In the 1960s, with western narratives of technical progress at their height, Robert Matthew, then president of the Royal Institute of British Architects, and anthropologist André Leroi-Gourhan independently advocated totalising, systematic and technical models of human progress. Each model a reflection of the aims and methods of their own discipline: for the anthropologist, the evolution of Homo sapiens from Homo faber and the dissolving of human/technological boundaries; for the architect, a “collective welfare-socialism” and the systematisation of its built manifestations. Each of these models made manifest, I argue, through profoundly influential diagrams. Leroi-Gourhan’s chaîne opératoire describes the manufacture of pre-historic stone tools, whilst the RIBA’s Plan of Work describes the design and construction of buildings. Through the embodied objects and processes of these diagrams this paper sees “chaîne” and “Plan” engaging in a kind of reciprocating exchange: a diagrammed conversation revealing, for each discipline, processes occluded or overlooked in the other.