Abstract
The Hungarian-born intellectual Arthur Koestler produced a wide-ranging corpus of written work throughout the mid twentieth century. Despite being the subject of two huge biographies in recent years, his long-standing engagement with numerous scientific disciplines remains unexplored. This paper situates Koestler's scientific philosophy within the context of mid-twentieth-century science and explores his relationship with key figures, including Dennis Gábor, C. H. Waddington, Ludwig von Bertalanffy and J. R. Smythies. The argument presented is threefold. First, surprisingly, serious scientists, particularly in the biological sciences, took Koestler's scientific work seriously; second, despite Koestler's best efforts, his allies could not agree on a single articulation of anti-reductionism; and third, the reductionist/anti-reductionist debates of the mid twentieth century constituted a battle for the authority to speak on behalf of 'science' that led Koestler into direct conflict with figures including Peter Medawar. By exploring the community associated with Koestler, the paper sheds new light on the status of scientific authority and the relationship between scientists' metaphysical beliefs and their practices.