Lives and Opinions of Eminent Philosophers

​They compare philosophy to a living creature, likening the logical part to bones and sinews, the ethical to the fleshiest parts, and the physical to the soul. Or again to an egg: for the outer parts are logic, the parts after these ethics, and the innermost parts physics. Or to a fertile orchard: where the surrounding hedge is logic, the fruit ethics, and the earth or the trees physics. Or to a city well-walled and governed according to reason. And no part is separated from the other, as some of them say, but they are mixed together; and they used to make the transmission of them mixed. But others arrange logic first, physics second, and ethics third; among whom are Zeno in On Reason, Chrysippus, Archedemus, and Eudromus.

​For Diogenes of Ptolemais begins with ethics, while Apollodorus places ethics second, and Panaetius and Posidonius begin with physics, as Phanias, the acquaintance of Posidonius, states in the first book of Posidonian Lectures. But Cleanthes says there are six parts: dialectic, rhetoric, ethics, politics, physics, and theology. Others say that these are not parts of discourse, but of philosophy itself, as Zeno of Tarsus does. Some say that the logical part is divided into two sciences, into rhetoric and into dialectic; and some also into the definitional species, which concerns canons and criteria; but some remove the definitional part altogether.

​Now, they take up the study of canons and criteria for the sake of discovering the truth; for in it they rectify the differences among impressions. And similarly, they take up the definitional part for the recognition of truth; for through concepts things are grasped. They also hold rhetoric to be the science of speaking well concerning discourses in continuous exposition, and dialectic that of conversing correctly concerning discourses in question and answer; whence they also define it thus, as the science of things true, false, and neither. And they say that rhetoric itself is tripartite; for one part of it is deliberative, another forensic, and another epideictic.

​And its division is into invention, style, arrangement, and delivery; and the rhetorical speech is divided into the prologue, the narrative, the arguments against opponents, and the epilogue. Dialectic is divided into the topic concerning things signified and that of the voice; and that of things signified is divided into the topic concerning impressions and the sayables (lekta) subsisting from them—propositions, complete expressions, predicates, and the like active and passive forms, as well as genera and species—and similarly into arguments, modes, syllogisms, and sophisms arising from voice and from things;

​among which are "the Liar" arguments, truth-telling ones, denying ones, sorites and those similar to these, defective ones, unresolvable ones, conclusive ones, "the Veiled", "the Horned", "the Nobody", and "the Reaper". And dialectic also has as a proper topic the aforementioned one concerning the voice itself, in which is shown what articulate voice is, and what the parts of speech are, and concerning solecism, barbarism, poems, ambiguities, melodious voice, music, and, according to some, definitions, divisions, and diction.