Bakr b. al-Qāsim b. Abī Thawr al-Mawṣilī , a philosopher of the early fourth/tenth century, has left us a single short treatise, Fī l-nafs ("On the soul"), preserved uniquely in MS London, British Library Add. 7473, fols. 6r-12r. This tract takes the form of a letter to Bakr's former teacher, Abū ʿUthmān Sāʿīd b. Yaʿqūb al-Dimashqī (d. after 302/914). Bakr's relationship with him provides the only clue to Bakr's floruit, which must have been around the turn of the fourth/tenth