ALī AL-QūSHJī (ABū AL-QāSIM ALā AL-DīN ALī IBN MUHAMMAD QUSHJī-ZāDE)

(b. probably Samarqand, early fifteenth century; d. Istanbul, Turkey, 1474)

astronomy, natural philosophy.

Ali al-Qushji was a philosopher-theologian, mathematician, astronomer, and linguist who produced original studies in both observational and theoretical astronomy within fifteenth-century Islamic and Ottoman astronomy. He contributed to the preparation of Ulugh Beg’s Zij at the Samarqand Observatory, insisted on the possibility of the Earth’s motion, and asserted the need for the purification of all the scientific disciplines from the principles of Aristotelian physics and metaphysics.

Life. Qushji was the son of Ulugh Beg’s falconer, whence his Turkish name Qushci-zade. He took courses in the linguistic sciences, mathematics, and astronomy as well as other sciences taught by scholars in the circle of Ulugh Beg. These included Jamshid al-Kashi, Qadizade al-Rumi, and Ulugh Beg himself.

In 1420 Qushji secretly moved to Kirman, where he studied astronomy (c. 1423–1427) with Molla Jami the mathematical sciences. Upon his return to Samarqand around 1428, Qushji presented Ulugh Beg with a monograph (Hall ishkal al-qamar) in which he solved a variety of problems; Ulugh Beg was reported to have been quite pleased. Sources say that Ulugh Beg referred to Qushji as “my virtuous son” (“ferzend-i ercümend,” Nuruosmaniye MS 2932, f. 2b). Indeed, after the death of Qadizade, it was Qushji whom Ulugh Beg commissioned to administer the observational work at the Samarqand Observatory that was required for his Zij (astronomical handbook). Qushji, often referred to as “Sahib-i rasad” (head of observation), contributed to the preparation and correction of the Zij, but it is unclear to what extent and at what stage. This question becomes especially problematic in view of Qushji’s criticisms of it and his pointing out of mistakes, in his Sharh-i Zij Ulugh Beg(Commentary on Ulugh Beg’s Zij).

Upon Ulugh Beg’s death in 1449, Qushji, together with his family and students, spent a considerable time in Herat, where he wrote his theological work Sharh alTajrid, a commentary to Nasir al-Din al-Tusi’s (d. 1274) work al-Tajrid fi ilm al-kalam, which he presented to the Timurid Sultan Abu Said. After Abu Said’s defeat by Uzun Hasan in 1469, Qushji moved to Tabriz, where he was welcomed by the latter. It is said that Qushji was sent to Istanbul to settle a dispute between Uzan Hasan and Mehmed the Conqueror; after accomplishing the mission, he returned to Tabriz. However, around 1472 Qushi, together with his family and students, left permanently for Istanbul either on his own or because of an invitation from Sultan Mehmed.

When Qushji and his entourage approached Istanbul, Sultan Mehmed sent a group of scholars to welcome them. Sources say that in crossing the Bosporus to Istanbul, a discussion ensued about the causes of its ebb and flow. Upon arrival in Istanbul, Qushji presented his mathematical work al-Muhammadiyya fi al-hisab to the sultan, which was named in his honor.

Qushji spent the remaining two to three years of his life in Istanbul. He first taught in the Sahn-i Thaman Madrassa (founded by Sultan Mehmed); then he was made head of the Ayasofya Madrassa. In this brief period Qushji educated and influenced a large number of students, who, along with his writings, were to have an enormous impact on future generations. He died in 1474 and was buried in the cemetery of the Eyyub mosque.

Prolific Writer. Qushji, especially when compared with his contemporaries such as Kashi and Qadizade, was a remarkable polymath who excelled in a variety of disciplines including language and literature, philosophy, theology, mathematics, and astronomy. He wrote works in all these fields, producing books, textbooks, and short monographs dealing with specific problems. His commentaries often became more popular than the original texts and themselves became the subject of numerous commentaries. Thousands of copies of Qushji’s works are extant and many were taught in the madrassas.

Qushji’s philosophy of science, which had important repercussions for the history of astronomy, is contained in his commentary to Tusi’s Sharh al-Tajrid. Besides being one of the most important theological works in Islam, this commentary lays down the philosophical principles of Qushji’s conception of existence, existents, nature, knowledge, and language. As for the mathematical sciences, Qushji in general tried to free them from Hermetic-Pythagorean mysticism and to provide an alternative to Aristotelian physics as the basis for astronomy and optics. He sought to define body (jism) as being predominantly mathematical in character. Qushji claimed that the essence of a body is composed of discontinuous (atomic) quantity while its form consists of continuous (geometrical) quantity. When a body is a subject of the senses, it then gains its natural properties (qualifications).

One consequence of Qushji’s anti-Aristotelian views was his striking assertion that it might well be possible that the Earth is in motion. Here Qushji followed a long line of Islamic astronomers who rejected Ptolemy’s observational proofs for a stationary Earth; Qushji, though, refused to follow them in depending on Aristotle’s philosophical proofs, thus opening up the possibility for a new physics in which the Earth was in motion. Qushji’s views were debated for centuries after his death, and he exerted a profound influence on Ottoman-Turkish thought and scientific inquiry, in particular through the madrassa and its curriculum. His influence also extended to Central Asia and Iran, and it has been argued that he may well have had an influence, either directly or indirectly, upon early modern European science, to which his ideas bear a striking resemblance.

Qushji wrote five mathematics books, one in Persian and four in Arabic. His Risala dar ilm al-hisab (Persian), written during his stay in Central Asia (along with his enlarged Arabic version of this work, al-Risala al-Muhammadiyya fi al-hisab), were taught as a mid-level textbooks in Ottoman madrassas. In these works, in accordance with the principles he laid down in the Sharh al-Tajrid, he tried to free mathematics from Hermetic-Pythagorean mysticism. As a result, Ottoman mathematics took on a practical character, which hindered traditional studies such as the theory of numbers.

Astronomy. In the field of astronomy, one of Qushji’s most important contributions is in the observational program for the Zij-i Ulugh Beg and in his corrections to the work, both before and after publication. In addition, he produced nine works on astronomy, two in Persian and seven in Arabic. Some of them are original contributions while others are pedagogical. In his theoretical monograph entitled Fa ida fi ishkal utarid, Qushji criticizes and corrects opinions and ideas pertaining to Mercury’s motions mentioned in Ptolemy’s Almagest. Another work is his Risala fi asl al-khariji yumkinu fi al-sufliyayn, which deals with an eccentric model instead of epicyclical models for both inner and outer planets; it has vital importance for a sun-centered cosmology-astronomy, on the path to Copernicus through Regiomontanus.

Qushji’s Risala dar ilm al-hay a (Persian), written in Samarqand in 1458, was commonly used as a teaching text; there exist more than eighty manuscript copies of it in libraries throughout the world. It was also translated into Turkish. Two commentaries were written on it, one by Muslih al-Din al-Lari (d. 1571), the other by an anonymous author. Lari’s commentary was widely taught in Ottoman madrassas. Qushji’s Risala was also translated into Sanskrit and thus represents the transmission of Islamic astronomy to the Indian subcontinent. Qushji wrote an enlarged version of the work in Arabic under the name al-Fathiyya fi ilm al-hay a, which was presented to Sultan Mehmed in 1473. This work, taught as a middle-level textbook, was commented on by Gulam Sinan (d. 1506) and Qushji’s famous mathematician-astronomer great-grandson Miram Celebi (d. 1525). It was also translated into Persian by Muin al-Din al-Husayni and into Turkish by Seydî Ali Reîs (d. 1563). In the Risala and the Fathiyya, Qushji followed the principles he had laid down in his Sharh al-Tajrid by excluding an introductory section on Aristotelian physics, which customarily had introduced almost all previous works of this kind.

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İhsan Fazlioğlu