We have considered Galen’s views on the establishment of secure theoretical knowledge about the natural world. We turn to his views on scientific method in the more specifically medical context. Galen names three medical “sects”, in relation to which he positions his own methodology: the Dogmatists or Rationalists (dogmatikoi, logikoi), the Empiricists (empeirikoi) and the Methodists (methodikoi); and he explores the differences between them especially in SI. In fact, only the latter two names correspond to self-styled groupings with explicit school doctrines; the term Rationalist or Dogmatist, meanwhile, is a catch-all referring to any doctor who functions with a (non-Methodist) theory regarding the internal workings of the body. (See Walzer and Frede 1985, introduction; Hankinson 1991a, 2008a.) The Methodists are a theoretically minimalist sect, who conceptualize the pathology of the body in terms of two basic “commonalities” (koinotētes), consisting in increased fluidity or increased restriction through the pathways (poroi) of the body; the Empiricists avoid any statement about physiology, their treatments being based on an inductive procedure from similarity with past cases, the “transition from the similar” (metabasis tou homoiou), with no commitment to any physiological theory; a Dogmatist may be any (non-Methodist) physician with a theory about the internal workings of the body and about disease aetiology.