Chrysippus, the Stoic philosopher born at Soli, in Cilicia, became the third leader of the Stoa at Athens upon the death of Cleanthes, in 232 BCE. This post he held until his own death. Because of his defense of the Stoa against the attacks of Arcesilaus and the skeptical Academy, and undoubtedly also on the basis of his voluminous writings, it was said in antiquity "if there had been no Chrysippus, there would be no Stoa." He wrote 705 books, about half of which, judging from the catalog preserved by Diogenes Laertius, dealt with logic and language. None of his works is extant, though quotations from his books and assessments of some of his views have survived in the works of other ancient authors.

Chrysippus's epistemology is empirical. Presentations of objects are produced in the ruling part of the soul by movements engendered in...