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?
Kuhn’s focus on persuasion is telling. He is not interested in how Lavoisier and Galileo arrived at more accurate paradigms, because he does not believe one idea is more truthful than another. Instead, he delves into the human element of scientific change.
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.
Here, Kuhn compares paradigm shifts to Charles Darwin’s theory of evolution through natural selection (a comparison he will repeat at the end of the book). This comparison suggests that new scientific theories emerge not in spite of context but because of it—at a given moment, a given idea might be best adapted to solve problems and convince other scientists of its validity.
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.
In the theory of natural selection, some species triumph over others because they are able to hoard or steal resources from their fellows creatures. In the same way, new scientific theories succeed not only because they are successful but because they point out their competitors’ failures.
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.
Earlier, Kuhn has argued that if different paradigms entail different experiences of the world, scientists working in different paradigms are also working in separate universes. In this way, they fail “to make complete contact” with one another; Kuhn refers to this conflict as the “incommensurability” of different paradigms. This clash then makes it difficult for scientists to persuade people whose very lived experience is at odds with their own.
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.”
In his discussion of textbooks, Kuhn emphasizes that many paradigms use the same word to signify different ideas. Here, he demonstrates just how unreliable and “partial” language is. This linguistic failure also helps illustrate why tacit knowledge is such an important bonding force for scientific communities.
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.”
There are several important things to note in this passage: first, Kuhn again emphasizes that paradigm shifts are instinctual and almost illogical. Second, Kuhn again asserts that the gap between scientists in paradigms is not just theoretical but experiential. And most fascinatingly, Kuhn expresses his own intuition here—in confessing that he is “unable to explicate further,” Kuhn shows his own humanity to his readers (just as he often points out scientists’ humanity).
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.”
Just as many paradigm shifts are initiated by people who are very young or new to their field, established scientists have the most trouble with such a radical change in their beliefs. For many such people, a true shift in mindset is impossible; Kuhn believes it is more likely that these people will die than that they will be persuaded.
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.
Kuhn has repeatedly highlighted scientists’ emotions and biases as important aspects of their worldviews—and, consequently, their work. But in using the word “conversion,” he blurs the line between objective science and internal spirituality (paralleling his earlier comparison of science to “myth”).
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).
Surprisingly, rather than critiquing scientists’ belief systems, Kuhn suggests that this kind of personal perspective is an essential ingredient of new discovery. So, while Kuhn pushes back against the narrative that science is objective, he also celebrates scientists’ subjectivity.
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.
As Kuhn demonstrated in the case of John Dalton’s atomic theory, many paradigms initially begin more with predictions than with evidence. When reality conforms to a theory’s prediction, it is only natural that such a theory becomes newly awe-inspiring, gaining converts who might have scoffed initially.
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.
Aesthetics are a crucial part of art and literature, but rarely is science discussed in aesthetic terms. By arguing that the style and simplicity of a given theory matters, Kuhn once again shows how scientific change is driven more by a community’s preferences and less by a single, objective truth.
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.
Again, Kuhn focuses on the group mentality that allows scientists to collaborate with one another; it is easier for scientists to adopt new ideas as a group than as individuals. Equally important, however, is the fact that this shift is about social and intuitive knowledge, not about logic—in fact, Kuhn implies that it is almost more logical for scientists to resist new paradigms than it is for them to convert.