' in real life." Again, Kuhn admits the fault is partly his, for making the "dreadful mistake" of letting paradigm denote not only an archetypal experiment but also "the entire constellation of beliefs, values and techniques" that binds a scientific community together. (One philosopher actually counted 21 different implicit meanings for "paradigm" in Structure.)

In one essay, Kuhn introduced the term "exemplar" to replace paradigm in its narrow sense, but it never caught on. Eventually he gave up. "Look, if you've got a bear by the tail," he says, "there comes a point at which you've got to let it go and stand back." (Paradigm abuse continues: last year a White House bureaucrat, James P. Pinkerton, gained the spotlight by calling old Reaganomics "The New Paradigm.")

In 1978 Kuhn published a relatively straightforward history of science: Black-Body Theory and the Quantum Discontinuity, 1894-1912. The book argues that the concept of quantum discontinuity was first explicated not by Max Planck, as is commonly believed, but by Einstein and Paul Ehrenfest. Kuhn thinks the book, his fifth and most recent, is "in some ways my finest work." Yet some physicists accused him of unfairly bolstering Einstein's already unparalleled reputation at Planck's expense. And although Kuhn says the book embodies Structure's ideas, some readers were disappointed that he did not reexamine those issues explicitly.

Shortly thereafter, Kuhn left Princeton for M.I.T., where he is now toilling over another book. He says it will "probably" take up two issues raised In Structure. One is the concept of incommensurability, the breakdown of communication that occurs between adherents of different paradigms. The other issue has to do with the similarity of the evolution of science and the evolution of living organisms.

Kuhn draws this analogy at the very end of Structure. He notes that evolution occurs not toward anything--toward the truth in the case of science, or toward that paragon of wisdom and nobility Homo sapiens in the case of biological evolution--but only away from something. Moreover, just as species tend to proliferate and to become more specialized over time, Kuhn suggests, so do scientific fields, each committed to its own paradigm.

What do these ideas imply about the future of science? Will it resemble a symphony descending into dissonance, a mirror fracturing into ever smaller shards? Is this the disturbing possibility Kuhn's new work will explore? Wincing, Kuhn declines to discuss the book further. "Look," he says, "I don't want these ideas being abused before they're even published."

Note: This is a very important reading, so you will need to go over it several times.

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