Abstract
In this study, ʿAlī al-Qūshjī ‘s ‘definition of number’ will be analyzed in terms of unity, plurality, one, many, quantity, sum, counting, and related concepts. First, to emphasize the importance of the subject, the discussions of the ‘definition of number’ in contemporary philosophy of mathematics will be briefly reviewed. Then, ʿAlī alQūshjī’s approach to the subject will be examined through his works al-Muḥammadiyya fī al-ḥisāb and Sharh alTajrīd, and his thoughts will be analyzed. In addition, for a comparison with ʿAlī al-Qūshjī’s approach, Shams alDīn Iṣfahānī’s commentary Tasdīd al-Qawāʾid fī sharḥ Tajrīd al-ʿaqāʾid and Sayyid Sharīf’s Ḥāshiya will be briefly discussed. The background of the attitude ʿAli al-Qūshjī represented will be built on works by members of the Tabriz school of mathematics-astronomy, especially Niẓām al-Dīn al-Nīsābūrī, Ibn Hawwām, Kamāl al-Dīn al-Fārisī, and Jamāl al-Dīn al-Turkistānī, as well as Abū al-Ḥasan al-Bahmanī and ʿAlī b. al-Gharbī. Additionally, the book Miftāḥ al-ḥussāb by Jamshīd al-Kāshī of the Samarkand school of mathematics-astronomy, of which ʿAlī al-Qūshjī was a member, will be addressed. Then, the debate triggered by ʿAlī al-Qūshjī in Istanbul will be traced, focusing on mathematicians such as Fanārīzāde ʿAlī Chalabī and the accounting mathematician Kātib ʿAlāʾ al-Dīn Yūsuf. A brief evaluation will be made of the projections of all these discussions in the work of Taqī al-Dīn Rāṣid.