Thomas Kuhn

Kuhn used paradigm shift for a change in the basic concepts, methods, and standards guiding a scientific field. In The Structure of Scientific Revolutions, published in 1962, he argued that such changes occur when a prevailing paradigm can no longer handle important anomalies.

Normal science is research conducted within an accepted paradigm, with scientists solving puzzles according to its established assumptions and methods. Kuhn contrasted this relatively stable work with periods of crisis and scientific revolution.

Kuhn challenged the idea that scientific knowledge grows only through the steady accumulation of facts. He argued that revolutions such as the transition from Ptolemaic to Copernican astronomy can also change the standards used to judge explanations.

Incommensurability means that rival paradigms may use different concepts, methods, and standards, leaving no completely neutral measure for comparing them. Kuhn did not mean that comparison was always impossible, but that it was more complicated than testing both theories by one permanent set of rules.