In this blog post, we will compare the theories of Karl Popper and Thomas Kuhn—two leading philosophers who have examined the process of scientific knowledge development—and explore how Kuhn’s theory of scientific revolutions explains the actual process of scientific knowledge development.
Few would disagree with the assertion that advances in science and technology shape our future. Most people today believe that without such advancements, they would not enjoy the same quality of life they do now, and they recognize that science and technology are essential for securing a competitive edge against other nations. In other words, it is often taken for granted that scientific knowledge possesses a special value in and of itself and is superior to other disciplines. But is scientific knowledge truly that special compared to other disciplines?
This issue was also a major point of contention in 20th-century philosophy of science. While many philosophers agreed that science is a special discipline, they offered differing views on the source of that specialness. The core of this debate centered on explaining how scientific knowledge develops, with Karl Popper’s falsificationism and Thomas Kuhn’s theory of scientific revolutions serving as representative theories. In this article, I will compare these two theories and examine the significance of Kuhn’s theory of scientific revolutions.
First, let’s briefly examine Popper’s argument. Popper broke away from the inductivism of earlier logical positivists and defined the criterion of scientific knowledge as falsifiability. In other words, a scientific theory must always be open to the possibility of being proven wrong, and the greater its falsifiability, the better the scientific theory. From this perspective, he argued that scientific knowledge gradually approaches the truth through countless refutations and falsifications, and that science progresses as the theories that survive this process accumulate.
However, some philosophers subsequently began to argue that, rather than explaining scientific activity through a single logical rule or ideal, one must examine how actual scientists conduct their research.
Thomas Kuhn is the leading figure representing this perspective. His book, The Structure of Scientific Revolutions’, is regarded as a work that significantly overturned the traditional view of scientific knowledge. Kuhn differed from Popper in two major respects: one was his view on the objectivity of observation, and the other was his assessment of “normal science.”
Philosophers of science prior to Kuhn, including Popper, rarely questioned the premise that observation is an objective and rational activity. Popper himself stated that he supported common-sense realism and viewed objective observational facts as the basis for falsifying a theory.
In contrast, Kuhn argued that observation might not be as objective as commonly assumed. He contended that even when observing the same phenomenon, the way it is interpreted can vary depending on which theory one accepts. At the time, this was regarded as a highly innovative claim.
A hypothetical dialogue between Kepler and Tycho Brahe is often cited as a representative example to illustrate this point. The example illustrates that even if both men observed the same phenomenon, Tycho Brahe, who adhered to the geocentric model, would have said, “The sun is rising,” while Kepler, who accepted the heliocentric model, would have interpreted it as, “The Earth is rotating.” Another well-known example is that when looking at the same image, one person might perceive a panda’s face, while another might see the structure of a water molecule.
As such, even when observing the same object, differences in interpretation arise. In other words, observational results are not always objective, and observations are always influenced by the observer’s background knowledge and theories. From this perspective, observation cannot serve as absolute grounds for falsification, and Popper’s theory has certain limitations. In contrast, Kuhn persuasively explained the subjective nature of observation by analyzing actual cases from the history of science and the research processes of scientists. Furthermore, his insight is still highly regarded today because he revealed that the very criteria for interpreting observational results can change over time.
So, what does this background knowledge mean? To explain this, Kuhn introduced the concept of a “paradigm.” In a broad sense, a paradigm is a concept that encompasses the theories, values, research methods, and problem-solving approaches shared by the scientific community.
Scientists conduct research under a single paradigm during a specific period, which Kuhn termed “normal science.” He explained that when the existing paradigm can no longer solve problems, a scientific revolution occurs, leading to a shift to a new paradigm. In other words, scientific knowledge does not develop simply through the accumulation of existing knowledge but rather through a transition to a new system of knowledge at specific points in time.
Kuhn believed that normal science accounts for the majority of the time in the history of science and plays a crucial role in scientific progress. In contrast, he explained that revolutions are extremely rare events.
In contrast, Popper, while not completely denying the existence of normal science, viewed it as a factor that actually hinders scientific progress. He argued that when a counterexample is discovered, the existing theory must be immediately discarded and replaced with a new one.
However, when examining actual cases in the history of science, it is far more common for scientists to continue conducting research within the framework of normal science. This aligns more closely with Kuhn’s explanation.
Let’s look at a representative example. From the late 18th century to the early 19th century, Newton’s mechanics was accepted as the most powerful theory for explaining natural phenomena. However, the orbit of Uranus observed by astronomers showed significant discrepancies with the results calculated using Newton’s laws. According to Popper’s argument, Newton’s theory should have been discarded the moment this counterexample was discovered.
However, scientists did not act that way. They did not abandon Newton’s theory itself, nor did they conclude that Newton’s laws were wrong. Instead, while retaining Newton’s theory, they proposed a new hypothesis: they assumed that an as-yet-undiscovered planet existed beyond Uranus, exerting a gravitational influence. Subsequent calculations matched actual observations, and eventually, a new planet—Neptune—was discovered.
Most scientists do not immediately abandon a theory they trust simply because a counterexample has emerged. In fact, even Newton was aware, when he published ‘Principia’ in 1687, that there were phenomena his mechanics could not fully explain. If Newton had discarded his theory every time he encountered an unexplained case, it is highly likely that physics would not have advanced to its current level.
Newton’s theory was long accepted within the framework of normal science, and scientists resolved unexplained problems one by one, operating under the premise that Newton’s laws were fundamentally correct. Through this process, scientific knowledge continued to advance.
Thus, we can confirm that the actual process of scientific development includes a phase known as “normal science,” during which scientists solve problems within a established research framework. Kuhn explained that scientists during the period of normal science are engrossed in “puzzle-solving.” In other words, this means that scientists conduct research to solve specific problems while assuming that fundamental answers already exist.
Furthermore, normal science serves as an essential foundation for the advancement of engineering. If, as Popper’s ideal suggests, revolutionary changes occurred very frequently and existing theories were constantly replaced, engineering—which applies scientific knowledge for practical purposes—would struggle to establish a stable foundation. Engineers do not create new theories; rather, they develop actual technologies and products based on scientific knowledge trusted by the scientific community. Therefore, without normal science, engineering would also find it difficult to achieve sustained development.
Taking these points into consideration, it can be argued that Kuhn’s theory provides a more realistic explanation of how actual scientific research is conducted than Popper’s theory.
Even normal science, which appears so solid, eventually faces a crisis. When the existing paradigm can no longer adequately explain new problems, a scientific revolution occurs, leading to a shift to a new paradigm.
Kuhn argued that a scientific revolution does not occur simply because a large number of cases that do not fit the paradigm have accumulated. As phenomena that cannot be explained by the existing paradigm continue to pile up, scientists gradually begin to feel a psychological crisis. However, this crisis alone does not trigger a revolution. According to Kuhn, a scientific revolution occurs only when a new alternative emerges that can overcome the limitations of the existing paradigm.
He also argued that it cannot be assumed that a new paradigm is absolutely more advanced than the existing one, and that the two paradigms are in a relationship where they are difficult to reconcile.
This argument aligns to some extent with general human behavior. For example, when an unexpected crisis arises, people tend to first seek realistic alternatives to solve the problem rather than immediately abandoning their existing ways of acting. In most cases, people only adopt new behaviors after a sufficiently viable alternative has been established. This psychological characteristic of humans can be seen as aligning well with the process by which scientists during a scientific revolution adopt a new paradigm.
Summarizing the discussion so far, Kuhn provided a highly persuasive explanation of how scientific knowledge has actually evolved, and as a result, he is regarded as a figure who transformed the course of the philosophy of science. Unlike the leading philosophers of science of his time, who were scholars with degrees in philosophy, Kuhn was a scientist who majored in physics and earned a Ph.D. in the field. This background played a significant role in his ability to present a new perspective on the development of science.
Through his research in physics, Kuhn directly observed how scientific knowledge actually develops, and based on this experience, he conducted an in-depth analysis of cases from the history of science. As a result, he was able to provide a more accurate account of how actual scientists conduct research than the idealized models of scientific progress being discussed in the philosophical community at the time.
In contrast, established philosophers of science, including Popper, tended to focus on how science should progress. Kuhn, however, distinguished himself by analyzing how science has actually progressed through historical examples. For this reason, some philosophers at the time criticized Kuhn for lacking an understanding of philosophy.
However, today it is more widely accepted that Kuhn’s work marked a new turning point in the philosophy of science. He moved beyond the existing approach of explaining science solely through formal logic and presented a new perspective that emphasized the need to consider both the research methods of the scientific community and the historical processes of change. In particular, his significance is immense in that he expanded the understanding of scientific development beyond a simple “logic of discovery” to a perspective known as the “psychology of research,” which encompasses the actual process of research and the ways scientists think.
Even today, Kuhn’s concepts of paradigms and scientific revolutions are widely applied not only in the philosophy of science but also in various fields such as history, sociology, education, and business administration. Of course, it is difficult to view his theory as a perfect explanation of all scientific development processes, but it is hard to deny that it provided important insights into understanding that science is not merely a process of accumulating facts, but rather one that changes in the context of different eras, communities, and the emergence of new perspectives. If one seeks a more multidimensional understanding of the development of scientific knowledge, Kuhn’s theory of scientific revolutions—alongside Popper’s falsificationism—is an important theory that is certainly worth examining.
