Sextus Empiricus was almost certainly, as his name suggests, a doctor of the empiricist school, which flourished from the third century BCE until at least the third century CE. His dates are very uncertain, but he probably lived and worked, perhaps in Rome, sometime early in the third century CE. He is mentioned as a prominent skeptic in Diogenes Laertius's Lives of the Philosophers (DL) 9.116, written probably in the third century; but the men Diogenes names as his teacher and pupil, Herodotus of Tarsus and Saturninus, are even more obscure. He was certainly known as the authoritative source of skeptical argument a century later, when Saint Gregory of Nazianzus blamed him for the "vile and malignant disease" of arguing both sides of a question that was infecting the church. How original he was is unclear—it is hard to tell...