Philosophy › Faith and reason › Philosophy in the Islamic world (falsafa)
Avicenna (Ibn Sina)
980–1037· Philosopher· Reality, mind & God
Well documentedSolid records, texts or physical evidence.
Persian polymath, the most influential philosopher of the Islamic world, whose medical textbook was used for some 600 years.
See it on the Philosophy map →The idea
Idea: what a thing is (essence) differs from whether it is (existence), so anything that might not have existed needs a cause, ending in a Necessary Being, God. Born near Bukhara (now Uzbekistan), Ibn Sina served Persian rulers as physician and vizier. He wrote The Book of Healing (al-Shifa), an encyclopedia of philosophy and science, and The Canon of Medicine. His 'flying man' thought experiment argued the self knows itself without the body. Main objection: al-Ghazali said his God was not scripture's God.
Why it matters
His essence–existence distinction and contingency argument shaped Aquinas and Scholasticism; the Canon remained a standard medical text in Europe into the 1600s.
Legacy and sources
His works survive in Arabic and medieval Latin; his autobiography, completed by his student al-Juzjani, is the main source on his life.
Still debated
Whether his late 'Eastern philosophy' marked a real break from Aristotle or was mostly a label is debated.
Connections (4)
▸Avicenna (Ibn Sina) was attacked by Al-Ghazali, The Incoherence of the PhilosophersWell documented
The connection
Avicenna had built Aristotle into a grand system: an eternal world flowing necessarily from God, a God who knows things only in general, and a soul that survives without the body. Al-Ghazali first summarized this system accurately, then refuted it on twenty points in The Incoherence of the Philosophers, branding three of them unbelief.
When and how
Baghdad, about 1094–1095, while al-Ghazali taught at the Nizamiyya college, some 60 years after Avicenna's death.
How we know
The Incoherence names al-Farabi and Avicenna as its main targets, and its arguments track Avicenna's works, which al-Ghazali had summarized in The Aims of the Philosophers.
Debates and open questions
Scholars debate how much al-Ghazali quietly absorbed from Avicenna; his later theology uses many Avicennan ideas.
▸Avicenna (Ibn Sina) gave the contingency argument to Does God exist?Mostly agreed
The connection
Avicenna argued that anything whose existence is merely possible needs a cause outside itself. A chain of possible things, even an infinite one, is as a whole still merely possible, so there must be a Necessary Existent, whose essence is to exist. That is God.
When and how
Persia, early 11th century, in The Book of Healing and The Book of Salvation (al-Najat).
How sure are we?
The argument is set out in his surviving works; Aquinas' third way and Leibniz's contingency argument closely follow its pattern.
Debates and open questions
Whether a necessary existent is the personal God of religion, as al-Ghazali doubted, and whether a whole chain needs an outside cause, are disputed.
▸Avicenna (Ibn Sina) influenced Thomas AquinasWell documented
The connection
Avicenna's distinction between a thing's essence (what it is) and its existence (that it is) became central for Aquinas, who argued that only in God are essence and existence identical. Avicenna's argument from contingent and necessary being also shaped Aquinas's Third Way, and his theory of the soul informed Aquinas's psychology.
When and how
Avicenna's Metaphysics and On the Soul reached Latin in Toledo around 1150–1180; Aquinas used them in Paris from the 1250s, notably in On Being and Essence.
How we know
Aquinas cites Avicenna by name frequently, and his early treatise On Being and Essence (c. 1255) relies on him openly.
Debates and open questions
Scholars debate whether Aquinas's idea of existence as an act truly comes from Avicenna or is his own original turn.
▸Avicenna (Ibn Sina) anticipated, with his "flying man," Mind–body dualismMostly agreed
The connection
Avicenna imagined a man created in midair, blindfolded, limbs apart, touching nothing. He would still know he exists without knowing he has a body, so the self or soul must be distinct from the body. Descartes' argument that he can doubt his body but not his mind follows a strikingly similar path.
When and how
Avicenna's Book of Healing (al-Shifa), the part On the Soul, written in Persia in the 1020s; translated into Latin in Toledo in the 12th century.
How sure are we?
The 'flying man' was widely known to medieval Latin scholars through that translation; its parallel with Descartes' Meditations is a standard point in histories of philosophy.
Debates and open questions
Whether Descartes knew the argument, directly or through scholastic teaching at his Jesuit school, is unproven, and the two arguments serve different purposes.