The Structure of Scientific Revolutions

Kuhn now turns his attention to scientists who have truly discovered something new (like Copernicus, Galileo, and Lavoisier). How did these men persuade their colleagues and ensure that their paradigms were the successful ones?

In moments of crisis, scientists begin to test out the old paradigm to see if it holds up against various anomalies. At the same time, they begin to compare this old paradigm to the new theory (or theories) that are threatening to replace it. But again, these tests do not lead to one perfect, completely accurate theory. Instead, as Kuhn writes, “verification is like natural selection: it picks out the most viable among the actual alternatives,” even though more useful ideas may just have yet to be thought up. In other words, the winning theory is not the best theory; it is just the theory most able to persist.

Historian Karl Popper believes that it is falsification of theories—and not verification—that determines which paradigm will flourish. Kuhn sees Popper’s idea of falsification as another way of talking about anomalies (and the crises that come from them). In that case, Kuhn imagines a “two-stage formulation” in which theories compete both by verifying themselves and by falsifying their competitors.  

Paradigm verification is never so simple, however. Each worldview has such different basic assumptions that often, paradigms are “bound partly to talk through each other,” failing “to make complete contact.” Moreover, each paradigm tries to “banish” questions that the other ones hold dear. For example, Newton claimed it was unimportant to understand why certain attractive forces existed; Einstein’s relativity tried, above all else, to solve exactly the problem that Newton ignored.

Moreover, because each new competing theory borrows—and alters—some concepts and techniques from the old theory, proponents of different theories are using the same language to talk about contrasting ideas. There is always “misunderstanding,” then, between the competing paradigms, and Kuhn is firm that “communication across the revolutionary divide is inevitably partial.”

Most importantly, it is difficult to compare paradigms because of something Kuhn struggles to define. “In a sense that I am unable to explicate further,” he explains, “the proponents of competing paradigms practice their trades in different worlds.” Some of the concepts in each paradigm are believed or intuited and so cannot always be proved by logic. “Like the gestalt switch,” in which a bird suddenly appears as an antelope, “it must occur all at once, or not at all.”

Indeed, most new paradigms do not take hold while their creators are still alive. Charles Darwin (who first conceptualized evolution) and Max Planck (who pioneered quantum physics) acknowledged as much in their treatises. Planck even wrote that “a new scientific truth does not triumph by convincing its opponents […] but rather because its opponents eventually die.”

But rather than seeing this miscommunication as evidence of scientists’ stubbornness, Kuhn believes that a paradigm shift is “a conversion experience that cannot be forced.” If normal science is effective because it gives scientists confidence in their beliefs, then uprooting those beliefs in a paradigm shift is necessarily difficult.

It is impossible to generalize about why some scientists are eventually persuaded. But Kuhn is careful to note that “conversions occur not despite the fact that scientists are human but because they are.” The most effective claim, however, seems to be that the new paradigm can solve the problems that caused the old one to collapse (e.g., Newton could use his theory to make much more accurate quantitative predictions about stars and planets).

However, this claim to effectiveness is not enough by itself. And in fact, it is not always true—Copernicus’s measurements of the heavens were not any more accurate or useful than Ptolemy’s. In these cases, theories often gain converts many years after they are thought up, when an unexpected phenomenon seems to affirm them. For example, Copernicus had been dead for 60 years when a new kind of telescope proved many of his hypotheses. Einstein was luckier: in his own lifetime, his theory was born out by the planet Mercury’s motion.

Finally, some paradigms succeed because they are almost aesthetically pleasing in their neatness. This is especially important because accepting a new paradigm often requires a leap of faith; usually, the theory does not yet have the evidence to back it up.  Aesthetic considerations—when the paradigm is simple to use or easy to understand—therefore help people take this leap of faith.

If an individual’s initial conception of the paradigm is a “lightning flash,” the persuasion stage is much slower. Not all scientists are persuaded at once. Instead, members of the profession gradually shift, and as support for the paradigm grows, additional scientists are less cautious about joining in. Yet Kuhn maintains that while it might be unreasonable for scientists to resist new paradigms forever, it is never illogical for them to do so.