Evidence-based medicine emerged in connection with struggles for clinical authority in the second half of the twentieth century, as patient-centred medicine and community-oriented medicine presented challenges to laboratory-oriented medicine. The renowned medical researchers Alvan Feinstein and Archie Cochrane helped to develop the new models of patient-centred and community-oriented medicine respectively. They made important contributions to methodological reflections in medicine, and also contributed to social theories about clinical medicine and health care, challenging and criticizing in different ways dominant ontological medical understandings (such as essentialist conceptions of disease and illness). The medical ontologies of patient-centred and community-oriented medicine comprise different (partly incompatible) perspectives on what constitutes standards of evidence, something reflected, for example, in Feinstein and Cochrane’s contrary views on the importance of controlled trials. The analysis of their work in this article illuminates the connection between medical ontologies, standards of evidence and the political in general, reminding us of the need to explore the role of politics in discussions of evidence-based medicine.