Context
The Structure of Scientific Revolutions (1962) is written from a historian's perspective and Kuhn touches on a wide variety of historical events.
The author had already written a book called The Copernican Revolution (1957). Mediaeval Europe’s astronomy was Ptolemaic and stated that the sun and planets orbited Earth. But Ptolemy could see that simple orbits could not account for the movements of Mars, Jupiter and Saturn, and proposed they moved in “epicycles”, orbiting a point that was itself orbiting Earth. Astronomers devised complicated systems to account for the anomalies in their observations. This is presented by Kuhn as the traditional response, instead of searching for a different basic paradigm. Copernicus's theory offered a new paradigm: the earth and the planets moved around the sun, not vice versa. However, his theory was incomplete since it assumed orbits were perfectly circular. Kuhn offers this as an example of science's imperfection. Another Kuhnian idea of scientific revolutions is the slow spread of a new paradigm, as in Tycho Brahe's proposal of a hybrid of Earth and sun-centred models.
In Principia Mathematica (1687), Isaac Newton suggested the force of gravity “would be the same for all types of matter at all positions in the universe”. Newton sought laws that would apply at all times and in all places. He created a “revolution” out of the contradictory views on the nature of light. Kuhn calls it “the first nearly uniformly accepted paradigm for physical optics”.
But it would be a century before anyone made equipment capable of measuring this constant. Meanwhile, many astronomers found the moon’s movements refused to conform to Newton’s laws. As Kuhn describes it: “some… suggested replacing the inverse square law with a law that deviated from it at small distances." He noted that this simply defined a new puzzle and did not solve the old one. Scientists clung to Newton's theory until they managed to make the moon fit it.
In 1778 Antoine Lavoisier was the first to realise that things burn by incorporating a gas that is part air – something he named “oxygen”. However, Lavoisier didn’t get it quite right: he thought that oxygen was an atomic “principle of acidity” that formed a gas only when combined with “caloric”, a hypothetical fluid thought to be responsible for heat. Yet his insight into combustion trumped the old theory and opened the way to a new world of chemical research.
Kuhn's interpretation is:
“Discovering a new sort of phenomenon is necessarily a complex event, one which involves recognising both that something is and what it is.”
From Darwin, Kuhn drew one conclusion: that all scientists should learn one of the lessons of the Darwinian revolution: progress doesn’t have to have a goal. He states:
“All the well-known pre-Darwinian evolutionary theories… had taken evolution to be a goal-directed process. The ‘idea’ of man and… contemporary flora and fauna was thought to have been present from the first creation of life, perhaps in the mind of God…. For many… the abolition of that teleological kind of evolution was the most significant and least palatable of Darwin’s suggestions. 'The Origin of Species' recognised no goal set either by God or nature…. What could ‘evolution,’ ‘development,’ and ‘progress’ mean in the absence of a specified goal?”
Kuhn understood science as an exercise in solving puzzles. When scientists find phenomena that contradict the dominant paradigm inherent in science, they try hard to make these anomalies fit the norm. Before Albert Einstein’s special theory of relativity (1905), the prevailing view was that space was filled with an invisible substance, “ether”, through which light travelled. No one had ever managed to detect it and traditional science had been forced to provide many ingenious explanations of this failure.
When Einstein provided an alternative to the ether theory Kuhn saw it as a paradigmatic change:
“Within the new paradigm, old terms, concepts, and experiments fall into new relationships. To make the transition to Einstein’s universe, the whole conceptual web whose strands are space, time, matter, force, and so on, had to be shifted and laid down again on nature as a whole.”
The rise of Gestalt psychology, focusing on the inconsistency of perception, also influenced Kuhn’s thinking. He referred to Gestalt psychology to capture the idea that a paradigm structures individual perceptions of the world. Kuhn enlarged this ‘Gestalt switch’ to the scale of nations, societies and cultures, which resulted in a change of behaviour and policies. This is his large ‘paradigm shift’, as for example in a fundamental change in scientific theory. This comes about, not through crucial experiments, but through the accumulation of anomalies until the advocates of an old paradigm die out and leave the field to practitioners of a new paradigm.
Commentary
In the introduction to The Structure of Scientific Revolutions (1962), Kuhn explains his radically new conception of scientific discovery. Most people believe that scientists make linear progress toward objective truth. Kuhn believes that the history of science is more circular than linear and that by teaching people to look at the history of science in this way, he can help reshape the popular view of what science is and what it can accomplish. He argues that the study of the natural world develops through a perpetual cycle of scientific revolutions, in which one set of questions and perceptions is replaced by a different set of scientific beliefs.
Kuhn then describes what he calls the process of normal science, which is what takes place once one transformative insight or discovery has created a new “paradigm,” or a collection of perceptions, rules and strategies that define a certain scientific era. In normal science, scientists learn about these rules and strategies through textbooks and then work to apply them to a variety of problems.
The author argues that normal science, followed by the majority of scientists, actively discourages new and original thinking. Instead, the goal of normal science is an“... attempt to force nature into […] the box that the paradigm supplies.”
This means that normal science entails working to prove and specify a given theory, not to alter it. This is useful because it allows scientists to focus on a specific set of problems and build on one another’s work instead of constantly arguing with one another.
Nonetheless, sometimes in the course of normal science, someone notices an anomaly that the theory fails to explain. As more and more people start to pick up on this irregularity, an intellectual crisis breaks out. Various researchers try to defend the existing theory in different ways, and the scientific community starts to disagree. Eventually, Kuhn suggests, one brilliant thinker has an intuitive revelation—and a new scientific theory, able to explain the anomaly, is born. Over time, this person’s theory persuades more and more scientists, and a new paradigm takes hold. This process through which one paradigm replaces another is what he calls a scientific revolution. He cites as one example Copernicus’s 1543 realisation that Earth rotates around the sun, which replaced centuries of belief in a geocentric universe. Another example is Antoine Lavoisier, whose work in chemistry suggested that combustion was not an intrinsic property of certain chemicals but rather the result of different compounds reacting with one another.
Kuhn then draws several conclusions about the nature of scientific revolutions. First, he maintains that normal science, though it discourages new discovery, is ultimately what makes scientific revolutions possible. In order to notice an anomaly, scientists need to know what specific things to expect, and that is exactly what normal science teaches them to do.
Kuhn also observes that each new paradigm tries to destroy and replace the old one rather than build on it. This is why Kuhn views scientific progress as circular rather than linear. For example, Aristotle believed that objects had innate natures that caused them to move in certain ways. René Descartes questioned Aristotle’s theory, believing that all motion was the result of various substances bumping into one another. Most people then dismissed Aristotle’s conception, until Isaac Newton theorised gravity as an innate property, putting his followers more in line with Aristotle than with Descartes. Rather than moving in a straight line, therefore, science had moved in something like a circle.
Kuhn adds that no one scientific theory or paradigm is inherently more accurate or better than another. Rather, because each theory is the product of the arbitrary perceptions and questions defined by its moments in time, a paradigm shift is fundamentally a change in the way scientists see and experience the world. That is why one worldview or paradigm is almost impossible to square with another (what he calls “incommensurability”). Moreover, the author emphasises that scientists are human and that new paradigms emerge, not because they have more inherent worth, but because they are more persuasive.
The author also argues that because science is circular, subjective, and based on perception, it will never reach one single, objective truth. In fact, he suggests that no such objective truth exists.
In his postscript to his original text, written seven years later, Kuhn responds to critics and clarifies some of his earlier points. Specifically, he emphasises that while his theory does have some general applications, science is a unique field because there is more professional training and less room for disagreement or creativity than in other disciplines. Finally, he calls for more study of various kinds of intellectual communities, as these are the groups that produce most collective knowledge.
Themes
Linear Progress vs. Circular History
Textbooks tend to present the history of science as a linear story of progress. Thomas Kuhn, a historian who first trained as a physicist, argues the opposite: he suggests that each great scientific discovery ushers in a new way of looking at the world (what he terms a paradigm), which then prompts a new set of scientific questions and techniques. Rather than building on the last paradigm, each new paradigm completely upends the last. Then, the new paradigm undergoes the same cycle of invention, problem-solving, crisis, and collapse. In viewing the history of science as cyclical rather than linear, Kuhn argues that science is more dependent on historical context than textbooks make it seem. This is in part because scientists themselves are invested in presenting their work as objective and correct rather than as one of many possible ways of tackling a problem.
Textbooks present Albert Einstein’s physics as a direct descendant of Isaac Newton’s. Kuhn, however, feels that Newton and Einstein are actually operating under two completely different paradigms. Though the two men used some of the same terms (“space,” “time,” and “mass,” for instance), those words meant very different things to them, and to force Einstein’s worldview onto Newton’s earlier research is to distort the true meaning of his work. Kuhn therefore sees this insistence on linear history as harmful: by disguising these changes, he argues:
“... the textbook tendency to make the development of science linear hides a process that lies at the heart of the most significant episodes of scientific development.”
Kuhn believes that new paradigms and the new beliefs and experiences that accompany them, are the most essential part of understanding how scientific research grows and changes. To suggest that each scientist is thinking along the same lines as his predecessors is to erase the messy, more human reality of how science develops in favour of a deceptively neat narrative. Kuhn further argues that, like the textbooks they learn from, scientists also tell a linear, but inaccurate, version of their field’s history. Rather than acknowledging that each paradigm has particular values and viewpoints, scientists erase past perceptions by labelling them errors or mistakes. Kuhn’s project is to show how each view is different but equally valid.
Though scientists try to validate their own paradigm by erasing the ones that have come before, Kuhn insists that a true historian of science must always acknowledge the radical differences between various paradigms of scientific thought. He argues that scientists are particularly likely to rewrite history in their favour, in part because science, which positions itself as objective and grounded fully in the natural world, seems to exist independently from historical context. Because scientists are able to prove their ideas through experiments and because their work so often has real-world applications, it seems unnecessary to introduce any historical complexity or doubt into their research. But Kuhn makes clear that while he sees scientific discoveries as operating within a cycle,
“... that circularity does not at all invalidate them. But it does make them parts of a theory and, by doing so, subjects them to the same scrutiny regularly applied to theories in other fields.”
In other words, by acknowledging that their field is cyclical and dependent on context, scientists are forced to think more critically about their work. Moreover, Kuhn’s view of scientific history allows each paradigm’s questions and findings to remain useful even after the paradigm itself has been abandoned, thereby expanding what counts as scientific knowledge.
Perception and Truth
Though scientists’ work relies on collecting empirical data, Kuhn argues that scientists’ views of the world also play an important role, because their perceptions are what dictate which questions they ask and what they focus on in their research or experiments. As Kuhn sees it, each radically new scientific discovery heralds a new way of perceiving the world, a new paradigm. But while Kuhn emphasises that these paradigms are a useful way to solve problems, he also makes clear that a new paradigm is more like a fundamental shift in perception than an accumulation of knowledge that brings scientists closer to the truth. Kuhn concludes that while scientists may find new ways of looking at new kinds of problems, they will never get closer to an objective truth, which he believes does not exist.
Crucially to his argument Kuhn shows how perception and belief are necessary in order to make any scientific work possible. Kuhn suggests that
“... the operations and measurements that a scientist undertakes in the laboratory are not ‘the given’ of experience but rather ‘the collected with difficulty.’”
In other words, even to make basic decisions about what to write down from their experiments, scientists must make a great many decisions about what is important or useful. Kuhn argues that there is so much sensory information in the world that approaching it as a truly neutral observer is impossible. Instead, even when scientists believe they are being completely objective, they are in fact choosing to focus their attention on some data points at the expense of others. Crucially, Kuhn then emphasises how that choice is guided by internal beliefs and values. Rather than depicting science as a collection of objective observations and experiments, Kuhn notes that
“... an apparently arbitrary element, compounded of personal and historical accident, is always a formative ingredient of the beliefs espoused by a given scientific community at a given time.”
This means that in order to decide what kind of questions to ask and techniques to use, scientists must draw on the “personal and historical” context of what is important to them. To illustrate his point, Kuhn draws on the metaphor of a Rorschach test in which there is a piece of paper with an ambiguous drawing on it. The horizontal drawing initially looks like a bird, but when the paper is flipped 90 degrees, it then appears to be an antelope. Similarly, when scientists draw on their innate, initial perceptions, they are looking at the world from a certain angle, and so their problems and solutions seem almost inevitable. (Neuroscientist Anil Seth describes an experiment in visual illusions that concludes that whether you see circles or rectangles depends on your culture.)
Kuhn makes it clear that scientific engagement with the universe is always perceptual, so when scientific perception shifts, he argues the universe itself becomes “different.” In emphasising that paradigms are about shifts in perception, Kuhn is also careful to clarify that no one paradigm is better or more truthful than another. On comparing Galilei’s view of the pendulum with the prevailing one of Aristotle, when the Italian discovered that pendulum swings take the same time, no matter their size, Kuhn argues that the conclusions depended on different approaches. Aristotle had taken a qualitative and verbal approach; Galileo developed a quantitative and mathematical approach.
Kuhn asks:
“Why did that shift of vision occur? Through Galileo’s individual genius, of course. But note that genius does not here manifest itself in more accurate or objective observation of the swinging body. Descriptively, the Aristotelian perception is just as accurate.”
Though each paradigm involves a different set of perceptions, Kuhn is firm that one is not “more accurate or objective” than the other. Both merely involve different ways of looking at the exact same thing, and because it is impossible for humans to understand anything without looking at it, it is impossible to get a completely neutral observer who could declare whether Galileo’s view is better or worse than Aristotle’s.
Kuhn suggests that all science can offer is new paradigms of perception, not any objective truth. In one of the book’s most famous quotations, Kuhn blurs the line between myth and science:
“... if these out-of-date beliefs are to be called myths, then myths can be produced by the same sorts of methods and held for the same sorts of reasons that now lead to scientific knowledge. If, on the other hand, they are to be called science, then science has included bodies of belief quite incompatible with the ones we hold today.”
Indeed, because all scientific language draws on particular points of focus or underlying beliefs, Kuhn believes that “language thus restricted to reporting a world fully known in advance can produce mere neutral and objective reports on ‘the given.’” In short, no one can look at a pendulum swinging and view it without any lens or beliefs. And because no individual scientist can separate their particular view from what is actually happening, no scientific community will ever be able to articulate what is actually happening.
Normal Science vs. Extraordinary Science
Kuhn suggests that there are two different kinds of science: extraordinary science, in which one individual suddenly conceptualises the world in a new light, and normal science, which involves trying to “force nature” to conform to their expectations. Extraordinary science leads to new sets of questions and techniques, while normal science involves answering those questions and applying those techniques. Yet rather than dismissing normal science, Kuhn makes a case for its importance: because it eventually forces scientists to face the holes in their beliefs. Normal science is what makes extraordinary science possible.
Kuhn argues that day-to-day, normal science, is not about new ideas and discoveries and in fact, normal science actively works to suppress this kind of original thinking. Instead, Kuhn refers to normal science as “mop-up work,” in which scientists apply the rules of their paradigm to a variety of increasingly specific problems, cleaning up the existing ideas without adding any of their own. To illustrate his point, Kuhn compares normal science to a “jigsaw puzzle.” Completing a jigsaw puzzle is not about imagining a different or more interesting picture, rather it is about putting together the pieces to form the picture on the puzzle box. Similarly, Kuhn argues that normal science is about providing new examples of familiar conclusions through experimental data and research. But to continue this kind of puzzle-solving work, normal science must not acknowledge any new guiding rules or concepts. As Kuhn puts it, normal science often suppresses fundamental novelties because those innovations undermine the basic ideas of the current paradigm. For the “mop-up work” of normal science to have meaning, the ideas and beliefs that undergird that science must not be changed. For scientists who conduct research and experiments according to the rules of a given paradigm, then, thinking outside the box would actually invalidate the vast majority of their daily work.
Extraordinary science, which does involve radically new ideas, has almost nothing to do with the everyday practices of science, such as research and calculation. If Kuhn used the predictable jigsaw puzzle to symbolise normal science, he saw extraordinary science as an unsolved puzzle: scientists then often speak of the flash that enlightens a previously obscure puzzle. Importantly, he describes the process of extraordinary science with language more often reserved for discussing moments of artistic inspiration. If normal science is like solving a jigsaw puzzle, extraordinary science is about creating a new picture entirely. And while normal science involves preserving the world as it is, extraordinary science marks such a change in perception that it is a “transformation of the world within which scientific work was done.” Because extraordinary science reorients scientists’ perspective on the world, it also changes their own personal experiences and perceptions.
However, though normal science and extraordinary science are very different, Kuhn shows that neither type would be possible without the other. Extraordinary science, the inventor of new paradigms, always opens the door to normal science. As Kuhn describes it:
“... during the period that the paradigm is successful, the profession will have solved problems that its members could scarcely have imagined and would never have undertaken without commitment to the paradigm.”
Extraordinary science, which provides a set of scientific values and beliefs, is necessary for normal scientists to focus on a small set of questions and to build on one another’s work. However, because normal science allows scientists to see the flaws of their paradigm, it also highlights the anomalies any new theorist must consider. For example, X-ray technology was discovered when Wilhelm Conrad Röntgen, conducting a routine experiment with cathode rays, noticed a glow where he did not expect to see one. Because normal science teaches its practitioners what to look for with great detail and precision, it is much easier to notice the unexpected and therefore to realise the flaws in a paradigm that lead to the revelation of an entirely new paradigm. This is why scientific theories are also formed with what Kuhn calls a “certain circularity.” Extraordinary science makes normal science possible and in turn, normal science, by slowly identifying irregularities in the current paradigm, creates the need for extraordinary science. Even as Kuhn draws a distinction between the two types of science, he does not suggest that either one is better than the other; in fact, he suggests that they are both necessary parts of scientific discovery.
Intuition and Emotion
Science is usually thought of as an objective discipline based on observation, facts, and hard data. Yet Kuhn argues that science is far less logical than it seems. Kuhn believes that each world-altering scientific discovery, from the law of gravity to the theory of relativity, actually begins with intuition in which one scientist’s instincts lead them to experience the world in a new way. Moreover, in order for the scientific community to adopt this new theory, Kuhn suggests that they must be persuaded not by rational proof but by aesthetic or emotional appeals. The author refutes the idea that scientists are objective and emotionless and suggests that intuition and feeling are what allow one scientific idea to triumph over another.
Kuhn tries to understand the emotional motives behind what he calls normal science. Scientists are commonly thought to be motivated by
“the desire to be useful, the excitement of exploring new territory, the hope of finding order, and the drive to test established knowledge.”
Kuhn argues that, for the most part, a scientist’s day-to-day life is driven by a sense of competition: “if only he is skilful enough, he will succeed in solving a puzzle that no one before has solved or solved so well.” Kuhn goes on to comment that normal science requires someone who prioritises the thrill of solving puzzles and impressing colleagues above all else. Here, Kuhn completely undercuts the classic portrait of the objective, disinterested scientist and instead suggests that scientists are “thrill-seekers,” addicted to finding out the answers that elude their colleagues.
Kuhn also describes great, world-changing scientific discoveries as deeply personal and instinctive. For the lone geniuses who engage in extraordinary science,
“the new paradigm […] emerges all at once, sometimes in the middle of the night, in the mind of a man deeply immersed in crisis.”
Here he suggests a deep interest in the interior, spiritual lives of scientists. He asks readers to imagine these great thinkers in their private bedrooms in “the middle of the night,” not only confronted with a crisis of knowledge but actually immersed in it. Interestingly, while science is often understood to be observation-based, Kuhn moves his focus from these geniuses’ stimuli to their sensations:
“Very different stimuli can produce the same sensations..." and “the same stimulus can produce very different sensations.”
Kuhn’s claim is that scientists rely on lived experience (sensations) to make their conclusions and so understanding them as real people with real lives is crucial to understanding their work.
Kuhn goes further to argue that the triumph of one scientific idea over another is more about feeling than fact.
“The transfer of allegiance from paradigm to paradigm is a conversion experience that cannot be forced.”
Again, Kuhn thinks of science as something spiritual, almost a conversion, one that develops not through logic but through deeply personal realisations. Though these arguments might never be made directly, many scientific theories appeal directly to scientists’ sense of what is aesthetic, the new theory is said to be ‘neater,’ ‘more suitable’ or ‘simpler’ than the old. Theories do not triumph because they are “right” so much as because scientists admire their simplicity or their style. Here, Kuhn’s focus on scientists’ humanity goes to the heart of his argument that one idea is not more truthful than another, but rather that it appeals more to a given group of human beings in a given time. Kuhn also compares scientific revolutions to political ones: both rely on the techniques of mass persuasion, focusing less on logic and more on rhetoric and argumentation.
As Kuhn works to humanise individual scientists, he also is fascinated by scientists’ relationships with one another, both in terms of large-scale community and small-scale friendships or collaborations. He concludes that paradigm shifts can happen “not despite the fact that scientists are human but because they are.” Because scientists’ work is deeply personal, aesthetic, and experiential, they are able to move outside of the rigid bounds of logical problem solving and transform their field in the process.
Criticism of Kuhn's theory
One of the most influential examinations of Kuhn’s work took place at the International Colloquium in the Philosophy of Science, held at Bedford College, Regent’s Park, London, on July 11-17, 1965, with Karl Popper presiding. In that colloquium, John Watkins argued against normal science. Steven Toulmin asked whether the distinction between normal and revolutionary science holds water. Margaret Masterman pointed out that Kuhn’s use of “paradigm” was variable by showing more than twenty different usages.
L. Pearce Williams claimed that few, if any, scientists recorded in the history of science were "normal" scientists in Kuhn’s sense. He disagreed with Kuhn both about historical facts and about what is characteristic for science. Others then and since have argued that Kuhn was mistaken in claiming that two different paradigms are incompatible and incommensurable because, in order for things to be incompatible, they must be directly comparable or commensurable.
Popper himself admitted that Kuhn had caused him to notice the existence of normal science, but Popper regarded normal science as deplorable because, Popper claimed, it is unimaginative and plodding. He pointed out that Kuhn’s theory of science growing through revolutions fits only some sciences because some other sciences have in fact been cumulative—a point made by numerous other critics of Kuhn. In addition, Popper claimed that Kuhn really does have a logic of scientific discovery: The logic of historical relativism. He and others pointed out that in claiming that a new paradigm is incommensurable and incompatible with an older one Kuhn was mistaken because, Popper claimed,
“a critical comparison of the competing theories, of the competing frameworks, is always possible."
Popper sometimes called this the "myth of the framework." He continued,
“In science (and only in science) can we say that we have made genuine progress: That we know more than we did before.”
In The Structure of Scientific Theories, ed. with a critical Introduction by Frederick Suppe, Kuhn published an essay entitled “Second Thoughts on Paradigms” in which he admitted that his use of that term had been too plastic and indefinite and had caused confusion, and he proposed replacing it with “disciplinary matrix.” In an “Afterward” to the 1977 Second Edition of this work, Suppe claimed that there had been a waning of the influence of what he dubbed the Weltanschauungen (worldviews) views of science such as that of Kuhn.
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