In the post-classical period of Arabic philosophy and medicine, Aristotle's and Galen's views on pain, and its relation to the body and soul were mediated in large part by Avicenna's Canon of Medicine and Avicenna's On Soul. By the beginning of the thirteenth-century, the Canon, especially Canon 1 (Generalities, K. al-Kullīyāt) had begun to exert considerable influence on Arabic philosophy and medicine, inaugurated primarily by Fakhr al-Dīn al-Rāzī's critical (or "verifying") commentary on Canon 1. In his commentary on Canon 1.3, Rāzī criticises how Avicenna and Galen understood the nature of pain and its relation to the body and soul. Rāzī's commentary on Canon 1 gained wide notoriety. His comments on pain in particular appear to have provoked ire of the erudite Melkite Christian physician Abū al-Faraj Ibn al-Quff. In his commentary on the Hippocratic Aphorisms, Ibn al-Quff's commentary carries out an extended and extraordinarily detailed rebuttal of Rāzī's doctrine of pain and pleasure. This rebuttal takes Ibn al-Quff far from Galen's commentary on the Aphorisms. This exchange between these two great thirteenth-century thinkers illustrates how Avicenna's Canon as well as his philosophical works influenced the development of post-classical Arabic medicine. It also illustrates, however, how by the end of the thirteenth-century Fakhr al-Dīn's influence had spread beyond Transoxiana and Iran, and beyond philosophical, theological and legal scholarly circles, and had come to influence Arabic scholastic medicine in Transjordan and the Levant.