In the academic year 1971–1972, Kuhn was granted a new leave of absence from Princeton University[aut]Princeton University and began the spring term of 1972 at the IAS. In April 1972, he received a formal invitation from the IAS’s director, Carl Kaysen[aut]Kaysen, Carl, to become a member of the School of Social Science for the next five years. Kuhn, of course, accepted. He could not have foreseen that the School, and Kaysen in particular, would become the target of serious criticism and controversy from a group of natural scientists by the end of that year, and that in early 1973 he would be asked to take a stand for or against Kaysen. I shall return to this point in a further section below. For the moment, it is important to remark that this problem did not seem as important for Kuhn as the development of his own work on the history of quantum physics. In turn, the latter was not as significant for him, especially from 1975 onwards, as his return to Structure. By the time he left Princeton and also the IAS, where he had spent a term per year for the last seven years, for the MIT in 1979, he was devoted full-time to his old problems in the philosophy of science, though from the new vistas that his recent work had opened for him. I shall talk about all this in the next pages.