Dialectics and dialogue have the same Greek etymology dia- + legein, dia- “through”, legein “say”. The prefix dia- is different from the prefix di– meaning “two”. Etymologically, a dialogue is not a two-person conversation (which could be referred to as a dilogue). The condition is not on the number of participants, but on discourse circulation. However, the historical notion of dialectic does refer to a two-partner dialogue.
1. The ancient dialectical method
Aristotelian dialectic is a dialogical method used to solve questions of the form “P or not P?”, such as “is being rich a good thing or not?”, by eliminating one of the options, in a standardized question-answer interaction using dialectical syllogisms.
Dialectic is a philosophical instrument used in the a priori search for the definition of fundamental concepts. In this function of clarification of the first principles, it has been replaced by axiomatization.
1.1 Dialectical reasoning
As “mathematical science” and “rhetorical argument”, “dialectical reasoning” proceeds by syllogism and induction (Aristotle, Post. An., I, 1). While scientific syllogistic deduction proceeds from “true and primary” premises, dialectic uses generally accepted premises (Top. I, 1), or simple “opinions”, endoxon:
Our treatise proposes to find a line of inquiry whereby we shall be able to reason from opinions that are generally accepted about every problem propounded to us, and also shall ourselves, when standing up to an argument, avoid saying anything that will obstruct us. (Ibid.)
The word endoxa translates as “probable premises” or as “accepted ideas”. The strict deduction rules of the syllogism are replaced by argument schemes.
1.2 Dialectical game
The dialectical game is played by two partners, the Respondent and the Questioner (Brunschwig 1967, p. 29). It is a bounded interaction governed by strict rules, proceeding by questions and answers, with a winner and a loser. The Respondent first chooses to assert either P or not P. The Questioner must refute the proposition that the Respondent has chosen to support, by means of total questions (yes or no questions). On the basis of these answers, the Questioner attempts to make the Respondent admit a statement which contradicts the original assertion. If the Questioner succeeds, then he or she will win the dialectical game; if he or she fails, the Respondent will win.
The terms Proponent and Opponent used to refer to the core partners of an argumentative situation, are borrowed from this dialectical theory. Unlike the Proponent of a substantial proposition in an argumentative situation, the Respondent in the dialectical game does not have to build a positive proof of the proposition put forward, but must simply avoid being led into a self-contradiction.
1.3 Dialectical authority
To be worthy of a dialectical debate, the proposition must be an endoxon, that is to say, it must be endorsed by some social or intellectual authority:
Now a dialectical proposition consists in asking something that is held by all men or by most men or by philosophers, i.e., either by all, or by most, or by the most notable of these. (Top., 10)
The Aristotelian continuum values different orders of endoxa. We are far from the vision of the doxa as cliché or stereotype as “ready-to-think”, or, just as mechanically, “ready-to-denounce”.
Endoxa are opinions worthy of discussion. They define a contrario what a thesis as “a supposition of some eminent philosopher that conflicts with the general opinion”; the philosopher must be eminent, “for to take notice when any ordinary person expresses views contrary to men’s usual opinions would be silly” (Aristotle, Top., I, 11). In other words, “if it were the first comer who emitted paradoxes, it would be absurd to pay attention to it” (Aristotle, Top., Brunschwig, I, 1, 100b20, p.17). The authority entering the debate is clearly socially referenced as such.
It is remarkable to see that it is the plurality and competition between authorities — rather than the call to authority — which is placed at the core of intellectual debate. Authority is not invoked in order to close the discussion but rather to open it. To say that a proposal is supported by an authority is not to say that it is true, but to say that it deserves discussion.
2. The scholastic dispute
The scholastic dispute (disputatio) corresponds to the medieval practice of a dialectical game. It is an instrument of research and teaching, based upon a specific substantial question, as proposed by a master. At the end of the discussion, the master proposes a solution and refutes the arguments against it (Weijers 1999).
3. The revival of dialectic
The ancient dialectical method, which had been declining since the Renaissance (Ong 1958), was reconstructed in the second half of the twentieth century within the framework of logical dialogue games. It has been put at the forefront of argumentation studies by the Pragma-Dialectic and by the Informal Logic programs. The Pragma-Dialectic program of Frans van Eemeren and Rob Grootendorst (1996, etc.) is a “New Dialectic”, a counterpart of Perelman’s “New Rhetoric” (van Eemeren, Grootendorst, 1996 “La Nouvelle Dialectique” [“The New Dialectic”]). In the Informal Logic framework, the study of “logical dialogue games” has been developed by Douglas Walton (Walton 1984; Walton 1998, The New Dialectic).
In a continuation of a general definition of dialectic as, “the practice of reasoned dialogue, [the art] of arguing by questions and answers” (Brunschwig 1967, p. 10), one can consider that the conversational process is “dialectized” insofar as 1) it relates to a specific and mutually agreed problem; 2) it is played out between equal partners, 3) driven by the search for the truth, the just or the common good; 4) between which the speech circulates freely, but nonetheless 5) respects explicitly established rules.
4. Aristotelian dialectic and Hegelian dialectic
Unlike Aristotelian dialectic, Hegelian dialectic does not proceed by the elimination of the false, but by synthesis of the antagonistic positions. The original opposition is not resolved but abolished and transcended. Aristotelian dialectic is founded on the principle of non-contradiction, whereas Hegelian dialectic tends towards something “beyond” contradiction.
Nonetheless, going beyond contradiction should not imply that a speaker may hold an inconsistent discourse:
[HL] claims that “since the world is torn by contradictions, only dialectic (which admits the contradiction) makes it possible to consider it as a whole and to find out its meaning and direction”. In other words, since the world is contradiction, the idea of the world must be contradictory. The idea of a thing must be of the same nature as this thing: The idea of blue must be blue.
Julien Benda, The Betrayal of the Intellectuals, 
Conversational dialectic, made up of negotiations and adjustments, enables the opponents to save face, whereas Aristotelian dialectic does not take into account the questions of faces and politeness.
5. Rhetoric and dialectic
According to their ancient definitions, dialectic and rhetoric are the two arts of discourse. Argumentative rhetoric is “the counterpart of dialectic” (Aristotle, Rhet, I). Rhetoric is to public speech what dialectic is to private, conversational speech. Rhetoric concerns long and continuous discourse, whilst dialectic is a technique of discussion between two partners, proceeding by (brief) questions and answers. Fundamentally, dChristianityestions and answers. t, “ews contrary to men’s usual opinins would be sillly most, or by the most notable of thes, pialectic is legislative, it serves the discussion of the a priori foundations which will serve as premises for scientific deduction. Rhetoric has an executive function: it deals with current, public, legal and political affairs, and, with the development of Christianity, religious belief; it strengthens the principles that govern these practices, via epideictic means.
 Quoted after Julien Benda, La Trahison des Clercs. Excerpt from the Preface to the 1946 edition. Paris: Grasset, 1975. P. 63.