He was the author of the Kitab al-Nabat (“The Book of Plants”), a popular work on botany, which defined the sex of plants. His philosophic ideas had a clear effect on Ibn Rushd (Averroes) 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 was his idea on soul phenomenology, which was never completed.
Avempace was, in his time, not only a prominent figure of philosophy, but also of music and poetry. 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 influenced later astronomers and physicists in the Islamic civilization and Renaissance Europe, including Galileo Galilei.
The Ibn Bajja crater on the Moon is named in his honor.
Avempace was born in Zaragoza in what is today Aragon, Spain, around 1085 and died in Fes, Morocco, in 1138. He worked as vizir for Abu Bakr ibn Ibrahim Ibn Tîfilwît, the Almoravid governor of Zaragoza. Avempace also wrote poems (panegyrics and muwasshahat) for him. 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. Among his many teachers was Abu Jafar ibn Harun of Trujillo a physician in Seville, Al-Andalus.
“I have heard that Abu Bakr 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.”
In his commentary on Aristotle’s Meteorology, Avempace 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.” Avempace’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:
“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.”
Avempace 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. However, Avempace cannot have observed a Venus transit, as there were no Venus transits in his lifetime.
Text 71 of Averroes‘ commentary on Aristotle‘s Physics contains a discussion on Avempace’s theory of motion, as well as the following quotation from the seventh book of Avempace’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.”
“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.”
Averroes writes the following comments on Avempace’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.”
“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.”
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. That makes it the world’s oldest song (about a thousand years old) used for the official anthem of a country.