A paradigm shift is a phrase that was popularized by American physicist Thomas Kuhn to describe the nature of scientific revolutions, or fundamental changes in the basic concepts and experimental practices of a . Kuhn contrasts these shifts to the activity of normal science, which he characterized 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: παραδειγμα).