MSN's Encarta defines a paradigm shift as "a radical change in somebody's basic assumptions about or approach to something.". The term paradigm shift was used by Thomas Kuhn in his 1962 book The Structure of Scientific Revolutions. The Stanford Encyclopedia of Philosophy wrote the following regarding Kuhn's concept of the paradigm shift:
"A mature science, according to Kuhn, experiences alternating phases of normal science and revolutions. In normal science the key theories, instruments, values and metaphysical assumptions that comprise the disciplinary matrix are kept fixed, permitting the cumulative generation of puzzle-solutions, whereas in a scientific revolution the disciplinary matrix undergoes revision, in order to permit the solution of the more serious anomalous puzzles that disturbed the preceding period of normal science."