Avicenna (Ibn Sina)

Abu Ali al-Husayn ibn Abd Allah ibn Sina, known in Europe as Avicenna, was a Persian philosopher and physician of the late tenth and early eleventh centuries. He built the most complete and influential philosophical system of the medieval Islamic world, reshaping Aristotle's legacy with original ideas about existence, God and the soul, and he wrote the Canon of Medicine, which served as a standard medical textbook in the Islamic world and in European universities for some five hundred years.

Avicenna was born around 980 in Afshana, a village near Bukhara in today's Uzbekistan. His father, originally from Balkh, was an official of the Samanid Empire, whose capital Bukhara was a major centre of Persian and Arabic learning. Much of what is known of his life comes from a short autobiography, continued after his death by his student Abu Ubayd al-Juzjani.

By his own account he was a prodigy. He knew the Quran and much Arabic literature by ten, then studied arithmetic, Islamic law, logic, geometry and astronomy, quickly outpacing his teachers. He took up medicine at about sixteen and found it easy, treating patients while still a teenager. Aristotle's Metaphysics baffled him, he wrote, though he read it forty times, until he found a cheap copy of a short commentary by Al-Farabi that explained its purpose. When he was about seventeen he helped cure the Samanid ruler Nuh II ibn Mansur and was allowed to use the royal library, where he read books he never saw again.

The Samanid state collapsed around 999, and his father died at about the same time. Avicenna spent the rest of his life moving between the courts of rulers in Central Asia and Iran, at a time of rapid political change. He worked for a time at Gurganj in Khwarazm, then left, according to later stories to avoid a summons to the court of Mahmud of Ghazni, ruler of the expanding Ghaznavid Empire. He moved on to Jurjan, where al-Juzjani became his pupil, and to Rayy.

In Hamadan he served the Buyid prince Shams al-Dawla as physician and twice as vizier, a position that drew him into court politics; troops once mutinied and demanded his death. After the prince's death he was suspected of corresponding with a rival ruler and was imprisoned for several months in the fortress of Fardajan, where he kept writing. He escaped to Isfahan, where the Kakuyid ruler Ala al-Dawla gave him the most settled years of his life, from about 1024. He accompanied his patron on campaigns, and on one of them, in June 1037, he died of an intestinal illness at Hamadan in today's Iran, where his tomb still stands. Al-Juzjani says he worked by day, taught and wrote at night, and enjoyed wine and other pleasures, which he did not hide.

Around 450 works are attributed to Avicenna, of which some 240 survive, most in Arabic and a few in Persian. His great philosophical encyclopedia, the Kitab al-Shifa, "The Book of the Cure" (meaning the cure of the soul from ignorance), covers logic, natural science, mathematics and metaphysics. Shorter versions include the Kitab al-Najat, "The Book of Salvation", and his late work al-Isharat wal-Tanbihat, "Pointers and Reminders". He also wrote the Danishnama-yi Alai, one of the first philosophical works in Persian.

He worked within the tradition of Aristotle but changed it deeply. His most important idea was the distinction between essence and existence. What a thing is, its essence, does not include the fact that it exists; we can understand what a horse is without knowing whether any horse exists. So the existence of every ordinary thing must come from a cause. Such things are "possible in themselves". A chain of such causes cannot explain itself, so there must be a being whose essence simply is to exist: the Necessary Existent, which he identified with God. This argument, independent of Aristotle's proof from motion, became one of the classic proofs of God's existence.

Like al-Farabi, he held that the world emanates eternally from God through a series of intellects, the last of which, the Active Intellect, gives forms to matter and knowledge to human minds. He held that the world is eternal and that God knows particular things only "in a universal way", positions later attacked as unorthodox.

Avicenna argued that the human soul is an immaterial substance, not dependent on the body, and therefore survives death. To illustrate this he proposed a famous thought experiment, the "floating man". Imagine a person created fully formed, suspended in the air, blindfolded, with limbs apart so that they touch nothing and feel nothing. Such a person, he argued, would still be aware that they exist, even with no awareness of having a body, so the self is something other than the body. The argument has often been compared with the later reasoning of René Descartes.

Avicenna's medical masterpiece, al-Qanun fi al-Tibb, "The Canon of Medicine", was largely completed in the 1020s. It brought together Greek medicine, above all the work of Galen and the tradition of Hippocrates, with Persian, Indian and Arabic medical knowledge and his own clinical experience, and organised it into a single logical system. It is divided into five books. The first sets out general principles: the four humours and temperaments, anatomy, the causes and signs of disease, hygiene and the general methods of treatment. The second is a pharmacopoeia of several hundred simple drugs, arranged alphabetically. The third covers diseases of particular parts of the body, from head to foot. The fourth deals with conditions that affect the whole body, such as fevers, as well as wounds, fractures and poisons. The fifth describes compound medicines.

The Canon was notable for its clear organisation and for points such as its discussion of contagious diseases, its description of many conditions, and a set of rules for testing new drugs, including testing on the human body and checking results through repeated trials. Its framework remained the humoral medicine of Galen, which was later abandoned. Translated into Latin by Gerard of Cremona in the twelfth century, it became a core text of medical teaching in Europe, printed many times after 1473 and used at universities such as Montpellier and Leuven into the seventeenth century. In the Islamic world it remained authoritative even longer.

Avicenna's philosophy dominated later thought in the Muslim world so thoroughly that later thinkers were often defined by their response to him. The theologian Al-Ghazali attacked his views on the eternity of the world, God's knowledge and bodily resurrection in The Incoherence of the Philosophers, and Averroes later criticised him for straying from Aristotle. Yet his ideas were absorbed into Islamic theology and remained central in Iran for centuries. In Latin translation he deeply influenced medieval Christian thinkers, including Thomas Aquinas, especially through his distinction between essence and existence. He is a central figure of Islamic philosophy and of the Islamic Golden Age, and Iran, Uzbekistan, Tajikistan and Afghanistan all honour him as a national figure.