The Islamic world · 980–1037
Ibn Sīnā (Avicenna)
Persian physician-philosopher, the most influential Islamic philosopher
Essence and existence are distinct: knowing what a thing is does not tell you that it is, so all contingent things need a Necessary Existent. His “floating man”, suspended without any sensation, still knows that he exists.
Life and thought
Ibn Sīnā, known in Latin as Avicenna, was born in 980 near Bukhara, in Central Asia. A prodigy, he had mastered medicine by his late teens and was rewarded with the run of the Samanid royal library. When that dynasty fell he moved from court to court across Iran, serving as physician and sometimes vizier, writing at night and on campaigns, and once in prison. He died in Hamadan in 1037.
His Canon of Medicine was taught in Europe for five centuries, and his Book of Healing was an encyclopedia of philosophy. Its central idea is the distinction between essence and existence: you can understand what a triangle or a horse is without knowing whether any exists, so existence is not part of a thing’s essence. Everything whose existence is merely possible must get it from something else, and the chain must end in a Necessary Existent, whose essence is to exist: God. His “floating man”, created in mid-air with no sensations, would still know that he exists, so the soul knows itself directly.