Cleanthes (sometimes referred to as Cleanthes of Assos) was the second head of the Stoic school. Ancient biographical information is found in Diogenes Laërtius's Lives of the Philosophers (7. 168-176) and in Philodemus's history of Stoicism (columns 18-19). Born in 331–330 BCE, in Asia Minor, he came to Athens in 281–280. He took over leadership of the school on the death of its founder, Zeno of Citium, in 262–261 and held that position until his own death in 230–229. The most important contemporary Stoic was Ariston of Chios, against whom Cleanthes defended the version of Zeno's legacy that became standard, insisting on the vital importance of logic and physics as well as ethics. His own student and successor, Chrysippus, maintained this integrated system. Cleanthes also defended Stoic epistemology against the skepticism of the academic Arcesilaus.

Cleanthes was a...