Kuhn explains his choice of the word “revolution,” which immediately suggests a parallel to politics. In fact, scientific revolutions are akin to political revolutions in that both see communities beginning to doubt or grow frustrated with established institutions. Moreover, in a political revolution, one set of institutions replaces another—but only after a temporary gap when society is not governed. The same could be said of the gaps between scientific paradigms, when science retreats to a pre-paradigm version of itself.
Because science is so often viewed as objective, consent and community are not often talked about in regard to scientific discovery. But here, Kuhn suggests that just as governments rely on the will of the people, scientific ideas can only exist when enough members of the field endorse them. When scientists abandon a paradigm, then, it is comparable to when citizens renounce their government—and it brings the same period of chaos that a political revolution would.
Most importantly, when a new political power assumes control, they must do so by persuading the populace. In science, the replacement paradigm will not be entirely correct, just as its predecessor had some holes. Rather, the new paradigm wins because it is the most persuasive: “there is no higher standard” for either a paradigm or a government “than the assent of the relevant community.” It matters, then, that scientists are persuasive in the way they talk about their work and discoveries.
Kuhn’s focus on persuasion here is noteworthy. If science were making a linear march toward the truth, persuasion would be irrelevant; each theory would naturally succeed and build on the last. But by focusing on the human and communal aspects of scientific progress, Kuhn also calls attention to the ways in which personality and chance—not objective truth—affect the history of science.
This persuasive element of scientific revolutions then helps explain why they are not cumulative. In order to have a convincing new theory, that theory must reject the aspects of the previous theory that contradict it—therefore making it almost impossible for one paradigm to build on another. However, very few people share Kuhn’s belief that each paradigm is incompatible with the one that came before it.
Kuhn has argued that new theories emerge when old theories are broken, so it follows proponents of the new paradigm must work to destroy the old. Here, Kuhn draws a clear distinction between the popular, linear view of science and his own, which is circular and non-cumulative.
At the same time, old paradigms still offer important answers. This is true both of Newtonian physics, which is still widely respected, and of phlogiston chemistry, which is now mostly scoffed at. Kuhn argues that rather than linking these theories to the theories that replaced them, historians should acknowledge that the theories were successful in answering one specific set of questions—but collapsed in the face of another.
In the helium story, Kuhn showed that a physicist and a chemist could have very different—but equally valid—views of the same phenomenon. Here, he applies that concept across time. Some knowledge from old paradigms still has great use, as exemplified by the fact that scientists still rely on Newtonian physics (principles that are hundreds of years old) and even certain elements of paradigms that are considered outdated.
As an example, Kuhn explains that some people believe Newton’s laws can be derived from Einstein’s. However, Kuhn notes that Einstein has a different view of “the fundamental structural elements” of the universe. In other words, to derive Newton’s law from Einstein’s work, one must change the meaning of at least one of the men’s works. Additionally, to even try to link the two is a luxury of hindsight and disregards what actually happened in the years between the theories.
For the first time in his treatise, Kuhn suggests that the linear history of science textbooks is not an accident but an active distortion. In order to legitimize the current scientific paradigm, science educators rewrite the history of science to make their own arbitrary work seem inevitable or objectively true.
Paradigms differ in the substantive ways they describe the universe. But each paradigm also entails a new set of methods, technologies, and problems—an acceptable solution in one paradigm is likely not acceptable in another. Kuhn then argues that paradigms are not only incompatible but incommensurable with one another.
“Incommensurability” is the idea that the very evidence that might prove a paradigm to its believers would seem completely irrelevant to people who disagree with the paradigm. Kuhn’s focus on incommensurability thus points to the difficulty of even articulating a paradigm to someone outside of it, much less convincing them of its correctness.
To demonstrate the differences between paradigms (and to hint at the cyclical nature of science), Kuhn discusses the ancient Greek belief that physical objects had innate natures. This idea had been popularized by Aristotle, but by the 1700s, Descartes’s idea of moving bodies (his “mechanico-corpuscular” view of nature) had taken its place. Many people viewed anything innate as “occult” and disreputable—until Newton published his Principia, which argued that gravity was an innate force. As the Principia became more widely used and respected, the ancient Greek view of innate properties came back into fashion.
Ancient Greeks believed that motion was innate, or built-in (as in, an object made of clay would fall quickly, because it came from the earth and so would return to the earth). Descartes mocked this theory, instead proclaiming that all motion was created by various particles in the universe bumping into one another (this is the “mechanico-corpuscular” theory). But because gravity (a relatively modern idea) is an innate force, existing in objects independent of their relationship to other objects, modern science is actually closer to Aristotle then to Descartes. This arc exemplifies Kuhn’s circular view of science, because the way scientists think about the relationship between objects hasn’t progressed in a perfectly linear way.
The idea of gravity as innate then had repercussions across other fields. In electricity, it helped scientists think through conduction as a built-in property. In chemistry, it allowed Lavoisier to build experiments based on the innate attractions of various chemical particles.
Just as Kuhn’s own work reaches across disciplines, he notes the vast consequences of paradigm shifts across distinct fields of science. For instance, Newton’s discovery in physics impacted Lavoisier’s chemistry.
Importantly, Kuhn does not see any one paradigm as more legitimate than the others. For example, Cartesian scientists (those working in the paradigm established by Descartes) gave up looking for gravity because it did not make sense in the context of their guiding theory; ignoring gravity allowed them to make other valuable discoveries. And though Newton would make sense of gravity, centuries later, Einstein’s work with relativity would return to something more like that of “Newton’s predecessors than his successors.” This once again demonstrates the circular nature of scientific revolutions.
If science is circular and not linear, as Kuhn claims, then a new paradigm is not any more impressive or accurate than an old one. Just as Newton’s theory of gravity marked a return to an old idea, Einstein’s theory of relativity resembled long-gone scientific ideas more than it did contemporary ones. Again, Kuhn’s argument that each paradigm is both valid and flawed also chips away at the idea that there is one solid scientific truth.
However, this circularity poses a crucial problem. Each paradigm has its kinds of questions, with its own kind of acceptable solution, and each has different standards for what is valid and valuable. In a sense, then, each paradigm proves itself and so is self-contained. So, how can one paradigm ever triumph over the other? To answer this question, Kuhn suggests that in addition to being constitutive of science, paradigms “are constitutive of nature as well.”
If each paradigm focuses only on the facts that support it, then it would seem impossible to ever disprove any one paradigm. In order to explain how paradigm shifts are eventually achieved, then, Kuhn turns his attention from paradigms as a thought experiment and instead focuses on paradigms as a lived experience for the scientists who work in them. This is what he means by paradigms being “constitutive of nature” as well as science—they reflect observable reality, not just abstract conjecture.