Abū Bakr Muḥammad ibn Yaḥyà ibn aṣ-Ṣā’igh at-Tūjībī ibn Bājja (Arabic: أبو بكر محمد بن يحيى بن الصائغ التجيبي بن باجة), best known by his Latinised name Avempace (//; c. 1085 – 1138), was an Arab Andalusian polymath, whose writings include works regarding astronomy, physics, and music, as well as philosophy, medicine, botany, and poetry.
He was the author of the Kitāb an-Nabāt ("The Book of Plants"), a popular work on botany, which defined the sex of plants. His philosophical theories influenced the work of Ibn Rushd (Averroes) and Albertus Magnus. Most of his writings and books were not completed (or well-organized) due to 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.
Though many of his works have not survived, his theories in astronomy and physics were preserved by Maimonides and Averroes respectively, and influenced later astronomers and physicists in the Islamic civilization and Renaissance Europe, including Galileo Galilei.
Avempace wrote one of the first (argued by some to be the first) commentaries on Aristotle in the western world. While his work on projectile motion was never translated from Arabic to Latin, his views became well known around the western world and to western philosophers, astronomers, and scientists of many disciplines. His works impacted contemporary medieval thought, and later influenced Galileo and his work. Avempace's theories on projectile motion are found in the text known as "Text 71".
Despite diverging from Aristotle's theory of motion, it appears that Avempace largely agrees with Aristotle's ideas on projectile motion. While there is no known account that lay's out Avempace's ideas over this topic, Avempace gives a short explanation in his commentary of Aristotelian Physics book 8. An interesting piece by Avempace on the theory of projectile motion comes from his example involving a magnet and iron filaments. Magnets present a problem with Aristotle's theory on projectile motion because nothing can be seen physically moving the iron. Avempace, however, believes that a magnet is more complicated than one might think. He presents the idea that the magnet actually moves the air which, in return, moves the iron.
The central theory of the mover and the moved can be seen not only in his work in physics, but also in his work in Philosophy.
Ibn Bajja proposed that for every force there is always a reaction force. While he did not specify that these forces be equal, it is considered an early version of the third law of motion which states that for every action there is an equal and opposite reaction.
Avempace was a critic of Ptolemy and he worked on creating a new theory of velocity to replace the one theorized by Aristotle. Two future philosophers supported the theories Avempace created, known as the Avempacean dynamics. These philosophers were Thomas Aquinas, a Catholic priest, and John Duns Scotus. Galileo Gallilei went on and adopted Avempace's formula and said "that the velocity of a given object is the difference of the motive power of that object and the resistance of the medium of motion" in the Pisan dialogue.
Avempace is known to have made contributions to the field of botany in addition to philosophy and the physical sciences. His work, titled Kitab al-nabat (The Book of Plants) is a commentary influenced by the work De Plantis. In this commentary, Avempace discusses the morphology of various plants and attempts to classify them based on their similarities. He also writes about the reproductive nature of plants and their supposed genders based on his observations of palm and fig trees. Kitab al-nabat was written in Arabic and has most recently been translated into Spanish.
Avempace's book Kitāb al-Tajribatayn ‘alā Adwiyah Ibn Wāfid (Book of Experiences on Drugs of Ibn Wafid) is an attempt to classify plants from a pharmacological perspective. It is based the work of pharmacological perspective. It is based the work of Ibn al-Wafid, a physician and Avempace's predecessor, and is said to have influenced the later work of Ibn al-Baitar, a prominent Arab pharmacologist and botanist.
Avempace's work in botany is evident in his political works.
Recently, the web page Webislam, created by Spanish converts to Islam, reported that the score of the Nuba al-Istihlál of Avempace (11th century), arranged by Omar Metiou and Eduardo Paniagua, is very similar to Marcha Granadera (18th century), which 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.