The Structure of Scientific Revolutions

by

Thomas S. Kuhn

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The Structure of Scientific Revolutions: Chapter 7 Summary & Analysis

Summary
Analysis
Kuhn points out that even as anomalies are constructive—leading to new discoveries and theories—they are also destructive of the knowledge that has come before. Moreover, just as anomalies are able to alert scientists to new kinds of phenomena, the scientific “crises” these anomalies cause usually lead to new theories. “Failure of existing rules,” Kuhn explains, “is the prelude to a search for new ones.”
Anomalies do lead to new ideas and discoveries. But, bolstering Kuhn’s claim that science is far from linear, anomalies also destroy much of the research and experimentation that has been done in the last paradigm. Therefore, science is neither linear nor cumulative (as textbooks say it is).
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To illustrate his point, Kuhn turns to astronomy. Ptolemy, an ancient Greek, had come up with a mostly reliable system for predicting the movements of planets and stars, in which he placed Earth at the center of the solar system. In fact, Ptolemy’s view was so successful that some engineers still use it today. But as more and more people used Ptolemy’s calculations, more and more discrepancies arose, and various scholars began to believe that “no system so cumbersome and inaccurate […] could possibly be true of nature.” This growing awareness prompted Copernicus to develop a model of the solar system with the sun at the center.
In Copernicus’ time, the Catholic Church was focused on trying to create an accurate calendar to properly honor Christ’s birth, death and resurrection. The Ptolemaic paradigm, though it had been accurate for centuries, was no longer sufficient. Copernicus’ discovery—one of the most radical and important in the history of science—therefore came directly out of the crisis caused by the increasingly “cumbersome and inaccurate” calendar process.
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As with Copernicus, Lavoisier’s discovery of oxygen came out of a crisis—and as with Copernicus, many scientists thinking about oxygen in the 1770s struggled with competing applications of their supposedly shared paradigm. In fact, Kuhn sees the “proliferation of versions of a theory” as one of the key signs of a scientific crisis. And as Lavoisier and his contemporaries tried to adapt the existing theory (which centered on the idea of combustible “phlogistons”), their work began to look more and more like the competing works of a pre-paradigm discipline.
In Lavoisier’s time, many people believed that there was a special substance called a “phlogiston” that was uniquely responsible for fire and combustion. However, different scientists applied this theory in such different ways that agreement became almost impossible—and so scientists could not collaborate or specialize as long as phlogiston theory persisted. Lavoisier’s exploration of oxygen allowed the field to return to some kind of workable consensus.
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Lastly, Kuhn cites an example from physics. As early as 1815, scientists were struggling to prove Isaac Newton’s ideas that light is merely mechanical wave motion. But rather than paying attention to this anomaly, scientists ignored the experiments and tried to theorize new edits to the original paradigm. It was nearly a century before James Maxwell, a committed Newtonian, started to think about magnetism—thereby throwing Newton’s theory into crisis and allowing Einstein, a few years later, to pioneer the theory of relativity.
Kuhn has previously mentioned that paradigms perpetuate themselves by ignoring all of the facts that do not support them. The century that elapsed before Maxwell was able to fully question Newton’s ideas testifies to the strength of paradigms and normal science, which—if they are compelling enough—are able to preserve a scientific status quo for decades.
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Kuhn notes several similarities between these three examples: one, it usually only took 20 or 30 years for a new paradigm to emerge out of crisis. Two, scientists recognized problems in the paradigm long before a full-on crisis emerged. And finally, other people or observations predicted the new paradigm but were ignored. In fact, the most famous foreshadowing of a discovery came from Aristarchus, an ancient Greek philosopher who argued (like Copernicus) that the sun was at the center of the universe—centuries before Copernicus was even born. 
Several times throughout his book, Kuhn shows how science often repeats itself. No example is clearer than that of Aristarchus, who had the exact same vision of the universe as Copernicus did, only thousands of years earlier. Copernicus’ rediscovery of Aristarchus’ work (which he probably had not read) exemplifies this cyclical pattern.
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