An example of a paradigm shift in theory ?

A paradigm shift, as identified by American physicist and philosopher Thomas Kuhn, is a fundamental change in the basic conceptsand experimental practices of a scientific discipline. Kuhn contrasted these shifts, which characterize a scientific revolution, to the activity of normal science, which he described as scientific work done within a prevailing framework (or paradigm). In this context, the word "paradigm" is used in its original meaning, as "example" (Greek:παράδειγμα).

The nature of scientific revolutions has been a question posed by modern philosophy sinceImmanuel Kant used the phrase in the preface to his Critique of Pure Reason (1781), referring to Greek mathematics and Newtonian physics. In the 20th century, new crises in the basic concepts of mathematics, physics, andbiology, revitalized interest in the question among scholars. It was against this active background that Kuhn published his work.

Kuhn presented his notion of a paradigm shift in his influential book The Structure of Scientific Revolutions (1962). As one commentator summarizes:

Kuhn acknowledges having used the term "paradigm" in two different meanings. In the first one, "paradigm" designates what the members of a certain scientific community have in common, that is to say, the whole of techniques, patents and values shared by the members of the community. In the second sense, the paradigm is a single element of a whole, say for instance Newton’s Principia, which, acting as a common model or an example... stands for the explicit rules and thus defines a coherent tradition of investigation. Thus the question is for Kuhn to investigate by means of the paradigm what makes possible the constitution of what he calls "normal science". That is to say, the science which can decide if a certain problem will be considered scientific or not. Normal science does not mean at all a science guided by a coherent system of rules, on the contrary, the rules can be derived from the paradigms, but the paradigms can guide the investigation also in the absence of rules. This is precisely the second meaning of the term "paradigm", which Kuhn considered the most new and profound, though it is in truth the oldest.[1]