This dissertation offers a systematic study of al-Rāzī’s philosophy of mind, exploring his position on the nature of the soul as it developed throughout his intellectual life, with a special focus on al-Maṭālib. In treating the subject matter of the soul, al-Rāzī employs a dialectical methodology (thesis, antithesis and synthesis) in which he adopts a critical stance against both the theologians’ materialism and the philosophers’ (namely Avicenna’s) immaterialism, before constructing his own dualistic theory. The dissertation is therefore set out according to al-Rāzī’s own dialectical schema, whereby I first investigate al-Rāzī’s analysis and critique of the theologians’ materialism, then explore his refutation of Avicenna’s immaterialist doctrine, namely the latter’s indivisibility argument, before looking in detail at al-Rāzī’s own eclectic dualistic theory. I divide my dissertation into five chapters: the first offers a philological study of al-Rāzī’s al-Maṭālib, presenting various observations on a potential relationship between al-Maṭālib and al-Rāzī’s book published under the title Kitāb al-Nafs. The second provides a chronological exploration of al-Rāzī’s positions on the nature of the soul throughout his works; the third deals with his discussion and critique of the theologians’ materialism; the fourth discusses his critique of Avicenna’s indivisibility argument; and finally Chapter 5 dwells on al-Rāzī’s own theory of the soul (his substance dualism).