This blog post compares the theories of two giants of philosophy of science, Karl Popper and Thomas Kuhn, examining what science is and how its nature can be explained.
Textbooks are the fundamental resource countless students rely on for their studies. For learning purposes, textbooks must contain only correct information, accompanied by thorough explanations. People naturally accept this content as truth. This characteristic is particularly pronounced in mathematics and science textbooks. Since textbook content teaches scientific facts established by countless mathematicians and scientists in the past, we perceive and learn them as self-evident truths.
However, before these facts were accepted as truth, humanity did not understand the principles governing the workings of the world. Simply put, much of what is written in science textbooks was merely one hypothesis among many, not truth, even just a few hundred years ago. Before these hypotheses gained acceptance as facts, countless scientists underwent the process of verifying and proving them, ultimately completing various theories that explain the world. We can examine the research they conducted through the history of science and understand how theories evolved.
Several philosophers of science have proposed different theories about how science progresses and what science essentially is. Among them, the most widely known are Karl Popper and Thomas Kuhn. While both theories explain what we call science and how it has changed over time, they hold distinctly different views. Popper expressed a critical perspective on Kuhn’s work during a symposium held by the International Society for the Philosophy of Science in 1965. So, which of these two claims offers the more accurate explanation? This article aims to discuss how each claim explains science and how science should be explained.
First, let’s examine Popper’s theory. The most fundamental term Popper uses to describe science is ‘falsifiability’. Let’s understand what this means by looking at some common examples.
– It will rain in the future.
– Crows are black.
Suppose we have these two propositions. Both can hold meaning for a positivist and are based on verifiability. For the first proposition, we simply need to observe rain falling in the future. For the second, we need to find a crow and confirm it is black. However, the first proposition holds no meaning according to Popper’s view. The reason is that we cannot falsify the first proposition. A proposition that cannot be falsified provides us with no useful information and therefore holds no meaning. The second proposition is falsifiable. We simply need to find a crow that is not black. If a white crow is discovered, the proposition can be revised and further developed.
As outlined above, Popper’s argument is that the criterion for distinguishing science from non-science should be set as falsifiability. Popper stated, “It is logically impossible to infer theories from empirically verified singular statements. Therefore, theories are never empirically verifiable,” arguing that the dividing line should be falsifiability, not verifiability.
Furthermore, Popper asserted that methodological determination in science is inevitable. Here, methodological rules are regarded as conventions and described as the rules of the game of empirical science. Moreover, the supreme rule governing methodological rules is that other rules of scientific procedure must be designed in such a way that they do not prevent any statement in science from being falsified. Positivists were skeptical of methodology, disliking the idea that meaningful problems could exist outside the realm of empirical science. However, Popper argued that methodology is necessary because if everything outside natural science problems were meaningless, then debates about the concept of meaning would also prove meaningless.
Now let us examine Kuhn’s theory. Kuhn refers to the formation and change of scientific theories as ‘normal science’. Normal science denotes research activities firmly grounded in one or more past scientific achievements. These scientific achievements are termed paradigms. When the scientific community accepts a paradigm that enables their theories and research, they enter the normal science phase. This normal science shares characteristics with puzzle-solving. That is, within the normal science phase, established rules exist, and problems are solved within those rules, much like solving a puzzle. This continues until problems arise that cannot be solved within the existing paradigm. At that point, new paradigms, different from the old one, emerge. Among these new paradigms, the ones that survive overthrow the old paradigm and become accepted. Kuhn refers to this process as a revolution.
The old and new paradigms mentioned earlier share the property of incommensurability. Incommensurability means that during a revolution or paradigm shift, new concepts or claims cannot be strictly compared with old concepts or claims. The shift in concepts about celestial bodies from the geocentric model to the heliocentric model serves as a prime example. The geocentric and heliocentric models existed as distinct paradigms. The transition from geocentric to heliocentric cannot be described as building upon the geocentric model; rather, it involved dismantling the existing theory and constructing the heliocentric model anew.
Even a brief explanation of what Popper and Kuhn each argued reveals how vastly different their perspectives on science are. Kuhn focused on how scientific theories are accepted and changed by people, while Popper placed greater emphasis on whether a theory has scientific meaning. Because their points of focus differ, a clear comparison or judgment of right and wrong may be impossible. However, since both philosophers address the question of ‘what science is’, we can discuss this aspect.
First, let’s examine the falsifiability Popper discusses. Popper argues that science requires statements to be testable; propositions that cannot be falsified are unscientific. The raven proposition presented earlier illustrates this well. But what about cases where scientists cannot falsify something through experience? The first thing that comes to mind relates to thought experiments. A thought experiment, as the name suggests, involves conducting an experiment in the mind. We cannot directly verify whether the propositions related to the experiment’s outcome are true. In other words, we can say such propositions are empirically unfalsifiable. Galileo’s thought experiment on inertia derived propositions explaining facts already proven correct in theories like the law of inertia and the law of conservation of energy. Since we cannot replicate this precisely in a laboratory setting, empirical falsification is effectively impossible. The debate between Bohr and Einstein regarding the Copenhagen interpretation of quantum mechanics follows a similar logic. Here, the experiment Einstein proposed to refute the interpretation was also a thought experiment. In this case, it was an experiment even more difficult to implement than Galileo’s thought experiment—practically impossible. Therefore, it cannot be performed empirically and cannot be falsified (similarly, one must conduct a thought experiment to refute it, and indeed, Bohr did so). Nevertheless, no one would claim that the debate between the two was unscientific. Of course, since most scientific theories possess falsifiability, Popper’s claim cannot be said to be wrong.
So what about Kuhn’s normal science? In the case of the thought experiment presented earlier, according to Kuhn’s theory, it could be treated as a single paradigm. If the paradigm created by Galileo can be explained as having triumphed over the existing paradigm to establish itself as a theory, then no error occurs. So, can Kuhn’s theory be said to be more correct? That would not be the case. To discuss this, let us return to the field of quantum mechanics. The theory of quantum mechanics can be seen as emerging because the existing paradigm, Newtonian mechanics, failed to function properly in the microscopic world. Quantum mechanics was judged to be the correct theory and became normal science. According to Kuhn’s theory, the paradigm of quantum mechanics triumphed over the paradigm of Newtonian mechanics, thereby establishing a new normal science in its place. However, we do not claim that Newtonian mechanics is a completely incorrect theory; physics in the macroscopic world is still explained by Newtonian mechanics. In other words, the two theories coexist within the field of physics. While it is true that the concepts of quantum mechanics revolutionized our understanding of the microscopic world, it cannot be said that it has entirely replaced the existing paradigm.
According to the logic presented earlier, we cannot say which of the two theories is correct. As the examples mentioned show, there are scientific events difficult to explain using either theory, making it challenging to explain the entirety of science. A theory that perfectly explains science must apply well to all fields within science. However, the fields of science are extremely diverse, and the cases that emerge in each field are all different in nature, making it very difficult to explain everything with a single theory. In fact, it is said that contemporary philosophers of science focus more on meta-discourse about individual sciences rather than on discussions about science in general. Therefore, there will likely be an appropriate theory of the philosophy of science for each scientific field, and Popper’s theory or Kuhn’s theory could be one of them.
To propose an example based on the earlier illustration: the developmental process of science related to thought experiments can be explained by Popper’s theory of normal science, while the advancement in quantum mechanics can be described as a process of refining theories through continuous falsification. Science cannot be explained by a single theory alone.
Although the theories proposed by Popper and Kuhn are currently the most widely known and best explain science, it is clear they cannot account for all phenomena. It is also true that each theory can effectively explain phenomena within its specific domain. Therefore, I argue that to fully explain science, we must not rely on a single theory but rather appropriately combine multiple theories that can effectively explain numerous situations.
