This paper demonstrates the evolving conceptualizations of the medical discipline in the classical Islamic world. It in addition draws attention to the implications of these conceptualizations for medical knowledge production. By comparing Ibn Rushd’s view of medicine promulgated in his Principles of Medicine (Kulliyat fi l-Tibb) to that of Ibn Sina as proposed in his Canon, the paper shows the extent to which the disciplinary boundaries of the medical field were considered negotiable during the classical Islamic period. The paper demonstrates that Ibn Rushd (1126-1198 AD) rejected the widely accepted view of Ibn Sina (980-1037 AD) which held that medicine was an art with both a practical and theoretical division. Rather, in the Kulliyat, Ibn Rushd advocated for the medical art to be solely practical. To practice his art, Ibn Rushd argues that a physician (tabib) must draw from three ancillary arts; that of dissection (tashrih), experimental medicine (al-tibb al-tajribi), and natural science (ilm al-tabi’i). The physician must emphatically not take part in theorising himself but leave medical thinking to natural scientists. Ibn Rushd arguably arrived at this view a posteriori having compared Galen, the physician, to Aristotle, the natural scientist. As a staunch Aristotelian, Ibn Rushd despises the theoretical work of Galen and where evidence compels him to accept Galenic theory over Aristotle, he does so while refusing to reject the broader Aristotelian physiological framework. He claims that Galen, as a physician, should not have engaged in theory, but have focused on treating patients. In his refusal to accept the theoretical contributions of medical thinkers, Ibn Rushd is unwilling to see beyond the Aristotelian paradigm even when contradictory evidence requires him to do so. Moreover, his selective preference for natural scientists could have limited the participation in theoretical knowledge production by physicians. However, physicians continued to engage in theoretical medical thinking throughout the Islamic world clearly undisturbed by Ibn Rushd’s attempt to narrow the field. Nevertheless both his endeavour and the more successful approach of his predecessor Ibn Sina shed crucial light on the varied disciplinary reflections that circulated in the medieval Islamic world.