Mohammad Ibn Mohammad Ibn Al Hassan Al Tusi, or Nasir Al Deen Al Tusi, stood out among Persian scholars. While true philosophical activities almost ceased after Ibn Rushd, at the end of the 12th century, a renewal occurred in Persia through the intellectual efforts and political involvement of Al Tusi (known throughout the Muslim world as Khawajah Nasir), a polymath who became the father of trigonometry and who defended such scholars as Ibn Sina and Al Farabi even as they were scorned by misguided theologians.
He added value to our understanding of metaphysical argumentation and terminology in Twelver Shiite theology and left a lasting impact on the study of sciences through both his original contributions to mathematics and at the observatory in Maragheh, which the Mongol Hulagu Khan established especially for him.
Life and times
Al Tusi was born in Tus, close to the city of Mashhad in northeastern Iran, on 18 February 1201. The 13th century witnessed various conquests that saw Islam stretch from Europe to China, a time when Mongols expanded their territories, often running into Muslim dynasties and resulting in atrocities. The bloodiest century until the 20th severely limited what scholars accomplished. In 1214, when the Muslim world fell to the great Mongol leader Genghis Khan, a 13-year-old Al Tusi found refuge in nearby Nishapur.
Al Tusi became a serious student, exploring religious texts and Twelver Shiite jurisprudence, perhaps to follow in his father’s footsteps, a well-known jurist. He then turned to Ismaili teachings, which were influenced by the Neoplatonic speculations of thinkers in the 9th and 10th centuries and whose doctrine embraced the concept of an infallible Imam. Al Tusi came to doubt that without the guidance of an infallible Imam, the intellect could reach the truth, and while he was steeped in theological courses, he was fortunate to receive private tutoring from his uncle in several science courses. This changed his life. He was introduced to logic, philosophy, mathematics, medicine, physics and astronomy, transforming him into a polymath. In Nishapur, then a centre of learning founded by the Sasanian king, Shapur, the precocious boy studied philosophy under Fareed Al Deen Damad. It was in the famed city that Al Tusi discovered mathematics with the help of two renowned theoreticians, Mohammad Hasib and Kamal Al Deen Ibn Yunus, who taught him algebra and geometry.
The Ismaili ruler Nasir Al Deen Abdul Rahman welcomed him among the Hashashin (Assassins) Order, which saw the young man serving at the court. Inspired by the Ismailis, Al Tusi wrote some of his best work on logic, philosophy, mathematics and astronomy, including the “Akhlaq-i-Nasiri” in 1232, a treatise on ethics dedicated to Nasir Al Deen Abdul Rahman. When the Mongol invasion of Iran in the mid-13th century resulted in a near-total destruction of Ismaili strongholds, Al Tusi negotiated the surrender of the grand Ismaili master to the Mongol conqueror Hulagu— a grandson of Genghis Khan — who was impressed enough by Al Tusi’s skills to treat him with great respect.
Maragheh observatory
After Baghdad was conquered in 1258, Al Tusi received a new writ, that of the head of religious endowments. Hulagu also authorised the building of an observatory and library at Maragheh, where the scholar led a team of scientists and mathematicians from as far away as China.
Maragheh, in the Azerbaijan region of northwestern Iran, thus became the Muslim world’s premier learning centre after 1262 and included a 4-metre-wall quadrant made from copper as well as Al Tusi’s invention, an azimuth quadrant that provided an angular measurement in a sphere. Remarkably, the work of the observatory stood out as the most accurate tables of planetary movements until that time. In fact, the “Zij-i-Ilkhani” (the Ilkhanic Tables), first written in Farsi and later translated into Arabic, contained tables for computing the positions of the planets. It took 12 years to compose, and provided the scientific community with a catalogue of known stars. It may be accurate to state that between Ptolemy’s unique model of the planetary system and the heliocentric Copernicus discoveries, there were no significant astronomical findings other than Al Tusi’s.
In his major astronomical treatise, “Al Tadhkirah Fi ‘ilm Al Hay’ah” (Memoir on astronomy), Al Tusi explained how he created a model of lunar motion that was different from Ptolemy’s, based on the principle of eight uniformly rotating spheres. This explained the irregularities of lunar motion, and his assertion that the maximum difference in longitude between the two theories amounts to ten proved accurate.
Al Tusi thus relied on a theorem, which Copernicus re-devised nearly 250 years later, and became known as the “Tusi-couple”. The theorem addressed the dilemma of linear motion, as it aimed to correct Ptolemy’s ideas, which did not factor in the principle of uniform circular motion.
Al Tusi invented a mathematical device in which a small circle rotated inside a larger circle twice its diameter. As the rotations of the circles caused a point on the circumference of the smaller circle to move back and forth in linear motion along the diameter of the larger circle, Al Tusi found a solution for the latitudinal motion of the inferior planets. Whether Copernicus discovered it in Al Tusi’s work or he took it from the commentary on the first book of Euclid by Proclus is not known. Suffice it to say that Al Tusi was as skilled an astronomer as any. His astrolabes were so sophisticated that all previous instruments simply became museum pieces.
Among his many contributions were the Al Tusi “if-then” and “either-or” propositions, which clarified disjunction problems and conditional intentions. His commentaries on Greek texts, including revised Arabic versions of works by Euclid, Archimedes and Ptolemy, among others, served generations of Arab scholars. In all of his work, Al Tusi discussed objections of earlier mathematicians, arguing that comparisons were legitimate ways of advancing knowledge. Perhaps his most important commentary was on Ptolemy’s “Almagest”, which he published in 1247 under the title, “Tahrir Al Majisti” (Commentary on the Almagest); he introduced various trigonometrical techniques to calculate tables of sines. Indeed, Al Tusi’s mathematical contribution established trigonometry as a discipline in its own right, rather than as just a tool for astronomical applications. In his “Treatise on the Quadrilateral”, for example, he gave the first exposition of the whole system of plane and spherical trigonometry — which build on his famous sine formula for plane triangles, a/sin A = b/sin B = c/sin C — that led to the discovery of the law of tangents for spherical triangles, changing mathematics for good.
Philosophical Ideas
The end of Al Tusi Ismaili period also marked his return to Twelver Shiism, as he reformulated Imami theology in philosophical terms. Few scholars have been as influential in Shiite realms — the only fair comparison is the kind of impact that Fakhr Al Deen Al Razi (1149-1209) has had among the Sunnis. When Al Tusi died in Baghdad in 1274, he was buried, according to his last wishes, beside the shrine of the seventh Twelver Imam, Musa Ibn Ja‘far.
A courageous intellectual, he believed in the need for reason to be sustained by a non-rational (or supra-rational) guarantor, which was incredible to say the least. Indeed, one of the reasons why he moved to Twelver Shiism — with its doctrine of the hidden, inaccessible Imam — was that he was persuaded of the intrinsic ability of the intellect. This was a sectarian shift par excellence, which raised many questions about his doctrinal loyalties. Be that as it may, Al Tusi was convinced that preconceived ideas did not advance the cause of truth as he defended Ibn Sina’s theory of identity of form between the knower and known. This question concerned the nature of God’s knowledge, which he also accepted, positing that the knowledge of the First Intellect, and consequently of the entire universe, was identical to God’s existence. Human beings derived knowledge through forms and representations as well as through presence, which was as clear as Al Tusi could be, providing clear explanations in sharp contrast to Ibn Sina’s dense prose that confused many.
Focus on ethics
There are two works of Al Tusi on ethics worthy of attention, the “Akhlaq-i-Muhtashami” (Muhtashamean Ethics) and the “Akhlaq-i-Nasiri” (The Nasirian Ethics), both written in Farsi and translated into several languages. The first, written for Nasir Al Deen Abdul Rahman, was commissioned to help with the ruler’s own political duties, the reason it reads like a straightforward list of recommendations. The second, although dedicated to the same leader, was more of a philosophical discourse that examined ethics (akhlaq), domestic economics (tadbir-e-manzil) and politics (siyasat-e-mudun). It offered specific practical features.
The akhlaq delves into psychology, along with what character means and what virtues stand for. The section on tadbir-e-manzil, which worked around Bryson’s epochal “Management of the Estate” (Oikonomikos Logos) study, offered advice on the key private concerns of the Roman elite: how to get rich, how to manage slaves, love and marriage, and how to bring up children. The section on siyasat-e-mudun relied on Al Farabi’s “Kitab Al Siyasah Al Madaniyyah” (The Political Regime), which tackled the virtue of love (mahabbah) as the cement of societies. Reading such contents reminded one that most orientalist writers seldom accepted the notion of Muslims strongly believing in love. Nevertheless, it took “Lawrence of Arabia” to broach the subject, when a bedouin once told Lawrence: “Love is from God; and of God; and towards God.” Of course, this shocked Lawrence, though few made the connection with ethics.
Like the Arab bedouin, Al Tusi maintained that his work transcended sectarian differences, and that the love of ethics was a universal quest. Naturally, he affirmed the intellect’s capacity to view normative values without referring to complex religious norms, even if his search for justice also satisfied Shiite theology. It was a long-lasting mission, one that encouraged the pursuit of knowledge according to clear ethical norms, and that was gradually absorbed by scientists as well as clerics.
Legacy to Arabs and Muslims
Beyond the Muslim World, scientists recognised Al Tusi’s contributions by naming after him a 60-kilometre-diameter lunar crater located in the southern hemisphere of the moon. It was known as the Nasridin. In 1979, the Soviet astronomer Nikolai Stepanovish Chernykh named planet 10269 as the Tusi, while one of Iran’s public universities in Tehran was named after the scholar (Khajeh Nasir Toosi University of Technology).
Perhaps the ultimate accolade came from the sociologist Ibn Khaldun (1332–1406), who considered Al Tusi to be the greatest Persian scholar ever, someone who truly added value to mankind. Al Tusi’s influence was immense as he single-handedly revived the study of science after a period of abeyance. By assembling competent scholars and scientists at Maragheh, Al Tusi made significant contributions to mathematics and astronomy, both of which opened new avenues to rekindle interest in Islamic philosophy and even theology.
This article is the Sixth of a series on Muslim thinkers who greatly influenced Arab societies across the centuries.
Dr Joseph A. Kéchichian is the author of the forthcoming Legal and Political Reforms in Saudi Arabia (Routledge, 2012).
Selected readings
“Nasir al-Din al-Tusi, Akhlaq-i-Nasiri” (The Nasirian Ethics), translated by G. M. Wickens, London: Routledge, 2011.
“Nasir al-Din al-Tusi, Asas al-Iqtibas” (The Ground for the Acquisition of Knowledge), edited by Mudarris Radawi, Tehran: Tehran University Press, 1947 (Al Tusi’s major logical text, in Farsi)
“Nasir al-Din al-Tusi, Sayr wa Suluk” (Contemplation and Action), edited and translated by Seyyed Jalal Hosseini Badakhchani, London: Institute for Ismaili Studies, 1997.
“Nasir al-Din al-Tusi, Sharh al-Isharat” (Commentary on the Isharat), in Sulyman Dunya, ed., “Ibn Sina: al-Isharat wal-Tanbihat”, Cairo: Dar al-Ma‘arif, 1957-60.
Hamid Dabashi, “Khawajah Nasir al-Din al-Tusi: The Philosopher/Vizier and the Intellectual Climate of His Times”, in Seyyid Hossein Nasr and Oliver Leaman, eds., “History of Islamic Philosophy”, London: Routledge, 1995, pp. 527-584.
Wilferd Madelung, “Nasir al-Din Tusi’s Ethics Between Philosophy, Sh‘ism, and Sufism”, in Richard G. Hovannisian, ed., “Ethics in Islam”, Malibu, CA: Undena, 1985, pp. 85-101.
Parviz Morewedge, “The Analysis of ‘Substance’ in Tusi’s Logic and in the Ibn Sinian tradition”, in George F. Hourani, ed., “Essays on Islamic Philosophy and Science”, Albany, NY: State University of New York Press, 1975.
