Two sources of Michael Polanyi's prototypal notion of incommensurability: Evans-Pritchard on Azande witchcraft and St Augustine on conversion

Michael Polanyi argues in Personal Knowledge (1958) that conceptual frameworks involved in major scientific controversies are separated by a 'logical gap'. Such frameworks, according to Polanyi (1958: 151), are logically disconnected: their protagonists think differently, use different languages and occupy different worlds. Relinquishing one framework and adopting another, Polanyi's scientist undergoes a 'conversion' to a new 'faith'. Polanyi, in other words, presaged Kuhn and Feyerabend's concept of incommensurability. To what influences was Polanyi subject as he developed his concept of the logical gap? The. answer, as unfolded in this article, is twofold: Evans-Pritchard's Witchcraft, Oracles and Magic among the Azande and the Confessions of St Augustine.