Martin (1992: 513):
This dialogic* perspective on writing is outlined in Fig. 7.7.
*Endnote #13 (p589):
Dialogic is used here in opposition to monologic referring to the extent to which the text involves turn-taking. This is not to be confused with Bakhtin's use of the term to refer to texts as heteroglossic, weaving together several discourses.
This misunderstands Bakhtin's terms 'dialogic' and 'heteroglossic'. The glossary provided in Bakhtin (1981: 428, 426) clarifies each term and the distinction between them:
The base condition governing the operation of meaning in any utterance. It is that which insures the primacy of context over text. At any given time, in any given place, there will be a set of conditions — social, historical, meteorological, physiological — that will insure that a word uttered in that place and at that time will have a meaning different than it would have under any other conditions; all utterances are heteroglot in that they are functions of a matrix of forces practically impossible to recoup, and therefore impossible to resolve. Heteroglossia is as close a conceptualisation as is possible of that locus where centripetal and centrifugal forces collide; as such, it is that which a systematic linguistics must always suppress.
Dialogism is the characteristic epistemological mode of a world dominated by heteroglossia. Everything means, is understood, as a part of a greater whole — there is a constant interaction between meanings, all of which have the potential of conditioning others. Which will affect the other, how it will do so and in what degree is what is actually settled at the moment of utterance. This dialogic imperative, mandated by the pre-existence of the language world relative to any of its current inhabitants, insures that there can be no actual monologue. One may, like a primitive tribe that knows only its own limits, be deluded into thinking there is one language, or one may, as grammarians, certain political figures and normative framers of "literary languages" do, seek in a sophisticated way to achieve a unitary language. In both cases the unitariness is relative to the overpowering force of heteroglossia, and thus dialogism.