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In Topics 1.2., Aristotle lists the uses for dialectical deduction, which is a method for reasoning from reputable opinions (ἐξ ἐνδόξων) instead of from true and primary premises (ἐξ ἀληθῶν καὶ πρώτων), as Aristotle’s scientific method the “demonstrative deduction” requires. Aristotle lists the uses for dialectical deduction as: 1. for training; 2. for ordinary encounters-i.e., casual conversation; 3. for raising difficulties in points on both sides of an argument in the philosophical sciences to find more easily which points are true or false. He then however adds, “in addition, for the first of the [principles] of each science” (ἔτι δὲ πρὸς τὰ πρῶτα τῶν περὶ ἑκάστην ἐπιστήμην [ἀρχῶν]), which is apparently an unannounced fourth use. He reasons that since these first principles are beyond argument, they can only be dealt with if one “goes through” (διέλθειν) the first principles of a science through use of endoxa. So, he says, this fourth use is particular to dialectic and that because it is investigational, it has a road to the first principles of all methods (πρὸς τᾶς ἁπασῶν τῶν μεθόδων ἀρχᾶς ὁδὸν ἔχει). (101a25-101b4).

Aristotle’s third and fourth uses are controversial as 1) Aristotle repeatedly declares that dialectic is an unsuitable method for acquiring first principles or for establishing anything as knowledge, because relies on mere opinions (APo 1.19, DA 403a2); 2) As an interrogative method dialectic is inappropriate for proving anything (SE 172a13-15, GC 316a6-11, APo 77a31-35); 3) The fact that dialectic deals with κοινά and ἀξιώματα would make it into a “universal science”.

Interpretations of uses 3 and 4 vary widely. Owen claims “the first premises of scientific argument can be established by methods which start from the endoxa”. For Irwin, some principles can be established through a “strong dialectic”. Bolton believes that use 4 is a use of peirastic dialectic as a means for examining principles, but not establishing them as principles. Smith has a different translation of the passage, which does not say that dialectic is a way to first principles at all, but rather that it merely “has a way to get through”, and Reeve believes that the role of dialectic in this case is for clarifying rather than establishing first principles.

In this paper, I argue that, in uses 3 and 4, Aristotle is describing two functions of dialectic which preliminarily aid the philosopher without proving anything whether scientifically or not. In use 3, dialectic is a means for setting out the endoxa for the argument without any use of proof, and in use 4, dialectic allows discussion of first principles of any science, but only in a preliminary way.

In one example, proponents of Aristotle endorsing premises starting from ἔνδοξα point to Nicomachean Ethics 1145b2-5:

δεῖ δ', ὥσπερ ἐπὶ τῶν ἄλλων, τιθέντας τὰ φαινόμενα καὶ πρῶτον διαπορήσαντας οὕτω δεικνύναι μάλιστα μὲν πάντα τὰ ἔνδοξα περὶ ταῦτα τὰ πάθη, εἰ δὲ μή, τὰ πλεῖστα καὶ κυριώτατα· ἐὰν γὰρ λύηταί τε τὰ δυσχερῆ καὶ καταλείπηται τὰ ἔνδοξα, δεδειγμένον ἂν εἴη ἱκανῶς.

Here, forms of δείκνυμι are used twice, which seem to show Aristotle proving from ἔνδοξα. Owen himself translates δεικνύναι as “vindicate,” in the sense that one may “justify” the φαινόμενα. I suggest “proffer with certainty,” because Aristotle is describing the process of “setting out” the φαινόμενα and going through the ἀπορίαι. The word οὕτω implies a necessary connection between what precedes it and what follows, and it would not follow (οὕτω) setting out the φαινόμενα and considering the difficulties that one proves any ἔνδοξα, but rather that the inquiry has been narrowed down. Nowhere else does the process of going through the ἀπορίαι of a problem constitute a proof, but instead it is a means for “setting up” a case. The second δείκνυμι refers to the process referred to in Topics 1.2 (διέλθειν), a case can be “rendered sufficiently.”