 In 1961 Kuhn became a full professor at the University of California at Berkeley, having moved there in 1956 to take up a post in history of science, but in the philosophy department. This enabled him to develop his interest in the philosophy of science. At Berkeley Kuhn’s colleagues included Stanley Cavell, who introduced Kuhn to the works of Wittgenstein, and Paul Feyerabend. With Feyerabend Kuhn discussed a draft of The Structure of Scientific Revolutions which was published in 1962 in the series “International Encyclopedia of Unified Science”, edited by Otto Neurath and Rudolf Carnap. The central idea of this extraordinarily influential—and controversial—book is that the development of science is driven, in normal periods of science, by adherence to what Kuhn called a ‘paradigm’. The functions of a paradigm are to supply puzzles for scientists to solve and to provide the tools for their solution. A crisis in science arises when confidence is lost in the ability of the paradigm to solve particularly worrying puzzles called ‘anomalies’. Crisis is followed by a scientific revolution if the existing paradigm is superseded by a rival. Kuhn claimed that science guided by one paradigm would be ‘incommensurable’ with science developed under a different paradigm, by which is meant that there is no common measure for assessing the different scientific theories. This thesis of incommensurability, developed at the same time by Feyerabend, rules out certain kinds of comparison of the two theories and consequently rejects some traditional views of scientific development, such as the view that later science builds on the knowledge contained within earlier theories, or the view that later theories are closer approximations to the truth than earlier theories. Most of Kuhn’s subsequent work in philosophy was spent in articulating and developing the ideas in The Structure of Scientific Revolutions, although some of these, such as the thesis of incommensurability, underwent transformation in the process.