Although Kuhn himself noted that he used the word “paradigm” in at least 23 different ways in the first edition of The Structure of Scientific Revolutions (1962), the core meaning is that a paradigm defines and prescribes how research is conducted in a science, and it also presents a picture of the world as studied by that science.

During normal science, all practitioners are expected to work within the reigning paradigm of their field and extend accepted theories to new circumstances. There is widespread agreement on one coherent world view in a mature science. In immature sciences, competing schools of thought have followers who defend the paradigm of the viewpoint they subscribe to. Paradigms are not absolutely true for all time and can be literally overthrown by the adoption of new paradigms.