A dialogue does not have seating limits.
The following is pure myth, and Greek myth at that: “Only two people can engage in dialogue.”
Any number of people can engage in dialogue, for two reasons. One is that other than monologue, we have no accepted words specifying the number of people in conversation—for instance, we have but rare use of trialogue, no quatralogue, no sesquilogue, no kilologue (even in these social networking days).
The other, more important, reason is that the di- in dialogue has nothing to do with the number two, not even back through the word’s Latin and Greek origins. Dialogue traces back to Greek dialegsthai, “to converse.” Dialegsthai is also the ultimate source of another of our language words: dialect. So, let’s for a moment
employ the persnickitorial logic of the law of Xtreme Etymological Stasis (the “two people can play that game” rule): if only two people can engage in dialogue, then there can be only two dialects.
And that is the end of this monologic diatribe.