What are paradigms and why do they shift?

This paper provides a background to the concept of "paradigm" and "paradigm shift," based on Thomas Kuhn's description of scientific discourse communities in The Structure of Scientific Revolutions. Kuhn set out a model of scientific communication that included scientists primarily doing "normal science" based on a worldview - or paradigm - that has consensual agreement within the discourse community. When this paradigm fails to explain a number of new phenomena or concepts, however, Kuhn argues that science is in a time of crisis. To return the discourse community to a steady state, the crisis is often overcome by changing-or shifting-the paradigm.