This article presents an edition and translation of the Treatise on the Immortality of the Rational Soul of Man According to Aristotle’s Opinion (M. fī baqāʾ al-nafs al-nāṭiqa min al-insān ʿalā raʾy Arisṭūṭālis) by the Christian philosopher and physician Abū al-Ḫayr al-Ḥasan ibn Suwār (942-post 1017). Its importance lies in the fact that: (i.) it provides the sole testimony concerning the doctrine of the immortality of the soul developed by a philosopher who was a significant representative of the intellectual and exegetical life of his day; (ii.) it constitutes concrete evidence of the fact that the philosophical activity of the Baghdad Aristotelians did not concern only Aristotle’s logic, physics, and metaphysics, but also psychology and ...