Suspended in a pitch-black void with no sight, sound, or sensation, would you still know that you exist? That sensory deprivation thought experiment, known as the floating man, was devised in the eleventh century by Ibn Sina, the Persian polymath known in the West as Avicenna. This episode traces his life from a prodigious childhood near Bukhara, where he memorized the Quran by ten and learned Hindu-Arabic numerals from an Indian greengrocer, to becoming physician to the Samanid ruler at seventeen and a political refugee when that empire collapsed around 999 CE.

We follow him from court to court, including a grueling journey to Gorgan only to find the ruler had died, his forced service as vizier under Shams al-Dawla, his months in hiding writing fifty pages a day of The Book of Healing, and his four-month imprisonment in a fortress. Along the way we unpack The Canon of Medicine, which remained a European textbook into the 1650s, his early ideas about contagion and quarantine, his theories on the speed of light and rainbows, his rejection of astrology and alchemy, and the proof of the truthful, his logical argument for a necessary existent.

• Why learning arithmetic from a greengrocer meant access to a revolutionary number system including zero
• How medical skill repeatedly saved his life and repeatedly dragged him into dangerous politics
• The domino chain of contingent existence and the finger that flicked the first domino
• The floating man argument for the soul as an immaterial substance distinct from the body
• Al-Ghazali’s later critique of fitting God into Aristotelian boxes, and Avicenna’s death on campaign in 1037 around age fifty-seven