The introduction asserts that the different causal, spatial, and comparative relations in Plato's Timaeus generated a model of knowledge that denies a strict separation between the disciplines. I contrast the dialogue's epistemic vision with the prevailing hierarchies of knowledge developed by ancient thinkers, including Plato himself, which ranks medicine below philosophy because it is a technē ('art'), deals with the body, and its practitioners were often enslaved or freedpersons. I argue that Galen's expansive refiguring of medicine's boundaries -- his 'boundary work' -- is part of a tactic to improve his profession's credibility and his own authority. After outlining my approach to science as a discursive practice, I consider how Galen's philosophical training enabled him to exploit the epistemic possibilities of the Timaeus, which seems to recognize that knowledge can be divided and bounded differently by each knower. I conclude by proposing that Galen’s own role in interfacing Arabic readers with the dialogue called for Arabic doctors and philosophers to reevaluate their own categories and taxonomies of knowledge, which had been shaped by late-antique epistemologies.