Chrysippus, a native of Soli in Cilicia, became the third head of the Stoa, after Zeno and Cleanthes, in 230 BC. His position within the School was sans pareil—thus the quip Were there no Chrysippus, there would be no Stoa (Diog. Laert. 7.183). With an oeuvre of over seven hundred books, he was also one of the most prolific authors antiquity had seen. What remains are a few hundred snippets of text: a handful of papyri—notably of his Logical Investigations (PHerc. 307; cf. FDS 698)—, a few dozen quotations, and many reports of mostly much later sources which in general are hostile or incompetent or both. There are, in addition, a few thousand anonymous fragments—pieces attributed to the Stoics in general. Scholars ascribe many of them to Chrysippus, too. Though in theory this seems the right thing to do, in practice the selection is often exceptionally difficult. As a result of these uncertainties, the different reconstructions of Chrysippus’ system vary greatly one from another.

Philosophy, according to Chrysippus, divides into three species: logic [λογική] studies λόγοс, that is, both language and reason; physics investigates the world; and ethics examines how one can live in accordance with the world (Diog. Laert. 7.39). Logic divides into the two sciences of dialectic and rhetoric (7.41). Dialectic, in turn, subdivides into a part concerned with sound [φωνή], and a part dedicated to the items signified [сημαινόμενα] (7.43). In a diagram:

         Physics         Logic         Ethics
                               Dialectic    Rhetoric
  Science of sound  Science of what is signified

The study of dialectic is indispensable to one’s success in life—even the Wise Man, that elusive creature, is a dialectician (7.83): for otherwise he would not be infallible in argument (7.47).

(To read on, see my paper The Birth of Grammar on Greece.)