Themes
Key
LitCharts assigns a color and icon to each theme in The Structure of Scientific Revolutions, which you can use to track the themes throughout the work.
Linear Progress vs. Circular History
Perception and Truth
Intuition and Emotion
Community and Knowledge
Normal Science vs. Extraordinary Science
Summary
Analysis
To some extent, Kuhn argues, “when paradigms change, the world changes with them.” Though scientists are not literally transported to a new planet, they begin to understand the world in radically new ways. Again using the example of the Rorschach test, Kuhn suggests that each new scientific student’s perception of the world “is determined jointly by the environment and the particular normal-scientific tradition that the student has been trained to pursue.” When a paradigm shift occurs, therefore, part of the student’s world changes.
Paradigms tell scientists both where to look and how to make sense of what they notice. So, just as turning a drawing of a bird sideways reveals a completely different picture (an antelope), thinking in terms of a new paradigm ushers in a new world. Kuhn thus emphasizes another facet of scientists’ humanity here: their professional work impacts how they move through and experience daily life.
Themes
Using the field of gestalt psychology, Kuhn points out that once people have seen the world in a new light, it is almost impossible to revert to their old perceptions of it. However, bridging the gap between historical study and psychology presents an interesting problem for Kuhn’s own work; he feels his work on this junction is not yet complete.
Gestalt psychology was a relatively new field in the 1960s, when Kuhn was writing. A “gestalt” is a whole that cannot be separated into component parts; gestalt psychology argues that people cannot perceive facts or details without taking into account context and prior belief.
Themes
In particular, while subjects of psychological experiments are able to acknowledge that the shift in reality is really a shift in their perceptions, scientists tend not to do so. Or, as Kuhn puts it, “looking at the moon, the convert to Copernicanism does not say ‘I used to see a planet, but now I see a satellite.’ […] Instead, a convert to the new astronomy would say ‘I once took the moon to be […] a planet, but I was mistaken.’”
Once scientists start believing in a paradigm, they must reject what came before as false. After all, in order to feel any sort of certainty in any kind of worldview, scientists must blame themselves for error—not acknowledge that each conclusion is as arbitrary and subjective as the last. This is why Kuhn distinguishes between seeing two different things (“I used to see a planet, but now I see a satellite”) and mistaking one thing for another (“I once took the moon to be a planet, but I was mistaken”).
Themes
Kuhn also discusses the example of Uranus, a celestial body that was the subject of much debate among astronomers. Throughout the 1700s, many different people observed Uranus as a star, because they did not note its motion. When one scientist finally saw it move, he believed it to be a comet. After several months of unsuccessful efforts to assimilate Uranus into existing comet theory, scientists accepted that it was a planet. And suddenly, right after accepting Uranus as a minor planet, astronomers began to see minor planets and asteroids everywhere. Kuhn argues here that in changing their beliefs about Uranus, scientists looked up at the sky and noticed different things.
Here, Kuhn demonstrates that his claim that different paradigms make different worlds is anything but a metaphor. When scientists accepted that there could be minor planets, they dramatically changed how they looked at the sky—and so all of a sudden, the very same bright dots were named and treated in a whole new way. In simpler terms: once scientists believed the sky could filled with minor planets, all those minor planets suddenly appeared, and the sky itself changed for the scientists who studied it.
Themes
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The most dramatic example of this shift in perception occurred with Galileo. Aristotle explained the pendulum by saying that heavy objects naturally fall, and the object at the bottom of the pendulum is merely falling slowly (because its chain holds it back). Galileo, however, began to take in the pendulum as a “swinging body” that repeats the same motion over and over again. This new way of seeing the pendulum allowed Galileo to come up with many critical scientific ideas about weight, incline, and velocity.
Later in the book, Kuhn will note that although Aristotle and Galileo understood a pendulum’s movement differently, both were approaching it with detailed, methodical observation. The difference in Galileo’s perspective—and the various rules it helped him create—was all about his internal beliefs, yet it led to a shift in how the world understood a wide range of external phenomena.
Themes
Kuhn notes that Galileo’s “shift of vision” did occur in part because of “his individual genius.” But at the same time, Galileo was drawing on the work of earlier scientists, who had come up with something called “impetus theory.” His knowledge of impetus theory allowed Galileo to see the pendulum as something separate and specific, not just a “swinging stone.” It was a knowledge of impetus theory, then, that allowed Galileo to see the world differently and therefore to conceptualize the pendulum.
Impetus theory, which was gaining popularity in the century before Galileo worked, dictated that once a force (an “impetus”) sets an object in motion, the object continues in the direction of the force. Galileo’s exposure to this theory, which had developed and spread slowly, allowed him to see the pendulum in a new light. This is another instance in which anomalies accumulate and reveal themselves slowly.
Themes
But if Galileo had gleaned insight from impetus theory, which was compatible with an old paradigm, Kuhn believes that his new way of seeing was ultimately the result of a “lightning flash” change in perception. In other words, if normal science leads to a crisis, it can never itself lead to a new paradigm. Instead, new paradigms are only reached by these almost intuitive reassessments of the natural world.
On the one hand, anomalies often emerge gradually; on the other hand, new paradigms—these breakages in scientific progress—emerge in an instant. More important, though, is the extremely unscientific way that Kuhn describes these changes in perception. This “lightning flash” moment is not objective and careful but personal and inspired, more like a moment of artistic genius than anything else.
Themes
Kuhn then pauses to consider why this focus on a given scientist’s “immediate experience” is so necessary. For centuries, Western epistemology has argued that sensory experience is “fixed and neutral.” Kuhn acknowledges that he does not believe sensory experience is really so simple—but that he does not have an alternative explanation. So, while Kuhn is confident that scientists’ draw on their paradigm’s assumptions for even seemingly factual observations, he lacks a theory of perception to describe why this is the case. Kuhn thus hopes for a paradigm shift in both psychology and philosophy that would help him explain this non-fixed, non-neutral form of perception.
Western epistemology, or the study of knowledge itself, has often assumed that observation is inherently unbiased: for centuries before Kuhn’s writing, historians and philosophers of knowledge assumed that everyone took in their surroundings in the same way. In pointing out the flaws—or anomalies—in this epistemological paradigm, Kuhn’s own work aims to resolve a crisis with a thought revolution in history, just as Copernicus, Newton and Einstein all did in their respective disciplines.
Themes
Stepping back, Kuhn notes that “neither scientists nor laymen learn to see the world piecemeal or item by item.” For example, a child learning to call her mother “mama” is also learning about gender and family structures in general. Paradigms do not determine single facts or experiences, and so paradigm shifts affect many ideas and observations at once.
Kuhn is returning to the idea of the psychological gestalt, which states that people struggle to view individual objects or ideas removed from context—people see structures and systems rather than a “piecemeal” assortment of items. When one observation is altered by a paradigm shift, then, scientists will also have to shift their views of everything related to that observation.
Themes
Fascinatingly, then, science in a new paradigm involves many of same techniques, tools and terms as science in the old paradigm did. However, even when the same techniques and technologies are applied in a new paradigm, they are understood to reveal dramatically different information.
Earlier, Kuhn recounted how machines made to capture cathode rays later became X-ray machines. While the technology was the same, the use and meaning of such devices were completely different.
Themes
To exemplify this, Kuhn discusses the scientific revolution caused by John Dalton. For much of the 18th century, chemists worked under the paradigm of affinity theory, which dictated that certain substances dissolved in others because of an innate attraction. At the end of the century, some chemists began to realize that a select few chemical mixtures had fixed proportions of their various ingredients. But no coherent theory was created, and the discipline started to fracture (and appear more like pre-paradigm science).
Just as the Ptolemaic model became an impractical way of creating a calendar, affinity theory in chemistry was becoming more and more difficult to apply to everyday situations. In both cases, scientific communities began to fracture when faced with a reality that became harder and harder to fit into their paradigm’s “box.”
Themes
Dalton was ultimately the one who overturned affinity theory with his famous atomic theory. However, Dalton identified as a meteorologist—in his initial tests, he was not using affinity theory at all. Because he came from a different discipline, Dalton was able to craft the law of fixed proportion (all atoms will bond to one another in simple, whole-number ratios). At the same time, Dalton’s theory allowed him to claim that any time ingredients in a compound were not in this kind of ratio, the compound was not chemical.
There are two important things to note about this passage: first, as a meteorologist, Dalton was able to view chemistry outside of affinity theory (and instead to think about atomic theory, which states that all molecules are actually made out of various smaller component parts). Second, as soon as he created a paradigm, Dalton immediately made it self-perpetuating.
Themes
Though some chemists were deeply opposed to Dalton’s view, this new paradigm quickly proved more useful and efficient. Since even skilled scientists had been conducting their experiments with different goals and ideas (under a different paradigm), Dalton had very little evidence for his theory initially. Instead, that evidence came after—future scientists “beat nature into line,” and when they were done, “the percentage composition of well-known compounds was different. The data themselves had changed.”
The lack of evidence for Dalton’s theory (at least at first) testifies to the ways in which paradigm shifts are more about creation than observation. But also, perhaps more than any other moment in the book, this anecdote illustrates Kuhn’s point about the ways in which paradigms not only change science but change the very world that science is done in—a paradigm changes “the data themselves,” in that scientists observe nature with the goal of fitting their observations into the paradigm.
Themes
