The Structure of Scientific Revolutions

by

Thomas S. Kuhn

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The Structure of Scientific Revolutions: Chapter 6 Summary & Analysis

Summary
Analysis
When people think of science, they are usually picturing normal science: it is cumulative, linear and very successful at finding answers. But how does normal science, which avoids novelty, end up producing scientific revolutions? In other words, Kuhn wants to investigate how discoveries “produced inadvertently by a game played under one set of rules” are able to illuminate another set of rules entirely.
Earlier, Kuhn articulated that scientific progress is cyclical (from normal science to crisis and then back again). Here, he argues that this cycle happens for a reason—crisis cannot happen without the traditionalism (and fear of novelty) inherent in normal science. It is only by operating under a certain “set of rules” that new ways of thinking can emerge.   
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Kuhn argues that a paradigm shift begins with an “anomaly”: some case or instance in which the rules of the paradigm appear fundamentally at odds with nature. Scientists then explore that anomaly and create new basic assumptions with which to explain this unexpected fact. And finally, the paradigm shift ends when the “anomalous has become the expected.”
Paradigms, with their rules and predictions, teach scientists what to expect. When something does not go according to expectation, then, normal scientists notice—and so anomalies are easier to spot the more established a paradigm is. Kuhn defines the process of a paradigm shift as noticing an anomaly and changing assumptions and rules to explain that anomaly. The paradigm shift is over when the anomaly becomes accepted rather than novel.
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In turning their attention to the anomaly, scientists are also blurring the lines between factual and theoretical discovery. To illustrate this, Kuhn cites the history of oxygen science. In the 1770s, many different scientists were trying to understand oxygen; some were trying to isolate one gas from the other gases in the air, while others (like Lavoisier) were making sense of oxygen in terms of atoms and chemical energy. Real discovery, then, takes time, because it involves “recognizing both that something is and what it is.”
In his exploration of the discovery of oxygen, Kuhn further complicates the simple, linear textbook narrative of science. Though scientists might notice an anomaly, it is not always clear whether that anomaly is an issue of theory or of fact. Making sense of an anomaly requires both noticing that the anomaly exists in the first place (“that something is”) and uncovering what that anomaly means in the context of a paradigm (“what it is). No discovery is ever as straightforward (or as individualized) as textbook history makes it out to be.
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Lavoisier’s discovery of oxygen initiated a paradigm shift. But Kuhn is careful to point out that Lavoisier had long been skeptical of the scientific knowledge he had been taught. Once Lavoisier started to notice an anomaly, his discovery of oxygen gave “shape and form” to the new paradigm that would allow him to depart from the received one. Many of Lavoisier’s contemporaries, however, could never understand his work because they remained convinced of the old paradigm.
Again, Kuhn draws readers’ attention to the human side of scientific progress. Though Lavoisier is heralded for his crucial contributions to chemistry, Kuhn is interested in the doubt and uncertainty (the personal and professional crisis) that spurred his work. Moreover, Kuhn makes it clear that while paradigm shifts can be dramatic, they often happen slowly over time.
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The invention of X-ray machines also exemplifies this kind of discovery from anomalies. Wilhelm Roentgen, testing cathode rays, saw light glowing in an unexpected part of his apparatus. This surprise pushed him to develop the X-ray, which then opened entirely new doors in science. But again, other people had seen that strange glow before Roentgen did—and had ignored it, because it was incompatible with their accepted paradigm’s beliefs.
If Roentgen wasn’t highly educated and trained, he would not have known to be surprised by something as seemingly insignificant as a strange glow. Kuhn suggests that it’s because Roentgen was so well-versed in normal scientific practice that he was able to notice even the slightest anomaly. This is how normal science makes crisis—and new discovery—possible.
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The discovery of X-rays was not immediately greeted with applause; instead, many people were shocked and angered by such a radically new idea. Worse still, apparatuses that had been viewed in one way now had to be seen in another way, and so past scientific work was discounted and confused. Kuhn uses this example to argue that to use a given machine with a particular lens carries “an assumption that only certain types of circumstances will arise.” These assumptions are necessary for normal science to proceed—and at the same time, the disruption of these assumptions is what  allows for whole new ways of understanding the world.
Kuhn uses this X-ray anecdote to explore the idea that scientific technology, which is designed to meet the needs of a paradigm, must either transform in its usage or lose relevance as paradigms shift. In other words, even machines (which are, of course, neutral) are not purely objective and unbiased, because people use them under the “assumption that only certain types of circumstances will arise.” In other words, scientific apparatuses can’t be separated from human biases.
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A final example of anomalous discovery is the Leyden jar (a major experiment in the field of electricity). Though efforts to create this jar were guided by the fluid theory of electricity popular in the 1700s, in the process of actually making the apparatus, scientists discovered the much more useful principle of electrical conduction.
Many scientists in the 17th and 18th centuries believed that electricity was an invisible fluid. As they tried to create a jar to capture this fluid, however, they realized instead that electricity is conducted (transferred) through certain substances like lead. This is an example of an anomalous discovery that led to a paradigm shift.
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Kuhn then draws on a psychological experiment to argue that the longer someone pays attention to an anomaly, the more they are forced to acknowledge and make sense of it. In the experiment, people were shown some normal cards and some odd ones (like a black 4 of hearts). At first, participants assumed the anomalous cards were normal, but by the end of the experiment, they were rethinking the entire structure of a deck of cards.
Kuhn’s multi-disciplinary interests again become evident here, as he turns his focus to psychology. In doing so, Kuhn also reminds readers that scientists, too, have personal psychologies—they share all humans’ tendency to ignore the unexpected until the anomalous becomes so evident and undeniable that it reshapes expectations. 
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Finally, Kuhn argues that developed—specific—paradigms allow more easily for this kind of resistance. Only when scientists are looking for very miniscule, precise things (the very things dictated by the developed paradigm) can they notice that those things are behaving in unexpected ways. Therefore, the more rigid a scientific paradigm becomes, the easier it is for scientists to spot an anomaly. This is why scientific revolutions always come out of normal science.
As the X-ray story demonstrated, the rigidity of normal science is what allows for new ideas to emerge. This is one of Kuhn’s central paradoxes: though normal science tries to prevent original thought, its strict boundaries are the very thing that ultimately cause the paradigm to collapse. 
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