The Structure of Scientific Revolutions | Study Guide

Thomas Kuhn

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The Structure of Scientific Revolutions | Postscript—1969 | Summary



Seven years after the publication of The Structure of Scientific Revolutions, Kuhn wrote a postscript in which he shares with his reader reflections on both the reception of the book, and further developments in his own thinking. He writes, "On fundamentals, my viewpoint is very nearly unchanged," but he also thinks the formulation of said viewpoint has generated problems. In order to address and resolve this, he plans to revise the work.

Kuhn then lays out what he believes the main problems to be, saying they "cluster about the concept of a paradigm." His goal is to disentangle them from "the notion of a scientific community." The sections that follow are organized around crystallizing both the concepts and their relations to each other. Additional criticisms Kuhn addresses in the postscript are charges of relativism and a confusion of the descriptive analysis of science with normative analysis.

1. Paradigms and Community Structure

In this section Kuhn seeks to break the "vicious circle" that defines paradigms in terms of communities and communities in terms of paradigms. He states a paradigm is what "members of a scientific community share, and ... a scientific community consists of men who share a paradigm."

Kuhn's proposed revision is to begin "with a discussion of the community structure of science," given its increasing interest to sociologists and historians of science. He provides a sketch of this discussion by identifying a scientific community in terms of their status as "practitioners of a scientific specialty." They share educational backgrounds, "have undergone similar educations and professional initiations," have joined similar professional organizations, and read similar "technical literature."

According to Kuhn, both normal science and revolutions are community-based activities. Consequently, understanding the former requires an understanding of the communities themselves. More specifically, it requires understanding how these communities change.

2. Paradigms as the Constellation of Group Commitments

Kuhn confesses the concept of a paradigm is not clearly articulated in the book. Indeed, according to a "sympathetic reader," there are "at least twenty-two different ways" the term paradigm is used. Kuhn settles on "disciplinary matrix" as a substitution for "paradigm."

Members of a scientific community share a "disciplinary matrix," allowing them to communicate ideas and make relatively unanimous scientific judgments. A disciplinary matrix is the common discipline in which practitioners investigate "ordered elements ... requiring further specification." It also reflects the shared beliefs in models of the discipline. Moreover, the disciplinary matrix reflects the values of the community. These values guide the method by which members of the community respond to a crisis. Lastly, Kuhn thinks of paradigms in terms of "exemplars," those "concrete problem-solutions that students encounter" in their education.

3. Paradigms as Shared Examples

Kuhn thinks of the shared example as "the central element of ... the most novel and least understood aspect of this book." The idea "scientific knowledge is embedded in theory and rules" erroneously localizes "the cognitive content of science," thereby leaving out the exemplars. Learning laws and theories without exemplars leaves the learner with "little empirical content." One can understand the form of a rule, but it is of little use without something to apply it to.

4. Tacit Knowledge and Intuition

Kuhn then turns his attention to the charge of relativism. More specifically, his critics believed he was "trying to make science rest on unanalyzable individual intuitions rather than on logic and law." That said, Kuhn does argue individuals "do in some sense live in different worlds." For example, the same stimulus can produce different sensations in two people. Members of a scientific community "learn to see the same things when confronted with the same stimuli" through the training process. Indeed, he points out, "An appropriately programmed perceptual mechanism has survival value," and goes on to say, "A group that could not tell wolves from dogs could not endure."

5. Exemplars, Incommensurability, and Revolutions

The charge of relativism is also leveled at Kuhn's claim paradigms, or exemplars, are incommensurable. Part of his response to this charge is a comparison between what happens when mathematicians disagree about the conclusion of a proof. In this case they "can retrace their steps one by one, checking each against prior stipulation." Unless the disagreement is about "the meaning or application of stipulated rules," it can be resolved by recourse to those rules. The problem for the community of scientists, however, is those very rules are scrutinized when they fail to resolve an anomaly. At this point persuasion enters in order to facilitate the rebuilding of consensus.

Moreover, Kuhn argues the communities from one paradigm to the next are incommensurable—they effectively speak different languages, which means they have fundamentally different understandings. It does not follow, however, they cannot communicate. Communication by analogy is surely a viable option. The process of translating from one "language" to the next can also prompt the sort of gestalt shift previously discussed.

Kuhn addresses the relativist charge head-on. On one hand, he does not think incommensurability commits him to the view scientific progress is not possible. On the other hand, he does not believe there is a "theory-independent way to reconstruct phrases like 'really there.'" The gap between knower and known—the real, in this case—is closed by a theory, and reopened when the theory is supplanted by another, which closes it for its practitioners.


Kuhn's primary reason for writing the postscript is to address the most vehement criticisms, some of which he thinks are based on misunderstandings he caused. Other criticisms he takes to be rooted in a misreading of the text. For example, he takes the criticism he confuses descriptive analysis with normative analysis to be a misreading of the text. He claims there is philosophical precedent for the view descriptions are inextricably value-laden.

It is worth noting Kuhn's postscript makes an effort to salvage two central meanings of "paradigm" articulated in the text. The first is paradigm "stands for the ... constellation of beliefs, values, techniques ... shared by the members of a ... community." It also denotes the "concrete puzzle-solutions which ... can replace explicit rules as a basis for the solution of ... remaining puzzles." The first sense is "sociological," while the second sense focuses on "exemplary past achievements."

As it pertains to the first meaning, Kuhn distinguishes the scientific community from its paradigm—communities can be discussed independently of their paradigm. At the same time, members of the community share a paradigm, and are distinguished as a community by the paradigm. The second meaning implies there are many scientific communities, and their structures change over time.

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