Bernays indicates the probable titles of many among the lost Aristotelian Dialogues (Die Dialoge des Aristoteles, pp. 132, 133, Berlin, 1868), and gives in his book many general remarks upon them.
The observations of Aristotle in the Metaphys. (A. ἐλάττων 993, b. 1-16) are conceived in a large and just spirit. He says that among all the searchers for truth, none completely succeed, and none completely fail: those, from whose conclusions we dissent, do us service by exercising our intelligence — τὴν γὰρ ἕξιν προήσκησαν ἡμῶν. The enumeration of ἀπορίαι in the following book B of the Metaphysica is a continuation of the same views. Compare Scholia, p. 604, b. 29, Brandis.
Such compositions give something like fair play to the negative arm of philosophy; in the employment of which the Eleate Zeno first became celebrated, and the real Sokrates yet more celebrated. This negative arm is no less essential than the affirmative, to the validity of a body of reasoned truth, such as philosophy aspires to be. To know how to disprove is quite as important as to know how to prove: the one is co-ordinate and complementary to the other. And the man who disproves what is false, or guards mankind against assenting to it,[57] renders a service to philosophy, even though he may not be able to render the ulterior service of proving any truth in its place.
[57] The Stoics had full conviction of this. In Cicero’s summary of the Stoic doctrine (De Finibus, iii. 21, 72) we read:—“Ad easque virtutes, de quibus disputatum est, Dialecticam etiam adjungunt (Stoici) et Physicam: easque ambas virtutum nomine appellant: alteram (sc. Dialecticam), quod habeat rationem, ne cui falso adsentiamur, neve unquam captiosâ probabilitate fallamur; eaque, quæ de bonis et malis didicerimus, ut tenere tuerique possimus.”
Negative procedure supposed to be represented by the Sophists and the Megarici; discouraged and censured by historians of philosophy.
By historians of ancient philosophy, negative procedure is generally considered as represented by the Sophists and the Megarici, and is the main ground for those harsh epithets which are commonly applied to both of them. The negative (they think) can only be tolerated in small doses, and even then merely as ancillary to the affirmative. That is, if you have an affirmative theory to propose, you are allowed to urge such objections as you think applicable against rival theories, but only in order to make room for your own. It seems to be assumed as requiring no proof that the confession of ignorance is an intolerable condition; which every man ought to be ashamed of in himself, and which no man is justified in inflicting on any one else. If you deprive the reader of one affirmative solution, you are required to furnish him with another which you are prepared to guarantee as the true one. “Le Roi est mort — Vive le Roi”: the throne must never be vacant. It is plain that under such a restricted application, the full force of the negative case is never brought out. The pleadings are left in the hands of counsel, each of whom takes up only such fragments of the negative case as suit the interests of his client, and suppresses or slurs over all such other fragments of it as make against his client. But to every theory (especially on the topics discussed by Sokrates and Plato) there are more or less of objections applicable — even the best theory being true only on the balance. And if the purpose be to ensure a complete body of reasoned truth, all these objections ought to be faithfully exhibited, by one who stands forward as their express advocate, without being previously retained for any separate or inconsistent purpose.
Vocation of Sokrates and Plato for the negative procedure: absolute necessity of it as a condition of reasoned truth. Parmenidês of Plato.
How much Plato himself, in his dialogues of search, felt his own vocation as champion of the negative procedure, we see marked conspicuously in the dialogue called Parmenidês. This dialogue is throughout a protest against forward affirmation, and an assertion of independent locus standi for the negationist and objector. The claims of the latter must first be satisfied, before the affirmant can be considered as solvent. The advocacy of those claims is here confided to veteran Parmenides, who sums them up in a formidable total: Sokrates being opposed to him under the unusual disguise of a youthful and forward affirmant. Parmenides makes no pretence of advancing any rival doctrine. The theories which he selects for criticism are the Platonic theory of intelligible Concepts, and his own theory of the Unum: he indicates how many objections must be removed — how many contradictions must be solved — how many opposite hypotheses must be followed out to their results — before either of these theories can be affirmed with assurance. The exigencies enumerated may and do appear insurmountable:[58] but of that Plato takes no account. Such laborious exercises are inseparable from the process of searching for truth, and unless a man has strength to go through them, no truth, or at least no reasoned truth, can be found and maintained.[59]
[58] Plato, Parmenid. p. 136 B. δεῖ σκοπεῖν — εἰ μέλλεις τελέως γυμνασάμενος κυρίως διόψεσθαι τὸ ἀληθές. Ἀμήχανον, ἔφη, λέγεις, ὦ Παρμενίδη, πραγματείαν, &c.
Aristotle declares that no man can be properly master of any affirmative truth without having examined and solved all the objections and difficulties — the negative portion of the enquiry. To go through all these ἀπορίας is the indispensable first stage, and perhaps the enquirer may not be able to advance farther, see Metaphysic. B. 995, a. 26, 996, a. 16 — one of the most striking passages in his works. Compare also what he says, De Cœlo, ii. 294, b. 10, διὸ δεῖ τὸν μέλλοντα καλῶς ζητήσειν ἐνστατικὸν εἶναι διὰ τῶν οἰκείων ἐνστάσεων τῷ γένει, τοῦτο δὲ ἐστὶν ἐκ τοῦ πάσας τεθεωρηκέναι τὰς διαφοράς.