Ibn Bajjah
Born 1095
Zaragoza, Al-Andalus
Died 1138
Fes, Al-Maghreb
Nationality Andalusian
Fields Astronomer, Philosopher, Physician, Physicist, Poet, Scientist
Abū-Bakr Muhammad ibn Yahya ibn al-Sāyigh (Arabic أبو بكر محمد بن يحيى بن الصائغ), known as Ibn Bājjah (Arabic: ابن باجة‎), was an Andalusian polymath: an astronomer, logician, musician, philosopher, physician, physicist, psychologist, botanist, poet and scientist.[1] He was known in the West by his Latinized name, Avempace. He was born in Zaragoza in what is today Spain and died in Fes, Morocco in 1138. Avempace worked as vizir for Abu Bakr ibn Ibrahim Ibn Tîfilwît, the Almoravid governor of Zaragoza. Avempace also wrote poems (panegyrics and 'muwasshahat') for him, and they both enjoyed music and wine. Avempace joined in poetic competitions with the poet al-Tutili. He later worked, for some twenty years, as the vizir of Yahyà ibn Yûsuf Ibn Tashufin, another brother of the Almoravid Sultan Yusuf Ibn Tashufin (died 1143) in Morocco.[2] He was the famous author of the Kitab al-Nabat (The Book of Plants), a popular work on Botany, which defined the sex of Plants. Among his many teachers was Abu Jafar ibn Harun of Trujillo a physician in Seville, Al-Andalus.

His philosophic ideas had a clear effect on Ibn Rushd and Albertus Magnus. Most of his writings and book were not completed (or well organized) because of his early death. He had a vast knowledge of Medicine, Mathematics and Astronomy. His main contribution to Islamic Philosophy is his idea on Soul Phenomenology, but unfortunately not completed.

His beloved expressions were Gharib غريب and Mutawahhid متوحد, two approved and popular expressions of Islamic Gnostics.

Ibn Bajjah was, in his time, not only a prominent figure of philosophy, but also of music and poetry.[3] His diwan (Arabic: collection of poetry) was rediscovered in 1951.

Though many of his works have not survived, his theories on astronomy and physics were preserved by Maimonides and Averroes respectively, which had a subsequent influence on later astronomers and physicists in the Islamic civilization and Renaissance Europe, including Galileo Galilei.[4]


In Islamic astronomy, Maimonides wrote the following on the planetary model proposed by Ibn Bajjah:

"I have heard that Abu Bakr [Ibn Bajja] discovered a system in which no epicycles occur, but eccentric spheres are not excluded by him. I have not heard it from his pupils; and even if it be correct that he discovered such a system, he has not gained much by it, for eccentricity is likewise contrary to the principles laid down by Aristotle.... I have explained to you that these difficulties do not concern the astronomer, for he does not profess to tell us the existing properties of the spheres, but to suggest, whether correctly or not, a theory in which the motion of the stars and planets is uniform and circular, and in agreement with observation."[5]

In his commentary on Aristotle's Meteorology, Ibn Bajjah presented his own theory on the Milky Way galaxy. Aristotle believed the Milky Way to be caused by "the ignition of the fiery exhalation of some stars which were large, numerous and close together" and that the "ignition takes place in the upper part of the atmosphere, in the region of the world which is continuous with the heavenly motions." On the other hand, Aristotle's Arabic commentator Ibn al-Bitriq considered "the Milky Way to be a phenomenon exclusively of the heavenly spheres, not of the upper part of the atmosphere" and that the "light of those stars makes a visible patch because they are so close." Ibn Bajjah's view differed from both, as he considered "the Milky Way to be a phenomenon both of the spheres above the moon and of the sublunar region." The Stanford Encyclopedia of Philosophy describes his theory and observation on the Milky Way as follows:[6]

"The Milky Way is the light of many stars which almost touch one another. Their light forms a “continuous image” (khayâl muttasil) on the surface of the body which is like a “tent” (takhawwum) under the fierily element and over the air which it covers. Avempace defines the continuous image as the result of refraction (in‛ikâs) and supports its explanation with an observation of a conjunction of two planets, Jupiter and Mars which took place in 500/1106-7. He watched the conjunction and “saw them having an elongate figure” although their figure is circular."

Ibn Bajjah also reported observing "two planets as black spots on the face of the Sun." In the 13th century, the Maragha astronomer Qotb al-Din Shirazi identified this observation as the transit of Venus and Mercury.[7] However, Ibn Bajjah cannot have observed a Venus transit, as there were no Venus transits in his lifetime.[8]


In Islamic physics, Ibn Bajjah's law of motion was equivalent to the principle that uniform motion implies absence of action by a force. This principle would later form the basis of modern mechanics and have a subsequent influence on the classical mechanics of physicists such as Galileo Galilei. Ibn Bajjah's definition of velocity was also equivalent to Galileo's definition of velocity:[9]

Velocity = Motive Power - Material Resistance

where the motive power is measured by the specific gravity of the mobile body and the material resistance is the resisting medium whose resistive power is measured by its specific gravity.[10]

Ibn Bajjah was among the first to state that there is always a reaction force for every force exerted, a precursor to Gottfried Leibniz's idea of force which underlies Newton's third law of motion or law of reciprocal actions.[11]However, the history of the principle of action and reaction can be traced as far as Aristotle.[12]

Ibn Bajjah also had an influence on Thomas Aquinas' analysis of motion. In his Systeme du Monde, the pioneering historian of medieval science, Pierre Duhem, stated:

"For the first time we have seen human reason distinguish two elements in a heavy body: the motive force, that is, in modern terms, the weight; and the moved thing, the corpus quantum, or as we say today, the mass. For the first time we have seen the notion of mass being introduced in mechanics, and being introduced as equivalent to what remains in a body when one has suppressed all forms in order to leave only the prime matter quantified by its determined dimensions. Saint Thomas Aquinas's analysis, completing Ibn Bajjah's, came to distinguish three notions in a falling body: the weight, the mass, and the resistance of the medium, about which physics will reason during the modern era....This mass, this quantified body, resists the motor attempting to transport it from one place to another, stated Thomas Aquinas."[13]

Text 71Edit

Text 71 of Averroes' commentary on Aristotle's Physics contains a discussion on Ibn Bajjah's theory of motion, as well as the following quotation from the seventh book of Ibn Bajjah's lost work on physics:

"And this resistance which is between the plenum and the body which is moved in it, is that between which, and the potency of the void, Aristotle made the proportion in his fourth book; and what is believed to be his opinion, is not so. For the proportion of water to air in density is not as the proportion of the motion of the stone in water to its motion in air; but the proportion of the cohesive power of water to that of air is as the proportion of the retardation occurring to the moved body by reason of the medium in which it is moved, namely water, to the retardation occurring to it when it is moved in air."[14]
"For, if what some people have believed were true, then natural motion would be violent; therefore, if there were no resistance present, how could there be any motion? For it would necessarily be instantaneous. What then shall be said concerning the circular motion? There is no resistance there, because there is no cleavage of a medium involved; the place of the circle is always the same, so that it does not leave one place and enter another; it is therefore necessary that the circular motion should be instantaneous. Yet we observe in it the greatest slowness, as in the case of the fixed stars, and also the greatest speed, as in the case of the diurnal rotation. And this is caused only by the difference in perfection between the mover and the moved. When therefore the mover is of greater perfection, that which is moved by it will be more rapid; and when the mover is of lesser perfection, it will be nearer (in perfection) to that which is moved, and the motion will be slower."[14]

Averroes writes the following comments on Ibn Bajjah's theory of motion:

"Avempace, however, here raises a good question. For he says that it does not follow that the proportion of the motion of one and the same stone in water to its motion in air is as the proportion of the density of water to the density of air, except on the assumption that the motion of the stone takes time only because it is moved in a medium. And if this assumption were true, it would then be the case that no motion would require time except because of something resisting it for the medium seems to impede the thing moved. And if this were so, then the heavenly bodies, which encounter no resistant medium, would be moved instantaneously. And he says that the proportion of the rarity of water to the rarity of air is as the proportion of the retardation occurring to the moved body in water, to the retardation occurring to it in air."[15]
"And if this which he has said be conceded, then Aristotle's demonstration will be false; because, if the proportion of the rarity of one medium to the rarity of the other is as the proportion of accidental retardation of the movement in one of them to the retardation occurring to it in the other, and is not as the proportion of the motion itself, it will not follow that what is moved in a void would be moved in an instant; because in that case there would be subtracted from the motion only the retardation affecting it by reason of the medium, and its natural motion would remain. And every motion involves time; therefore what is moved in a void is necessarily moved in time and with a divisible motion; and nothing impossible will follow. This, then, is Avempace's question."[16]


In Islamic psychology, Ibn Bajjah "based his psychological studies on physics." In his essay, Recognition of the Active Intelligence, he wrote that active intelligence is the most important ability of human beings, and he wrote many other essays on sensations and imaginations. He concluded that "knowledge cannot be acquired by senses alone but by Active Intelligence, which is the governing intelligence of nature." He begins his discussion of the soul with the definition that "bodies are composed of matter and form and intelligence is the most important part of man—sound knowledge is obtained through intelligence, which alone enables one to attain prosperity and build character." He viewed the unity of the rational soul as the principle of the individual identity, and that by its contact with the Active Intelligence, it "becomes one of those lights that gives glory to God." His definition of freedom is "that when one can think and act rationally". He also writes that "the aim of life should be to seek spiritual knowledge and make contact with Active Intelligence and thus with the Divine."[17]


Recently, the web page Webislam of Spanish converts to Islam, reported that the score of the Nuba al-Istihlál of Avempace (11th century), arranged by Omar Metiou and Eduardo Paniagua, save almost complete similarity with Marcha Granadera (18th century) is now the official anthem of Spain. What makes it the world's oldest song (about a thousand years old) used for the official anthem of a country.[18]


  1. Jon Mcginnis, Classical Arabic Philosophy: An Anthology of Sources, p. 266, Hackett Publishing Company, ISBN 0872208710.
  2. Vincent Lagardère, 1989, pp. 80 and 174-178)
  3. D. M. Dunlop, "The Dīwān Attributed to Ibn Bājjah (Avempace)", Bulletin of the School of Oriental and African Studies, University of London Vol. 14, No. 3, Studies Presented to Vladimir Minorsky by His Colleagues and Friends (1952), pp. 463
  4. Ernest A. Moody (April 1951). "Galileo and Avempace: The Dynamics of the Leaning Tower Experiment (I)", Journal of the History of Ideas 12 (2), p. 163-193.
  5. Bernard R. Goldstein (March 1972). "Theory and Observation in Medieval Astronomy", Isis 63 (1), p. 39-47 [40-41].
  6. Josep Puig Montada (September 28, 2007). "Ibn Bajja". Stanford Encyclopedia of Philosophy. Retrieved on 2008-07-11.
  7. Template:Title=History of oriental astronomy: proceedings of the joint discussion-17 at the 23rd General Assembly of the International Astronomical Union, organised by the Commission 41 (History of Astronomy), held in Kyoto, August 25–26, 1997
  8. Fred Espenak, Six Millennium Catalog of Venus Transits
  9. Ernest A. Moody (June 1951). "Galileo and Avempace: The Dynamics of the Leaning Tower Experiment (II)", Journal of the History of Ideas 12 (3), p. 375-422 [379].
  10. Ernest A. Moody (April 1951). "Galileo and Avempace: The Dynamics of the Leaning Tower Experiment (I)", Journal of the History of Ideas 12 (2), p. 163-193 [172-173].
  11. Shlomo Pines (1964), "La dynamique d’Ibn Bajja", in Mélanges Alexandre Koyré, I, 442-468 [462, 468], Paris.
    (cf. Abel B. Franco (October 2003). "Avempace, Projectile Motion, and Impetus Theory", Journal of the History of Ideas 64 (4), p. 521-546 [543].)
  12. Action and Reaction before Newton ,John L. Russell The British Journal for the History of Science, Vol. 9, No. 1 (Mar., 1976), pp. 25-38
  13. See Duhem's analysis of this development - St Thomas Aquinas and the Concept of Mass- on p378-9 of Roger Ariew's 1985 Medieval Cosmology, an extract also to be found online at <>. But Duhem notably fails to accord Averroes his originating innovatory due compared with Avempace and Aquinas, as more clearly accorded by Sorabji's 1988 Matter, Space and Motion p284. Duhem was originally refuting Mach's claim in his Science of Mechanics that Newton first discovered the crucial notion of inertial resistant mass in the 17th century. Mach's error was surprisingly still repeated by the self-professed 'Duhemian gradualist' Bernard Cohen a century later in his 2002 The Cambridge Companion to Newton article Newton's concepts of force and mass, p59.
  14. 14.0 14.1 Ernest A. Moody (April 1951). "Galileo and Avempace: The Dynamics of the Leaning Tower Experiment (I)", Journal of the History of Ideas 12 (2), p. 163-193 [185].
  15. Ernest A. Moody (April 1951). "Galileo and Avempace: The Dynamics of the Leaning Tower Experiment (I)", Journal of the History of Ideas 12 (2), p. 163-193 [184-185].
  16. Ernest A. Moody (April 1951). "Galileo and Avempace: The Dynamics of the Leaning Tower Experiment (I)", Journal of the History of Ideas 12 (2), p. 163-193 [185-186].
  17. (Haque 2004, p. 368)
  18. Redacción de Webislam, «El himno nacional, ¿de origen andalusí?», Número 189, 8 de octubre de 2002. (URL visitada el 13 de marzo de 2007); Actualización: 19 de agosto de 2007.. Grabación sonora de la Nuba al-Istihlál [1]


  • Haque, Amber (2004), "Psychology from Islamic Perspective: Contributions of Early Muslim Scholars and Challenges to Contemporary Muslim Psychologists", Journal of Religion and Health 43 (4): 357–377
  • Marcinkowski, M. Ismail (April 2002), "A Biographical Note on Ibn Bajjah (Avempace) and an English Translation of his Annotations to al-Farabi's Isagoge", in Iqbal Review (Lahore, Pakistan), vol. 43, no. 2, pp. 83–99.
  • The Diwan Attributed to Ibn Bajjah (Avempace),D. M. Dunlop, Bulletin of the School of Oriental and African Studies, University of London, Vol. 14, No. 3, Studies Presented to Vladimir Minorsky by His Colleagues and Friends (1952), pp. 463–477
  • Miquel Forcada (2005). "Ibn Bajja". Medieval Science, Technology, and Medicine: An Encyclopedia. Ed. Thomas F. Glick, Steven John Livesey, and Faith Wallis. Routledge. 243–246. ISBN 0415969301. 

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