Avicenna (Ibn Sīnā)

Abū ʿAlī al-Ḥusayn ibn Sīnā — “Avicenna” in Latin — was born around 980 near Bukhara, in Central Asia, then ruled by the Persian Samanid dynasty. A prodigy, he knew the Quran by heart at ten, mastered logic, mathematics and physics, and was practising medicine at sixteen. When he cured the Samanid prince Nuh ibn Mansur, he was given access to the royal library — “I saw books whose very names are unknown to many” — which burned down soon after (enemies accused him of setting the fire to keep its knowledge for himself).

His life was spent moving between the courts of rival princes in Persia — Gurganj, Rayy, Hamadan, Isfahan — as physician, vizier, sometimes prisoner, writing at night, often on horseback during campaigns, dictating to students. He loved wine and pleasure, and worked prodigiously: some 450 works are attributed to him, about 240 surviving. He died in Hamadan in 1037, reportedly of a colic he treated too aggressively, saying, “The governor who governed my body is unable to govern it any longer.”

The Canon of Medicine

Al-Qānūn fī al-Ṭibb — five books, a million words — systematized Greek (Galen, Hippocrates), Persian and Indian medicine with Avicenna’s own observations. It discusses contagion, quarantine, the testing of drugs (with rules that anticipate clinical trials), anatomy, and psychology. Translated into Latin by Gerard of Cremona in the twelfth century, it remained a standard medical textbook at European universities such as Montpellier and Louvain until the seventeenth century.

The Book of Healing

His philosophical encyclopedia, Kitāb al-Shifāʾ (“The Book of Healing” — of the soul from ignorance), covers logic, natural philosophy, mathematics and metaphysics, reworking Aristotle into a new system. Its shorter companion, al-Najāt (“The Salvation”), and his late al-Ishārāt wa al-Tanbīhāt (“Pointers and Reminders”) were studied for centuries.

Essence and existence

Avicenna’s most influential idea is the distinction between essence and existence. I can understand what a triangle or a phoenix is without knowing whether any exists. So existence is not part of the essence of things — it “happens to” them, is added from outside. Every created thing is possible in itself (mumkin al-wujūd): considered in itself, it could exist or not; it exists only because something causes it to.

The proof of the Necessary Existent

From this follows his proof of God (wājib al-wujūd, the “Necessary of Existence”):

1. Whatever exists is either necessary in itself or possible in itself.
2. A possible being exists only through a cause.
3. The whole series of possible beings — finite or infinite — is itself possible, and needs a cause outside the series.
4. That cause must be necessary in itself.

The Necessary Existent is one, simple, pure intellect, whose essence is its existence. From it, by emanation, flow a series of intellects, the heavenly spheres and finally the world — a Neoplatonic structure grafted onto Aristotle.

The Flying Man

In On the Soul, Avicenna proposes a thought experiment (al-insān al-muʿallaq): imagine a man created fully formed in an instant, suspended in empty air, his sight veiled, his limbs separated so they do not touch, with no sensation at all. Would he affirm his own existence? Yes — he would be aware of his self, though aware of nothing bodily. Therefore the self is something other than the body. Six centuries later René Descartes reached a similar conclusion through doubt; whether Descartes knew of Avicenna’s argument is debated.

Critics and heirs

Avicenna’s synthesis provoked the most famous attack in Islamic philosophy: Al-Ghazālī‘s Incoherence of the Philosophers (c. 1095), which condemned as heresy his doctrines of the eternity of the world, God’s knowledge of particulars only “in a universal way”, and the denial of bodily resurrection. Averroes (Ibn Rushd) defended Aristotle against both. In the Latin West, Avicenna’s metaphysics shaped Albert the Great, Thomas Aquinas (who adopted the essence–existence distinction) and Duns Scotus. In Iran, his tradition continued unbroken through Suhrawardī, Mullā Ṣadrā and beyond.