From: Thomas Hockey et al. (eds.). The Biographical Encyclopedia of Astronomers, Springer Reference. New York: Springer, 2007, pp. 564-565 Courtesy of Springer.

Miquel Forcada

Ibn Rushd: Abū al‐Walīd Muḥammad ibn Aḥmad ibn Muḥammad ibn Rushd al‐Ḥafīd

Alternate names


BornCordova (Spain), 1126

DiedMarrakech (Morocco), 10 December 1198

Ibn Rushd, one of the best‐known Islamic philosophers, challenged Ptolemy's astronomical system on philosophical grounds and made interesting theoretical contributions to the Andalusian criticisms of the Greek astronomer. Along with Ibn Bājja, IbnṬufayl, and Biṭrūjī, he wished to formulate a model for the cosmos according to Aristotelian principles – i. e., uniform and circular motions centered on the Earth – in which there was no need for eccentrics and epicycles. He was also an active and a first‐rate scholar in many other disciplines, including Islamic religion and law, medicine, and the various aspects of Hellenistic philosophy.

Ibn Rushd was born into an important family of religious scholars, but in addition to religious sciences, he also studied medicine and astronomy. We know little of his formative period; he probably studied in Cordova and Seville, learning medicine from a physician named Ibn Jurrayūl. In Seville he met Abū Jaʿfar ibn Hārūn al‐Tarjālī, a court physician who also had a profound knowledge of philosophy and mathematical sciences; Ibn Rushd became his pupil in these disciplines. In his Summary of the Almagest, Ibn Rushd himself mentions a master in astronomy named Abū Isḥāq ibn Wādiʿ, who is otherwise unknown. We know that in 1153 Ibn Rushd was in the service of the Almohads, a North African dynasty that ruled Muslim Spain (al‐Andalus) and North Africa for many years. In 1153, according to his commentaries to Aristotle's De Caelo, he observed several stars in Marrakech. In the Summary of the Almagest, Ibn Rushd goes on to say that he calculated the positions of Venus and Mercury, under the supervision of Abū Isḥāq ibn Wādiʿ, in order to check a conjunction of these planets with the Sun allegedly observed by the nephew of the Andalusian astronomer Ibn Muʿādh. These autobiographical data, together with his treatise on the Almagest, bear witness to a thorough knowledge of the fundamentals of astronomy, though he did not pursue these studies in his later years.

The personal and intellectual sides of Ibn Rushd's life are inseparable, and both were decisively determined by the fortunes of the Almohad dynasty. These rulers had attained power advocating a new interpretation of Islam that was based on the thought of Ibn Tūmārt. The new ideology had a rationalistic side applied to religion that favored the growth of rational speculation and, therefore, of philosophy and science. Furthermore, between 1163 and 1184 the dynasty was ruled by Caliph Abū Yaʿqūb Yūsuf, a man of learning interested in philosophy, medicine, and astronomy, to whom Ibn Rushd was introduced, perhaps about 1169, by the philosopher and court physician Ibn Ṭufayl. According to the chronicles, Caliph talked with the two philosophers about complex issues of faith and philosophy such as the eternity of the world. Ibn Ṭufayl later told Ibn Rushd that the caliph had complained about the obscurity of Aristotle's texts and wished to find someone able to explain them and make them more generally accessible. Whether or not this story is true, Ibn Rushd spent the rest of his life involved in this task, and became the leading commentator on Aristotle, while working for the court administration as physician, judge, and theologian. He held the posts of judge of Seville (1169) and Cordova (1171) and later became chief judge of Cordova (1182); also in 1182, he succeeded Ibn Ṭufayl as the caliph's doctor. By this time, Ibn Rushd had been promoted to the highest ranks of the Almohad hierarchy because of his intellectual activity, mainly in the fields of medicine and law. During his last years (1195–1197), he fell into disgrace and was prosecuted together with other intellectuals because Caliph al‐Manṣūr, challenged by the Christians, sought to gain the favor of a party of influential religious scholars who were hostile to the growth of philosophical speculation. He was exiled to Lucena (south of Cordova), but shortly before his death Ibn Rushd was rehabilitated and returned to the capital of the kingdom.

Ibn Rushd wrote his most important work on astronomy, the Mukhtaṣar al‐Majisṭī (Summary of the Almagest), at the beginning of his career, sometime between 1159 and 1162. Perhaps under the influence of Ibn Bājja, it was written in a period characterized by his search for those aspects of science necessary for human perfection. For this reason, his astronomical work shares many features with his medical writings, especially the Kulliyyāt fī al‐ṭibb (Generalities on medicine), where (also under the influence of Ibn Bājja) Ibn Rushd discusses the role of philosophy for dealing with scientific materials. However, being less expert than in medicine, his Summary of the Almagest is more an attempt to understand the scope of theoretical astronomy in his time rather than an attempt at an authoritative work such as represented by the Kulliyyāt. Ibn Rushd asks to what extent astronomy can be considered a true science and deals not only with mathematical astronomy but also with the physical representation of the cosmos. He discusses Ptolemy, comparing and contrasting his work to some of the most important Arabic and Andalusian mathematical astronomers who criticized parts of his system but respected its fundamentals. Ibn Rushd's main sources are the Iṣlāḥ al‐Majisṭī (Corrections to the Almagest) of the Andalusian Jābir ibn Aflaḥ, the Kitāb fī hayʾat al‐ʿālam (Book on the configuration of the World) and al‐Shukūkʿalā Baṭlamyūs of the Egyptian Ibn al‐Haytham, and the treatises by the Andalusian Zarqālī on the motion of the fixed stars and on the Sun. Though he seems convinced that astronomy needs to be thoroughly redefined, in the meantime he is obliged to rely upon the questions on which all the astronomers agree. His short commentaries (jawāmiʿ) to Aristotle's works (generally written during the same period of his life) reflect the doubtful opinions expressed in the Mukhtaṣar al‐Majisṭī. Underlying his short commentaries to the De Caelo and Metaphysics is the paradigm of contemporary astronomy even though it contradicts Aristotle. However, Ibn Rushd disagrees with Ptolemy and Islamic astronomers on many points such as the existence of a ninth sphere. To deal with these contradictions, he uses ambiguous explanations such as the metaphor of the “universal animal” (ḥayawān kullī) found in Ptolemy's Planetary Hypothesis, also echoed in Ibn Ṭufayl's RisālatḤayy ibn Yaqẓān, which he uses to pose the problem of the existence of several motions in the planets in different directions.

Ibn Rushd's opinions evolved during the second period of his work, which was characterized by a strict reading of Aristotle, freeing it from the opinions that both Hellenistic and Islamic philosophy had added to it. For this reason, in his long commentaries (tafāsīr) to De Caelo and the Metaphysics in particular, he openly rejects the existence of eccentrics and epicycles insofar as they contradict the necessity of circular and uniform motions around the Earth for the planets. The main problem is that Ibn Rushd is not aware of the astronomical theories formulated by Eudoxus and Callippus that underlie the Aristotelian cosmos and so has great difficulty in understanding Aristotle's texts on this point. Having no time and insufficient knowledge (as he himself confesses) to formulate a new proposal that allows the coexistence in the same model of the apparent planetary motions alongside Aristotelian tenets, he only suggests that planets have a spiral movement that accounts for both daily motion and motion in longitude. This intuitive idea based on the observation of the Sun (also shared by Biṭrūjī) has some precedents in Plato and Theon of Alexandria, but in Ibn Rushd seems to have sprung from a misreading of Aristotle.

Selected References

Carmody, Francis J. (1952). “The Planetary Theory of Ibn Rushd.” Osiris 10: 556–586.

Cruz Hernández, Miguel (1997). Abū l‐Walīd Ibn Rushd (Averroes): Vida, obra, pensamiento e influencia. 2nd ed. Cordova: Caja Provincial de Ahorros.

Daiber, Hans (1999). Bibliography of Islamic Philosophy. 2 vols. Leiden: Brill. (An exhaustive bibliographical repertory, which contains the list of edited works in vol. 1, pp. 449–468, and a most complete bibliography on Ibn Rushd, mainly as a philosopher, in vol. 2, pp. 231–262.)

Endress, Gerhard (1995). “Averroes' De Caelo: Ibn Rushd's Cosmology in his Commentaries on Aristotle's On the Heavens.” Arabic Sciences and Philosophy 5: 9–49.

——— (2003). “Mathematics and Philosophy in Medieval Islam.” In The Enterprise of Science in Islam: New Perspectives, edited by Jan P. Hogendijk and Abdelhamid I. Sabra, pp. 121–176. Cambridge, Massachusetts: MIT Press.

Forcada, Miquel (1999). “La ciencia en Averroes.” In Averroes y los averroísmos: Actas del III Congreso Nacional de Filosofía Medieval, pp. 49–102. Zaragoza: Sociedad de Filosofia Medieval.

Hugonnard‐Roche, H. (1977). “Remarques sur l'évolution doctrinale d'Averroès dans les commentaires au De Caelo: Le problème du mouvement de la terre.” Mélanges de la Casa de Velazquez 13: 103–117.

——— (1985). “L'épitomé du De Caelo d'Aristote par Averroès: Questions de méthode et de doctrine.” Archives d'histoire doctrinale et littéraire du moyen âge 52: 7–39.

Lay, Juliane (1996). “L'Abrégé de l'Almageste: Un inédit d'Averroès en version hebraïque.” Arabic Sciences and Philosophy 6: 23–61.

Sabra, A. I. (1994). “The Andalusian Revolt against Ptolemaic Astronomy: Averroes and al‐Bitrūjī.” In Transformation and Tradition in the Sciences, edited by Everett Mendelsohn, pp. 133–153. Cambridge: Cambridge University Press. (Reprinted in Sabra, Optics, Astronomy and Logic, XV. Aldershot: Ashgate.)

Samsó, Julio (1992). Las ciencias de los antiguos en al‐Andalus. Madrid: Mapfre.

Urvoy, Dominque (1991). Ibn Rushd (Averroes). (Translated by Olivia Stewart. London: Routledge.)