The famous philosopher and scientist Abū ʿAlī b. Sīnā (d. 428/1037) had an exceptional command of all the subjects on which he wrote. He is especially known for his many writings in logic, philosophy, and medicine. His influence was such that even in Europe, his works on physics, metaphysics and medicine in particular, were widely studied until the beginning of modern times. A keen mind, he had a full understanding of the inner structure of the Islamo-Hellenistic tradition that he perpetuated and in places helped to develop and reshape. This is not only borne out by his many writings, but in some instances also by his explicit accounts of the sciences and their divisions. This article contains an edition of one such account, of which only two copies have been identified so far. It will be argued (against Biesterfeldt) that the text in question is likely to have been written in Bukhārā when Avicenna was still in his early twenties. Moreover, it will be shown that it could very well be that the text was actually copied from his famous Al-ḥāṣil wal-maḥṣūl (Harvest reapings), a philosophical encyclopaedia in twenty volumes long since lost. The absence of algebra and a philosophical rather than a religious foundation of the sciences finally, are important clues to Avicenna's perspective on the rational sciences early in his career.