This article highlights the theoretical importance of the intersection between philosophy and medicine in medieval Islamic times by bringing to light a yet unedited collection of treatises by Yaqūb b. Isāq al-Isrāīlī al-Maallī, a medieval physician who lived and practiced in Cairo and Damascus at the turn of the 13th century. It focuses first on one specific issue raised by Yaqūb in several treatises of this collection, namely the qualification of water by coldness rather than moisture, as stated by Aristotle in his treatise On Generation and Corruption II 3, and tries to uncover the reasons why Yaqūb relentlessly addressed this issue throughout 8 of the 9 treatises that were all devoted to the theory of the elements. We will see that behind it lied a very powerful answer to the Avicennian classification of medicine as a derivative science. What was at stake then was nothing less than the status of Islamic medicine and the question of its capacity to develop into an applied science, as advocated for instance by Yaqūb b. Isāq, despite the place which had been assigned to it by Avicenna, in the first book of the Canon, as a practical science, drawing its principles from the theoretical science of Physics but unable to reflect upon them. The article will conclude by confronting the social context of this collection of texts, by interrogating its relevance to the medical and philosophical circles of 13th century Cairo and Damascus, and by pushing the boundaries of that context into the wider and as of yet untapped literature which grew around Avicenna’s Canon in the 13th century.