While many Intro Philosophy classes cover Descartes’ Deceiving Demon thought experiment, few cover Avicenna’s Floating Man thought experiment, which is remarkably similar 600 years earlier.

Avicenna was one of the greatest and most famous philosophers and doctors of his day.  His name, Ibn Sina in Arabic, was Latinized as his works were read by many in Europe before and during the Renaissance and European Enlightenment.  His Canon of Medicine was used as a textbook in Europe until the 1700s, based on experimentation and clinical trials, fusing Persian, Greek, Indian and other traditions of medicine together.  He was also a pioneer of equations and propositional algebra, which would be developed later by Descartes into his Cartesian coordinates and by Newton and Leibniz into Calculus.

In his floating man thought experiment, Avicenna, who worked with anesthetics like opium in public hospitals, asks us to imagine that we are slowly unable to feel our feet, then body, then sight and sensation, then memory and imagination.  What is the last thing left that is ourselves?  Avicenna argues that consciousness, our awareness, is the last thing and the most essential part of ourselves.  If we are conscious, we can be said to exist, even if we forget who we are or cannot distinguish ourselves from anything else.

In his Discourse on Method, Descartes lays out his remarkably similar Deceiving Demon thought experiment.  Descartes says that it seems certain that he is sitting by the fire writing, but he can doubt this and believe that he is simply dreaming.  This is similar to Zhuangzi, the ancient Chinese Daoist, who after dreaming he was a butterfly supposed that he might now be a butterfly dreaming that he is a man named Zhuangzi.

Descartes says that he can imagine a deceiving demon is creating a false world, like a dream, such that Descartes is not actually Descartes or sitting by a fire.  However, there is one thing that the demon cannot be deceiving Descartes about, if that is his real name, and that is his consciousness.  Thus, Descartes famously concludes, “I think therefore I am”.

Where does the deceiving demon of Descartes come from?  The Cathars, Gnostic Manichaean Christians persecuted in France in the 1400s, believed that this world is a lie ruled by Satan, much like the shadows on the wall of Plato’s Cave.  The Catholic Church denounced this as heresy, arguing that God ruled the world and spoke through the Church.  Descartes, the first modern European philosopher, argues that we can trust the dogmas of the Church and the discoveries of science, as our world is not simply a lie as Gnostics claim.  He argues this based on the same conclusion that Avicenna reached, though Avicenna uses anesthetics rather than a demon.  There is a good possibility that Descartes was influenced by Avicenna, though few consider the incredible impact of the Islamic golden age on the European Enlightenment.