Aristotle often contrasts dialectical arguments with demonstrations.
The difference, he tells us, is in the character of their premises, not in their logical structure:
– whether an argument is a sullogismos is only a matter of whether its conclusion results of necessity from its premises.
The premises of demonstrations must be true and primary, that is, not only true but also prior to their conclusions in the way explained in the Posterior Analytics.
The premises of dialectical deductions, by contrast, must be accepted (endoxos).
Dialectical Premises: The Meaning of Endoxos
Recent scholars have proposed different interpretations of the term endoxos.
Aristotle often uses this adjective as a substantive: ta endoxa, “accepted things”, “accepted opinions”.
On one understanding, descended from the work of G. E. L. Owen and developed more fully by Jonathan Barnes and especially Terence Irwin, the endoxa are a compilation of views held by various people with some form or other of standing:
– “the views of fairly reflective people after some reflection”, in Irwin’s phrase.
Dialectic is then simply “a method of argument from [the] common beliefs [held by these people]”.
For Irwin, then, endoxa are “common beliefs”.
Jonathan Barnes, noting that endoxa are opinions with a certain standing, translates with “reputable”.
My own view is that Aristotle’s texts support a somewhat different understanding.
He also tells us that dialectical premises differ from demonstrative ones in that the former are questions, whereas the latter are assumptions or assertions:
– “the demonstrator does not ask, but takes”, he says.
This fits most naturally with a view of dialectic as argument directed at another person by question and answer and consequently taking as premises that other person’s concessions.
Anyone arguing in this manner will, in order to be successful, have to ask for premises which the interlocutor is liable to accept, and the best way to be successful at that is to have an inventory of acceptable premises, i.e., premises that are in fact acceptable to people of different types.
In fact, we can discern in the Topics (and the Rhetoric, which Aristotle says depends on the art explained in the Topics) an art of dialectic for use in such arguments.
My reconstruction of this art (which would not be accepted by all scholars) is as follows.