For reasons which will appear, the problem of the avant-garde, as presented by Professors Ackerman and Kubler, has caught my interest in unexpected and, I hope, fruitful ways. Nevertheless, both on grounds of competence and because of the nature of my assignment, my present remarks are directed primarily to Professor Hafner's rapprochement of science and art. As a former physicist now mainly engaged with the history of that science, I remember well my own discovery of the close and persistent parallels between the two enterprises I had been taught to regard as polar. A belated product of that discovery is the book on Scientific Revolutions to which my fellow contributors have referred. Discussing either developmental patterns or the nature of creative innovation in the sciences, it treats such topics as the role of competing schools and of incommensurable traditions, of changing standards of value, and of altered modes of perception. Topics like these have long been basic for the art historian but are minimally represented in writings on the history of science. Not surprisingly, therefore, the book which makes them central to science is also concerned to deny, at least by strong implication, that art can readily be distinguished from science by application of the classic dichotomies between, for example, the world of value and the world of fact, the subjective and the objective, or the intuitive and the inductive. Gombrich's work, which tends in many of the same directions, has been a source of great encouragement to me, and so is Hafner's essay. Under these circumstances, I must concur in its major conclusion: ‘The more carefully we try to distinguish artist from scientist, the more difficult our task becomes.’ Certainly that statement describes my own experience.