It is worth taking stock of the various respects in which Kuhn’s epistemology of science is aptly called an evolutionary epistemology, for, as we saw earlier, the term “evolutionary epistemology” does not identify a single, well-defined approach to epistemology.

In Part i, I argue that Kuhn believes there are genuine revolutionary changes in science. But, throughout Part ii, I have argued that Kuhn’s epistemology is an evolutionary epistemology. One might think there is a tension in Kuhn’s epistemology of science with his characterization of science in both evolutionary and revolutionary terms. The question is: can Kuhn have it both ways? Can an epistemology of science be both an evolutionary epistemology and also acknowledge that there are revolutionary changes in science? In answering this question I aim to clarify what in Kuhn’s epistemology is aptly characterized as revolutionary and what is aptly characterized as evolutionary.

There is no better place to begin a study of Kuhn’s developed epistemology of science than with his remarks on scientific revolutions. This is so for three reasons. First, revolutions figure so importantly in Kuhn’s account of scientific change. It is their structure that he was trying to elucidate in The Structure of Scientific Revolutions. And it is their existence which supports his non-cumulative account of scientific knowledge. Second, revolutionary scientific changes were the focus of much of the criticism against Kuhn’s account of science. According to Kuhn, the development of scientific knowledge is punctuated by scientific revolutions, dramatic and unsettling events that undermine the traditional picture of the growth of scientific knowledge as cumulative. Such an account of science was widely perceived as posing a significant threat to the rationality of science. Third, in his later work Kuhn develops a new definition and understanding of scientific revolutions, one designed to avoid the pitfalls of his earlier characterization of scientific revolutions as paradigm changes.

In this chapter, I examine Kuhn’s developed account of scientific revolutions. He no longer identifies revolutions as paradigm changes. Rather, a revolution involves the replacement of an accepted scientific lexicon or taxonomy with a new one. Such changes are precipitated by crisis in the research community. And the resolution of the dispute between advocates of the competing theories or lexicons cannot be resolved by means of shared standards. Importantly, Kuhn regards the research community, or scientific specialty, as the locus of theory change and scientific change in general. Revolutions are not just changes in individual scientists’ beliefs. This helps us understand why Kuhn stopped comparing revolutionary changes to gestalt shifts. Research communities are incapable of experiencing gestalt shifts. Hence, a revolutionary change occurs only when a research community replaces the theory with which it works with another theory. This is one important respect in which Kuhn’s epistemology of science is aptly described as a social epistemology.

In The Structure of Scientific Revolutions Kuhn developed a novel and interesting account of the dynamics of scientific change, one that was deeply at odds with the assumptions that had previously informed the outlook of philosophers of science. To many of his readers it seemed that whenever Kuhn denied a widely accepted philosophical assumption about science, he offered a paradox in its place.

To begin with, Kuhn alleged that scientific knowledge was not cumulative. He is famous for drawing our attention to what has come to be called “Kuhn-loss,” the “knowledge” allegedly lost when one theory replaces another. Yet he adamantly insisted that there is scientific progress.

Kuhn’s evolutionary epistemology

Kuhn’s epistemology of science is an evolutionary epistemology. Critics and commentators alike have generally either ignored or misunderstood this dimension of his project. My aim in Part ii is to rectify this situation. I aim to show that understanding Kuhn’s evolutionary perspective on epistemology is the key to understanding his epistemology of science. Such a perspective, I argue, is at odds with the perspective most philosophers bring to their study of science. Kuhn’s approach to evolutionary epistemology requires a radical shift in perspective. Indeed, this is one reason why Kuhn is so frequently misunderstood.

So far, we have examined how Kuhn modified his understanding of scientific revolutions and paradigms and their roles in scientific inquiry and scientific change. Scientific revolutions and paradigms are two of the central concepts in Structure. A third key concept introduced in Structure concerned Kuhn throughout his career, namely incommensurability. Rather than trace the history of the use of this term, as we did with the concept of “paradigm,” my aim here is to distinguish the variety of ways in which Kuhn used the term “incommensurability.”

Kuhn regarded the notion of incommensurability as extremely important to understanding scientific change. In fact, in 1990, he claimed that his “own encounter with incommensurability was the first step on the road to Structure,” adding that “the notion still seems … the central innovation introduced in the book” (1993/2000, 228). Later in his career, Kuhn devoted more and more energy to the issue of incommensurability.

Right from the beginning, that is, from the publication of Structure, Kuhn’s epistemology of science was an evolutionary epistemology of sorts. What changed over time was the extent to which his epistemology was an evolutionary epistemology. Later in his life, the evolutionary dimensions of his epistemology were extended and developed. Scientific change, he came to believe, was even more like evolutionary change than he had initially thought.

Kuhn first compares scientific change to evolutionary change in the final pages of Structure. There, Kuhn (1962a/1996) challenges the common assumption that science is moving toward a fixed goal set by nature. Instead, he claims that science is like evolution, pushed from behind. Kuhn claims that this change in perspective, that is, seeing that science is not moving toward a goal fixed by nature in advance, is the key to understanding the nature and dynamics of scientific change.

One of the most striking forms of scientific change is the rapid and seemingly endless growth of new scientific specialties. Nicholas Rescher (1978) notes, for example, that the number of specialties in physics has grown from 19 in 1911, to 100 in 1954, and reaches 205 in 1970 (229, table 3). Philosophers of science seldom discuss this dimension of scientific change. Specialization has been neglected by philosophers, in part, because they have tended to emphasize the value of unification in science (see, for example, Friedman 1974; and Kitcher 1993). Unifying theories deepen our understanding of the natural world by revealing connections between otherwise disparate phenomena. Specialization seems antithetical to this goal. Specialization can and often does create barriers between scientists. Thus, for many philosophers, specialization is seen as either an impediment to developing unifying theories or a temporary resting state along the way to developing unifying theories.

In chapter 1, in the brief discussion of the discovery of x-rays, we saw that theory replacement is not the only response that a research community has when it encounters persistent anomalies. Sometimes, as Kuhn notes, anomalies are dealt with by creating a new scientific specialty, a new research community that has as its concern the study of the previously anomalous phenomena. Further, the creation of new specialties is by no means a temporary state in the development of science. Rather, as Kuhn claims, specialization often serves to advance our epistemic goals in science. Hence, philosophers need to develop a better understanding of the role and effects of specialization in science.

One of Kuhn’s key contributions to the philosophy of science was to direct our attention to the epistemic relevance of the social dimensions of scientific inquiry. Kuhn shows us that there are limits to what we can learn about science and scientific knowledge when we restrict ourselves to a study of the logic of science, as the logical positivists and Popper do. Scientific inquiry is a complex social activity. And the social dimensions of science play an important role in ensuring the success of science. Kuhn’s epistemology of science is thus a social epistemology of science. Kuhn, however, does not describe his project as a social epistemology of science. This is not surprising, given that the term “social epistemology” became widely used among philosophers only in the 1980s, with the publication of the journal Social Epistemology.

The term “social epistemology” has come to mean different things to different people. Sometimes it connotes the study of such things as expertise or testimony as sources of knowledge (see Schmitt 1994, 4–17; Goldman 1999, chapter 4). At other times, social epistemology concerns science policy issues, including whether and to what extent the public which pays for science through taxation should shape the scientific research agenda (see, for example, Fuller 1999). And “social epistemology” sometimes connotes a concern with whether the social characteristics of inquirers affect their prospects of developing an objective account of the world or some part of it (see Schmaus 2008). Kuhn’s epistemology of science is a social epistemology because he sought to understand how the social dimensions of science contribute to the success of science.

In the previous two chapters, I both explained and offered a defense of Kuhn’s developed account of theory change. According to Kuhn’s developed account, revolutionary theory changes are no longer characterized as paradigm changes. In light of Kuhn’s mature account of theory change, it is worth examining his mature view of paradigms. To do this, it will be worth examining how he came to discover the notion of a paradigm in the first place.

Kuhn tells two different stories about his discovery of the concept “paradigm.” In the Preface to Structure Kuhn claims to have discovered the notion of a paradigm while working at the Center for Advanced Studies in the Behavioral Sciences at Stanford in 1958/59. Interacting with many social scientists, Kuhn was struck by the differences between the natural sciences and the social sciences. In the former, there is broad agreement about the fundamentals of the field, whereas in the latter there is often significant disagreement about fundamentals. Kuhn claims that “attempting to discover the source of that difference led [him] to recognize the role in scientific research of what [he has] since called ‘paradigms’ ” (1962a/1996, x). Paradigms, as he explains, are “the universally recognized scientific achievements that … provide model problems and solutions to a community of practitioners” (x). Paradigms, Kuhn claims, are a standard feature of the natural sciences, but not of the social sciences.

Kuhn’s social epistemology

Sociologists of science are certainly correct to see the importance of the social dimensions of scientific inquiry in Kuhn’s work and the constructive role he attributes to such factors in aiding scientists in realizing their epistemic goals. In this respect, sociologists have been more sympathetic and careful readers of Kuhn’s work than philosophers. But, to many philosophers, sociologists of science have taken things too far. Their emphasis on the social dimensions of science leave one wondering what role rationality and evidence play in resolving disputes in science.

So where has the road that Kuhn traveled since the publication of Structure taken us?

One of my principal aims in this book has been to encourage a re-examination of Kuhn’s work. I believe that there are still important insights to gain from his work as we develop an epistemology of science. More precisely, I have argued that: (1) we need to move past the popular negative reading of Kuhn, and (2) in our efforts to understand his constructive contributions to philosophy of science we will benefit from attending to his later work, in particular, Kuhn’s mature notion of scientific revolutions and his emphasis on scientific specialization. For the most part, philosophers have seen Kuhn’s account of science as a threat to the rationality of science. Consequently, in their discussion of Kuhn’s work many philosophers have sought to show either how Kuhn is mistaken in his descriptive account of scientific change, or how he is mistaken about the normative implications of theory change in science. They have seldom sought positive insights from his work.