---
title: "The Structure of Scientific Revolutions"
chunk: 5/9
source: "https://en.wikipedia.org/wiki/The_Structure_of_Scientific_Revolutions"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T04:37:26.249284+00:00"
instance: "kb-cron"
---

=== Incommensurability ===
According to Kuhn, the scientific paradigms preceding and succeeding a paradigm shift are so different that their theories are incommensurable—the new paradigm cannot be proven or disproven by the rules of the old paradigm, and vice versa. A later interpretation by Kuhn of "commensurable" versus "incommensurable" was as a distinction between "languages", namely, that statements in commensurable languages were translatable fully from one to the other, while in incommensurable languages, strict translation is not possible. The paradigm shift does not merely involve the revision or transformation of an individual theory, it changes the way terminology is defined, how the scientists in that field view their subject, and, perhaps most significantly, what questions are regarded as valid, and what rules are used to determine the truth of a particular theory. The new theories were not, as the scientists had previously thought, just extensions of old theories, but were instead completely new world views.
Such incommensurability exists not just before and after a paradigm shift, but in the periods in between conflicting paradigms. It is simply not possible, according to Kuhn, to construct an impartial language that can be used to perform a neutral comparison between conflicting paradigms, because the very terms used are integral to the respective paradigms, and therefore have different connotations in each paradigm. The advocates of mutually exclusive paradigms are in a difficult position: "Though each may hope to convert the other to his way of seeing science and its problems, neither may hope to prove his case. The competition between paradigms is not the sort of battle that can be resolved by proofs." Scientists subscribing to different paradigms end up talking past one another.
Kuhn states that the probabilistic tools used by verificationists are inherently inadequate for the task of deciding between conflicting theories, since they belong to the very paradigms they seek to compare. Similarly, observations that are intended to falsify a statement will fall under one of the paradigms they are supposed to help compare, and will therefore also be inadequate for the task. According to Kuhn, the concept of falsifiability is unhelpful for understanding why and how science has developed as it has. In the practice of science, scientists will only consider the possibility that a theory has been falsified if an alternative theory is available that they judge credible. If there is not, scientists will continue to adhere to the established conceptual framework. If a paradigm shift has occurred, the textbooks will be rewritten to state that the previous theory has been falsified.
Kuhn further developed his ideas regarding incommensurability in the 1980s and 1990s. In his unpublished manuscript The Plurality of Worlds, Kuhn introduces the theory of kind concepts: sets of interrelated concepts that are characteristic of a time period in a science and differ in structure from the modern analogous kind concepts. These different structures imply different "taxonomies" of things and processes, and this difference in taxonomies constitutes incommensurability. This theory is strongly naturalistic and draws on developmental psychology to "found a quasi-transcendental theory of experience and of reality."

=== Exemplar ===
Kuhn introduced the concept of an exemplar in a postscript to the second edition of The Structure of Scientific Revolutions (1970). He noted that he was substituting the term "exemplars" for "paradigm", meaning the problems and solutions that students of a subject learn from the beginning of their education. For example, physicists might have as exemplars the inclined plane, Kepler's laws of planetary motion, or instruments like the calorimeter.
According to Kuhn, scientific practice alternates between periods of normal science and revolutionary science. During periods of normalcy, scientists tend to subscribe to a large body of interconnecting knowledge, methods, and assumptions which make up the reigning paradigm (see paradigm shift). Normal science presents a series of problems that are solved as scientists explore their field. The solutions to some of these problems become well known and are the exemplars of the field.
Those who study a scientific discipline are expected to know its exemplars. There is no fixed set of exemplars, but for a physicist today it would probably include the harmonic oscillator from mechanics and the hydrogen atom from quantum mechanics.

== Kuhn on scientific progress ==
The first edition of The Structure of Scientific Revolutions ended with a chapter titled "Progress through Revolutions", in which Kuhn spelled out his views on the nature of scientific progress. Since he considered problem solving (or "puzzle solving") to be a central element of science, Kuhn saw that for a new candidate paradigm to be accepted by a scientific community,