Thomas Kuhn and Karl Popper are considered two major figures of the philosophy of science in the 20th century. Several ideas of Kuhn and Popper made it into the realm of the mainstream culture and now are amid those few concepts from the field of philosophy of science that are known to some extent by the contemporary practicing scientists. Kuhn is known for his concept of paradigm shift to describe those quite rare situations within the history of science when one field gives up its framework in favor of some other framework. This comes as an outcome of a crisis which is induced by a growing number of puzzles which are impossible to resolve within the initial framework. As for Popper, he has introduced the idea of falsifiability as a manner in which genuine theories of science should be distinguished from pseudo-science. This paper compares the views of Kuhn and Popper on how science works. Just as Kuhn’s views on Popper and other critics, expressed in his article, “Reflections on My Critics” (1970), were structured along three major categories, method, normal science, and irrationality, this essay will compare and contrast Kuhn and Popper’s views with regard to these categories.
“Normal” Science
The flashpoint for the differences between views on the philosophy of science of Kuhn and Popper was their stance on criticism and growth of knowledge. While Kuhn stressed the importance of the so-called “normal” science, which developed through puzzle solving, his opponent questioned the idea of “normal” science, construed like this, as good science at all. Kuhn’s fundamental idea was that science would not get anywhere if scientists were busy attacking what they had found, instead of accepting as well as refining it. Popper, in contrast, emphasized significance of striving to overthrow scientific theories that could, for all their authors and users were aware of, be false (Popper, 2002).

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For Kuhn, the existence of “normal” science comes as a logical corollary of the occurrence of revolutions. He claims that “the central episodes in scientific advance… are revolutions” (1970, p. 241). The value of “normal” science is clear for Kuhn. That is why he thinks that once the “normal” science is adopted, there is no longer need for criticism or theory proliferation. Kuhn sees benefits at focusing on just one theory. He explains this as follows: “Because they can ordinarily take current theory for granted, exploiting rather than criticizing it, the practitioners of mature sciences are freed to explore nature to an esoteric depth and detail otherwise unimaginable” (Kuhn, 1970, p. 247). It is here that the views of Kuhn and Popper drastically diverge.

Although Popper, too, recognizes the existence of “normal” science, he is an advocate of criticism and critical method of science. For Popper, critical attitude is at the center of a scientific persona and scientific progress and criticism is the most distinctive feature of the scientific method. He explained this as follows:

[I]t is the most characteristic feature of the scientific method that scientists will do everything they can in order to criticize and test the theory in question. Criticizing and testing go hand in hand: the theory is criticized from very many different standpoints in order to bring out those points which may be vulnerable … (Popper, 1940, p. 104)

In this way, for Popper, “normal” science was not proper science in Kuhn’s interpretation of this term. He distinguished science by a possibility of refutation using both observation as well as experiment. Here another difference becomes evident: Kuhn asserts that puzzle solving is fundamental to science, whereas Popper gives more credit to testing or applied science.

Difference in Perception of Normative and Descriptive Methods
Although both Kuhn and Popper are interested in the issue of how scientists should behave, they have different answers to this question. Kuhn in his writings does two things: gives a methodological prescription and provides a description of science. For him, these two things go together. Popper, unlike Kuhn, sees them as coming apart (2002, p. 28). For Popper, the goal of the science is getting closer to the truth, which means that science could possibly be unsuccessful to a large extent as it will fail to get nearer to that truth. In this way, Popper treats the normative question of how to behave as essentially separate from the question of how they do in reality behave.

Out of this difference, another significant difference between the two philosophers arises: Kuhn sees the normative issues through the lens of description whereas Popper through the lens of logics. Kuhn believes that science description “must, in the final analysis, be psychological or sociological” (Kuhn, 1970, p. 21) whereas Popper asserts that critical method is principal for science, because he believes that scientists’ search for truth requires, if to think logically, to get rid of falsehoods.

Kuhn and Popper differ in their views on rationality. Whereas both agree that science should be rational, they developed different understandings of rationality. For Popper it is critical attitude that defines rationality, while Kuhn believes that science need not be rational all the time. The ground for choosing a theory from other theories is the criteria of accuracy, fruitfulness, scope, and simplicity (i.e. choosing is quite irrational). Thus, for Kuhn science is irrational.

In summary, Kuhn and Popper’s views on the nature of scientific method and on the essence of science greatly diverged. At the same time, today it would unwise to reject either of these approaches, since they are rather complimentary than contradictory. Both lead to a holistic understanding of science and how it works.
of science and how it works.

  • Kuhn, T.S. (1970). Logic of discovery or psychology of research?, in I. Lakatos and A. Musgrave (Eds.), Criticism and the Growth of Knowledge (pp.1-24). Cambridge: Cambridge University Press.
  • Kuhn, T.S. (1970). “Reflections on my critics,” in I. Lakatos and A. Musgrave (Eds.), Criticism and the growth of knowledge (pp.231-278). Cambridge: Cambridge University Press.
  • Popper, K.R. (2002) The logic of scientific discovery. Psychology Press.
  • Popper, K.R. (1970). “Normal Science and its dangers‟, in I. Lakatos and A. Musgrave (Eds.), Criticism and the Growth of Knowledge (pp.51-58). Cambridge: Cambridge University Press.
  • Popper, K.R. (1940). What is dialectic? Mind, 49, 402-436.