the literary history of the ancients, that branch of logic which taught the rules and modes of reasoning. See Logic, Part III.

Zeno Eleates was the first who discovered the natural series of principles and conclusions observed in reasoning, and formed an art thereof in form of a dialogue; which, for this reason, was called dialektica.

The dialectica of the ancients is usually divided into several kinds: the first was the eleatic, that of Zeno Eleates, which was threefold: viz., vonfocutionum, colloquationum, and contentionum. The first consisting of rules for deducing or drawing conclusions. The second, the art of dialogue; which became of such universal use in philosophy, that all reasoning was called interrogation: then, syllogism being laid aside, the philosophers did all by dialogue; it lying on the respondent to conclude and argue from the several conceivings made. The last part of Zeno's dialectics, Epius, was contentious, or the art of disputing and contradicting; though some, particularly Laertius, ascribe this part to Protagoras a disciple of Zeno.

The second is the dialektica megarica, whose author is Euclid, not the mathematician, but another of Megara. He gave much into the method of Zeno and Protagoras; though there are two things appropriated to him: the first, that he impugned the demonstrations of others, not by assumptions, but conclusions; continually making illations, and proceeding from consequence to consequence: the second, that he set aside all arguments drawn from comparisons of similitude as invalid.

He was succeeded by Eubulides, from whom the sophistical way of reasoning is said to be derived. In his time the art is described as manifold: mentions, fallens, electra, obvelata, arcevalis, cornuta, and calva. See Sophism.

The third is the dialektica of Plato, which he proposes as a kind of analysis to direct the human mind, by dividing, defining, and bringing things to the first truth; where being arrived, and stopping there a little, it applies itself to explain sensible things, but with a view to return to the first truth, where alone it can rest. Such is the idea of Plato's analysis.

The fourth is Aristotle's dialectics; containing the doctrine of simple words, delivered in his book of Predicaments; the doctrine of propositions, in his book De Interpretationes; and that of the several kinds of syllogism, in his books of Analytics, Topics, and Elenchus.

The fifth is the dialectics of the Stoics; which they call a part of philosophy, and divide into rhetoric and dialectic; to which some add the definitive, whereby things are justly defined; comprehending likewise the canons or criterions of truth.

The Stoics, before they come to treat of syllogisms, have two principal places; the one about the signification of words, the other about the things signified. On occasion of the first, they consider abundance of things belonging to the grammarian's province: what, and how many letters; what is a word, diction, speech, &c. On occasion of the latter, they consider things themselves, not as without the mind, but as in it, received in it by means of the senses. Accordingly, they first teach, that nil fit in intellectu, quod non prius fuerit in sensu; "whatever is in the mind came thither by the senses;" and that aut incuriosae sunt, as Plato, who meets the sight; aut similitudine, as Caesar by his effigy; aut proportione, either by enlarging as a giant or by diminishing as a pygmy; aut translatione, as a Cyclops; aut compositione, as a Centaur; aut contrario, as death; aut privatione, as a blind man.

The sixth is Epicurus's dialectics; for though he seems to have despised dialectic, he cultivated it with vigour. He was only adverse to that of the Stoics; who he thought attributed too much to it, as pronouncing him alone wise who was well versed in dialectics. For this reason, Epicurus, seeming to set aside the common dialectics, had recourse to another way; viz., to certain canons which he substituted in their stead, the collection whereof he called canonica; and as all questions in philosophy are either de re or de voce, he gave separate rules for each. See Epicureans.