Naṣīr al-Dīn al-Ṭūsī (1201–1274)

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Naīr al-Dīn al-ūsī (12011274) is a Shiʿa Iranian author of some two hundred treatises in a number of disciplines, including philosophy, mathematics, astronomy, mysticism, and theology.

Life and Times

Naīr al-Dīn was born in the city of Tus in the province of Khurasan in northwestern Iran, the first area to be devastated by the Mongolian invasion of the Middle East by Helagu Khan (12171265), grandson of Genghis Khan (1167?1227). After completing his formal studies, al-ūsī carried out research and publications under the patronage of various Ismaili rulers from 1227 until 1256, when he assisted the Ismaili ruler to surrender to Helegu Khan, who employed al-ūsī as his adviser until Helagu's death and then joined Abaq (12651282) until his own death. Al-ūsī accompanied Helagu Khan in the Monogol attack on the last Sunni caliph in Baghdad, after which he built an observatory at Maragha in Azarbayijan in northwest Iran. There he spent the rest of his life in supervising innovations in astronomy and mathematics; in addition, he attracted the patronage of the Mongol ruler toward scientists, Shiʿa theologians, and writers on mysticism.

Cosmogony and Its Ethics

In formulating his views on the existence of God, al-ūsī appeals to the Avicennan doctrine that God has no (external) cause; because entities are known by their causes, there cannot be any affirmative scientific type of knowledge (ʿilm ) of God. In this light, one needs to note the Qurʾanic indication that the divine expresses creation in the language of command (amr ) and in the logos of be/make (kun ), which express the good intention of the creator as the paradigm of action. Here al-ūsī proffers an Ismaʿili doctrine that the Imam is a physical incarnation, or an earthly instantiation of the divine goodwill. As a self-caused entity God must be a unity; and as a unity he can only create one entity, namely the Necessary Existent (al-wajib al-wujud ), which has been equated with the First Intelligence (nous ), from which the rest of the universe emanates in a series that has been represented by Neoplatonists as follows: After the Universal Soul emanates, the Individual Souls come forth and finally matter. Whereas Ibn Sīnā does not equate his Necessary Existent with the God of Islam, the major Ismaʿili theologian prior to al-ūsī, Nāir Khosrow, explicitly states that God creates the Necessary Existent, from whom the rest of the universe then emanates. A Zoroastrian and a Nietzschian type of ethics is implied in al-ūsī's cosmogony, where the good is associated with the good intention of the agent in the context of imitating the Imam.

The Theodicy of Soft Determinism

Al-ūsī held that free will, determinism, and indeterminism are metalinguistic terms for explaining actions. A system is determined if the future can be predicted from a knowledge of all events and laws. When people are unaware of causes of behavior, free will is attributed to an agent, whose will corresponds with necessityfor example, a pregnant mother who wills the birth of her child. Having free will does not imply that the will is free and indeterminism is true. Total freedom is an intentional state of an agent that is achieved through knowledge of causes of events and one's "love"-receptivity to accept one's fate-role in the best of all possible worlds, as is exemplified by parents who graciously accept the facts of aging and welcome their children's well-deserved authority. In this tenor, al-ūsī's system resembles Gottfried Leibniz's view of the best of all possible worlds. H. A. Wolfson notes that such a resemblance is due to Leibniz's copying Spinoza's theodicy, which in turn can be traced to the influence of Avicennan thought on Maimonides. Following Tolstoy's view that "free will is the essence of life, but it is an illusion," al-ūsī holds that free will is an intentional concept. "Will per se," he states, "cannot be cause of any action in a mind-independent world" (pm: see Metaphysics of Tusi, p. 3940). Al-ūsī holds that to God, who is a unity, neither free will nor determinism applies, because an agent is free, if his or her will agrees with necessity (which implies a duality in the agent).

Refutation of Matter

Through a number of proofs al-ūsī points out the incompatibility of the notion of the ultimate indivisible material substance of early Sunni theologians. Consider, for example, the following 4 by 4 arrangement of material substances:
A 0 0 0 0 B
0 0 0 0
0 0 0 0
C 0 0 0 0 D
Imagine a triangle, where hypotenuse is BC, the base is CD, and a side is BD. According to the atomic theory of homogeneous indivisible matters with no space between them, the base CD would equal the hypotenuse, which is BC. But this conclusion contradicts the Euclidean rule that a hypotenuse (BC) is longer then the base CD. Upholding the absoluteness of the Euclidean geometry, al-ūsī uses this and seven other proofs to refute the material theory of substance.

The Application of Philosophical Analysis to Different Senses of Infinity

Al-ūsī faces the following dilemma: As a philosopher he has to agree with Aristotle and Ibn Sīnā in holding that the "actual infinite" is not a legitimate notion, yet as a mathematician he needs to employ "infinity" in the theory of numbers. Moreover, as a phenomenologist he had to use a continuum to explain perception and a continuum is often expressed by real numbers. In a clever manner that resembles R. Carnap's celebrated method of reconstructionalism and fits into the tradition of philosophical analysis, al-ūsī proffers the following solution. He begins by distinguishing different senses of infinity in their application to various domains such as the "syntactical" realm, the actual world, the phenomenology of experiences such as perception, and the like.

Intentional Mystical Virtues

Al-ūsī wrote several texts on intentional analyses of the moral psychology of mystical experience. A number of investigators, such as Wilfred Madelung, hold that al-ūsī's main purpose was to propose a practical experiential praxis of mysticism of the Shiʿa kind that was an alternative to the Sunni school of Ibn ʿArabi that had been advocated by Al-Qunawi.

See also Aristotle; Avicenna; Carnap, Rudolf; Determinism and Freedom; Ibn al-ʿArabī; Islamic Philosophy; Leibniz, Gottfried Wilhelm; Logos; Maimonides; Neoplatonism; Spinoza, Benedict (Baruch) de; Tolstoy, Lev (Leo) Nikolaevich.


Dabashi, H. "Khwajah Nasir al-Din al-Tusi: The Philosopher/Vizier and the Intellectual Climate of His Times." In History of Islamic Philosophy, edited by Sayyed H. Nasr and Oliver Leaman, 527584. London: Routledge, 1998.

Metaphysics of Tusi. Translated by Parviz Morewedge. New York: Institute of Global Cultural Studies, 1992.

Morewedge, P. "The Analysis of 'Substance' in Tusi's Logic and in the Ibn Sinian Tradition." In Essays on Islamic Philosophy and Science, edited by G. Hourani. Albany, NY: Suny Press, 1975.

Naīr al-Dīn al-ūsī. Contemplation and Action: The Spiritual Autobiography of a Muslim Scholar, edited and translated by S. J. Badakhsahni. London: I. B. Tauris, 1998.

The Nasirean Ethics by Nasir al-Din Tusi. Translated by G. M. Wickens. London: George, Allen and Unwin, 1964.

Parviz Morewedge (2005)