Tusi, Nasir Al-Din Al

(full name, Abu Jafar Muhammad ibn Muhammad ibn Hasan Abu Bakr Nasir al-Din al-Tusi). Born Feb. 18, 1201, in Tus; died June 25, 1274, in Baghdad. Scholar, encyclopedist, and statesman.

Nasir al-Din al-Tusi first served with the Ismailians of Alamut. In 1256 he joined the Mongol Il-khan Hulagu (Hülegü), later becoming his personal counsellor and secretary. He supervised the construction of the Maragheh Observatory. His treatise on state finances contains detailed information about the tax system of the Hulaguid state. Al-Tusi also wrote a chapter about the taking of Baghdad by the Mongols in a work of the Persian historian Joveyni. He was the author of The Ethics of Nasir, a work widely known in the East.

Al-Tusi’s philosophical views were influenced by the Azerbaijani philosopher Bakhmaniar. Al-Tusi’s Commentaries on the Philosophy and Logic of Ibn Sina (Avicenna), in which he refutes the views of Ibn Sina’s ideological opponents, is of great value. The tenth chapter of his book on logic Asas al-iqtibas (The Foundations of Borrowing) and his work Meyar al-ashar (The Criterion for Poetry) are concerned with the theory of poetry. An astronomical catalog, the Zij al-Il-Khani, was compiled under al-Tusi’s supervision.

Al-Tusi also wrote works on mathematics, including A Treatise to Cure Doubts Regarding Parallel Lines and Exposition of Euclid, in which the postulate of parallel lines is discussed in connection with the sum of the angles of a triangle, and a Treatise on the Complete Quadrilateral, in which plane and spherical trigonometry are expounded as an independent discipline.