Avicenna was a medieval Islamic philosopher, theologian, and physician born in Persia in 980 CE. As a philosopher, he tried to reconcile Aristotelian and Neoplatonic philosophy with an understanding of Islamic theology and the Quran. Like the Neoplatonists, he believed that the world came forth from God in what is known as the theory of emanation, but he would draw a clear distinction between God as Creator and the World as his Creation in order to maintain the monotheism of Islam. Also like the Neoplatonists, he considered evil to be simply the absence of good. His interest in Aristotle led him to regard sensory experience and experimentation highly, as well as the value of logic. He famously puts forth an argument for the existence of God as the First Cause, as well as his “Floating Man” argument for the existence of the soul as distinct from the body. He is considered the most important philosopher in the Islamic tradition.

As a polymath, Avicenna tried to learn as much as possible. He had an excellent intelligence and memory, and is said to have memorized the entire Quran by the age of 10. He learned mathematics, philosophy and medicine. He became particularly interested in Aristotle, who he was able to understand through the lens of al-Farabi, an earlier Islamic philosopher. At the age of 18, he became a doctor, explaining “Medicine is no hard and thorny science, like mathematics and metaphysics.” While his most famous philosophical work The Cure (al-Shifa) would deeply impact medieval philosophers such as Thomas Aquinas, his most famous medical text the Canon of Medicine (Qanun) would become a standard medical textbook throughout Europe and the Islamic World.

Avicenna famously argues for the existence of God as the First Cause. He explains that because things in the world come and go, they are therefore not necessary. Since they are not necessary, there existence must depend on something that is necessary. This necessary being would be God. God is the First Cause, also known as the Uncaused Cause, whose necessary existence makes possible the “contingent” existence of everything else.

Avicenna will also distinguish between a thing’s essence and it’s existence. A thing’s essence is that which makes it what it is, which is independent of whether it exists or not. For example, a table has four legs and a base regardless of whether an individual table actually exists. Existence refers to there actually being a table or not. For Avicenna, it is only because of God’s necessary existence that everything else is possible to exist. Furthermore, Avicenna believes that God knows things not as individual existing entities, but rather through their essences. God knows the nature of all things, whether a person, an animal, or a material thing. The Islamic philosopher al-Ghazali will critique Avicenna on this point for limiting God’s omniscience (“knowledge of everything.”)

Like the Neoplatonists, Avicenna believes that from God’s Necessary being flows forth the rest of reality. This is known as the theory of emanation. The theory of emanation can be used to support the belief that God and the world are one, known as pantheism, but since Avicenna was trying to reconcile philosophy with the Quran and Islamic culture, he insisted on the distinctiveness of the world from its divine source. In separating Creation from Creator, he was able to maintain a traditional Islamic theological position.

Avicenna believed people can choose either to act according to their divine nature, or not. He believes that through the intellect, we can come to understand the nature of things. He believes that through intuition, we are able to access what he calls the Active Intellect, which allows us to understand the essences of things. Deeply influenced by Aristotle, he believed that through logic one is able to purify the soul in order to be able to more clearly have such insights. In contrast, those who commit evil are not listening to the Active Intellect and are therefore not following God’s will. Evil is therefore seen as the absence of good.

Avicenna also puts forth what is known as his “Flying Man” argument. He explains that if someone was born and suspended in the air, both blind and without the ability to use any of the other senses, they would still be able to tell that they existed because they would have consciousness. For this reason, Avicenna believes that the soul is distinct from the body and that it will also live on after the death of the body. The Flying Man argument will be revisited by Descartes in the modern period, when he says “I think, therefore I am.”

Avicenna’s interest in metaphysics (the nature of reality), logic (the structure of arguments), philosophy and religion represents one aspect of his thoughts. The other aspect is his practical interests in medicine and science. He believed in the importance of scientific experiments and is a precursor to the modern understanding of motion in physics. In medicine, he would advocate a healthy lifestyle including proper diet and exercise. He explains that such proactive measures are better in the long run for the person than simply taking medication. In his personal life, however, he would come to be attacked by future Islamic philosophers for enjoying wine and slave-girls. He explained, “I prefer a short life with width to a narrow one with length,” although on his death bed he would repent, give away his money to charity, and free his slaves.

Avicenna is celebrated for supporting Islamic theology with logic and philosophical reasoning. His work The Cure would come to deeply influence Medieval Christian philosophers such as Thomas Aquinas, known as the Scholastics, who sought to reconcile faith and reason, as well as would become part of the curriculum in the Islamic schools known as madrasas. His medical work the Canon of Medicine is recognized as one of the most important medical works of all time. For both his understanding of philosophy, the Quran and Islam, and medicine, he is celebrated in Iran as a national hero and is considered one of the greatest Persian thinkers of all time.