The psychoanalytical case history was in many ways the pivot point of John Forrester’s reflections on case-based reasoning. Yet the Freudian case is not without its own textual forebears. This article closely analyses texts from two earlier case-writing traditions in order to elucidate some of the negotiations by which the case history as a textual form came to articulate the mode of reasoning that we now call ‘thinking in cases’. It reads Eugène Azam’s 1876 observation of Félida X and her (...) ‘double personality’—the case that brought both Azam and Félida to prominence in late 19th-century French science—against a medico-surgical case penned by the Bordeaux physician in the same decade. While the stylistics of Azam’s medical case mirror its epistemic underpinnings in the ‘vertical’ logics of positivist science, the multiple narratives interwoven in Félida’s case grant both Azam and his patient the role of knowledge-making actors in the text. This narrative transformation chimes with the way Azam reasons ‘horizontally’ from particulars to Félida’s singular condition, but sits in tension with his choice to structure the observation along a ‘vertical’ axis. Between the two, we glimpse the emergence of the psychological observation as a mode of writing and thus of thinking in cases. (shrink)