Paradigm Shift

The idea of the paradigm shift is Thomas Kuhn's account of how science actually changes over time, set out in The Structure of Scientific Revolutions, published in 1962 with an expanded second edition in 1970. Kuhn described most scientific activity as normal science, a period of puzzle solving carried out inside an accepted paradigm, a shared set of theories, methods and exemplary problem solutions that tells a scientific community what counts as a legitimate question and a legitimate answer. When observations turn up that the reigning paradigm cannot explain, these anomalies can accumulate into a crisis, and if a rival paradigm emerges that resolves the crisis, the field can undergo a scientific revolution in which the old paradigm is replaced rather than gradually extended. Kuhn's account differs sharply from Karl Popper's falsificationism: where Popper held that a single reliable failed prediction should lead to a theory's rejection, Kuhn observed that working scientists routinely treat anomalies as puzzles to be solved within the existing paradigm rather than as immediate grounds for abandoning it.