- διδασκαλικὸς λόγος (didactic speech): The person asking questions (a teacher) knows the truth, while the person responding (the student) does not (and presumably knows that he does not, or else peirastic speech should be used first). The conversation proceeds on the basis of principles of the domain of knowledge under discussion: a discussion about programming languages would involve prior special knowledge of those languages and not necessarily be accessible to the layperson. The goal of the conversation is to teach a student special knowledge.
- πειραστικὸς λόγος (examination speech): The person asking questions tries to test the person answering, because the person answering claims to know the truth. This could be a simple examination, like a test in school, or it could be "Socratic questioning" as Socrates usually practiced it in Plato's dialogues: Socrates happens upon someone who claims to understand something very well, so Socrates asks him questions about his beliefs until he exposes inconsistency. This kind of speech can either confirm that the respondent knows what he's talking about or does not, and, if it reveals that he held false beliefs, showing him his error makes him readier to learn more correct beliefs through didactic speech.
- διαλεκτικὸς λόγος (ordinary conversation): Two people, neither of whom fully knows the truth of what they're saying, begin from common sense and commonly held opinions, aiming to refine their understanding of ordinary matters in general and probable terms.
- ἐριστικὸς λόγος (competitive conversation): Someone gets roped into responding to questions; the questioner's goal, however, is simply to appear (visibly, in front of other people) to win the argument, whether or not he actually does win. The questioner does not necessarily possess the truth or any better beliefs than the respondent, but he does have strategies of false argumentation (the fallacies Aristotle outlines in his _Sophistici Elenchi_) that will fool everyone else and give him an apparent victory.
Serious discussions should be one of the first two types; internet discussions are almost invariably the last.