The Structure of Scientific Revolutions | Study Guide

Thomas Kuhn

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The Structure of Scientific Revolutions | Chapter 2 : The Route to Normal Science | Summary



Paradigms create the circumstances under which "normal science" proceeds. Kuhn defines normal science as research based on "past scientific achievements ... [the] scientific community acknowledges ... as supplying the foundation for its further practice." Paradigms range across diverse scientific subjects. Aristotle's Physics, for example, functioned as a paradigm for physics, while Ptolemy's Almagest served the same function for astronomy and Charles Lyell's Principles of Geology did so for geology. As Kuhn points out, these and other works defined the problems for their community's investigations, along with specific methods for field investigations. In this chapter Kuhn considers how paradigms are created to provide the model for normal science.

Without a paradigm "all ... facts that could ... pertain to the development of a given science ... seem equally relevant." Observations are made and facts are gathered, but there is nothing to steer or unify them into a coherent whole whereby provisional knowledge is achieved.

The groundwork for a paradigm consists of two features. First, its "unprecedented" achievements "attract an enduring group of adherents away from competing modes of scientific activity." Second, it defines problems for these practitioners to solve. Kuhn details these two characteristics in terms of "accepted examples of actual scientific practices," which include theory, law, application, and instrumentation.

The paradigm becomes known, for example, as "Ptolemaic astronomy" or "Newtonian wave optics." A student of the paradigm inherits the accepted norms of "the particular scientific community with which he will later practice." In this way a tradition is formed that shapes the culture of the community and a consensus is developed on the requirements for membership and practice. Moreover, paradigm "acquisition," along with "the more esoteric type of research it permits is a sign of maturity in the development of any given scientific field."

A paradigm emerges from its competitors partly because it is seen as the best explanation for the phenomena studied. Kuhn points out, however, this does not guarantee it will explain all of the relevant facts. There is still a field of research to be conducted. Moreover, as the paradigm gains strength from its number of adherents, rival theories fade away. In this way the paradigm becomes a discipline, or, perhaps a profession. Subsequently, professional bodies, scholarly journals, and other relevant organizations are formed, all of which are dedicated to paradigmatic work. The result is a community of specialists whose work is completed with other specialists in that community.


While Kuhn does not explicitly define "paradigm," he does explain a number of its properties. These include its metaphysical principles, fundamental laws and theoretical assumptions, standards for applying its laws and methodologies, the instruments and techniques for using them, and criteria for suitable scientific explanations.

Kuhn provides an example that helps the reader understand how a paradigm establishes scientific investigation in a particular community. Thinkers such as Planck and Einstein introduced the notion "light is photons." This characterization, along with its technical mathematical details, defines the ensuing research, which clarifies the concept. However, the characterization is different from the one derived from early-19th-century writings. Prior to this period, Newton's Optics "taught that light was material corpuscles." The shift from one paradigm to the next is, according to Kuhn, a scientific revolution.

As Kuhn points out, "No period between ... antiquity and ... the 17th century exhibited a single ... accepted view ... of light." Instead, many different theories existed. Consequently, new thought had to be developed from scratch. In Kuhn's estimation paradigms are essential to scientific activity, for "no natural history can be interpreted in the absence of ... some implicit body of ... theoretical and methodological belief." For Kuhn, without a paradigm, the physical sciences are simply an exercise in fact-gathering and form the basis for a very large set of encyclopedias.

Of course, no investigation begins without a set of assumptions. So, while a collection of facts gathered without a paradigm is in some sense random, an observer's beliefs about the world still orient his or her thinking. The reader can consider, for example, an observer following an Aristotelian tradition has a teleological belief about nature that an observer with a different worldview would not have.

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