[27] Aristot. Met. Γ. iv. p. 1008, a. 18-b. 12: εἰ δὲ ὁμοίως καὶ ὅσα ἀποφῆσαι φάναι ἀνάγκη — πάντα δ’ ἂν εἴη ἕν — οὐθὲν διοίσει ἕτερον ἑτέρου — εἰ δὲ μηθὲν ὑπολαμβάνει ἀλλ’ ὁμοίως οἴεται καὶ οὐκ οἴεται, τί ἂν διαφερόντως ἔχοι τῶν φυτῶν; K. v. p. 1062, a. 28.
The man who professes this doctrine, however (continues Aristotle[28]), shows plainly by his conduct that his mind is not thus blank; that, in respect of the contradictory alternative, he does not believe either both sides or neither side, but believes one and disbelieves the other. When he feels hungry, and seeks what he knows to be palatable and wholesome, he avoids what he knows to be nasty and poisonous. He knows what is to be found in the market-place, and goes there to get it; he keeps clear of falling into a well or walking into the sea; he does not mistake a horse for a man. He may often find himself mistaken; but he shows by his conduct that he believes certain subjects to possess certain definite attributes, and not to possess others. Though we do not reach infallible truth, we obtain an approach to it, sometimes nearer, sometimes more remote; and we thus escape the extreme doctrine which forbids all definite affirmation.[29]
[28] Ibid. Γ. iv. p. 1008, b. 12-31; K. vi. p. 1063, a. 30.
[29] Ibid. Γ. iv. p. 1008, b. 36: εἰ οὖν τὸ μᾶλλον ἐγγύτερον, εἴη γε ἄν τι ἀληθὲς οὗ ἐγγύτερον τὸ μᾶλλον ἀληθές· κἂν εἰ μή ἐστιν, ἀλλ’ ἤδη γέ τι ἐστὶ βεβαιότερον καὶ ἀληθινώτερον, καὶ τοῦ λόγου ἀπηλλαγμένοι ἂν εἴημεν τοῦ ἀκράτου καὶ κωλύοντός τι τῇ διανοίᾳ ὁρίσαι.
It is in this manner that Aristotle, vindicating the Maxims of Contradiction and of Excluded Middle as the highest principia of syllogistic reasoning, disposes of the two contemporaneous dogmas that were most directly incompatible with these Maxims:— (1) The dogma of Herakleitus, who denied all duration or permanence of subject, recognizing nothing but perpetual process, flux, or change, each successive moment of which involved destruction and generation implicated with each other: Is and is not are both alike and conjointly true, while neither is true separately, to the exclusion of the other;[30] (2) The dogma of Anaxagoras, who did not deny fixity or permanence of subject, but held that everything was mixed up with everything; that every subject had an infinite assemblage of contrary predicates, so that neither of them could be separately affirmed or separately denied: The truth lies in a third alternative or middle, between affirmation and denial.[31]
[30] Aristot. Met. A. vi. p. 987, a. 34; Γ. v. p. 1010, a. 12: Κράτυλος — ὃς τὸ τελευταῖον οὐθὲν ᾤετο δεῖν λέγειν ἀλλὰ τὸν δάκτυλον ἐκίνει μόνον, καὶ Ἡρακλείτῳ ἐπετίμα εἰπόντι ὅτι δὶς τῷ αὐτῷ ποτάμῳ οὐκ ἔστιν ἐμβῆναι· αὐτὸς γὰρ ᾤετο οὔδ’ ἁπάξ. Herakleitus adopted as his one fundamentum Fire or Heat, as being the principle of mobility or change: χρῶνται γὰρ ὡς κινητικὴν ἔχοντι τῷ πυρὶ τὴν φύσιν — Metaph. A. iii. p. 984, b. 5. Ibid. K. v. p. 1062, a. 31-b. 10; K. x. p. 1067, a. 5; M. iv. p. 1078, b. 15.
[31] Aristot. Met. K. vi. p. 1063, b. 25; A. viii. p. 989, a. 31-b. 16. ὅτε γὰρ οὐθὲν ἦν ἀποκεκριμένον, δῆλον ὡς οὐθὲν ἦν ἀληθὲς εἰπεῖν κατὰ τῆς οὐσίας ἐκείνης, λέγω δ’ οἷον ὅτι οὔτε λευκὸν οὔτε μέλαν ἢ φαιὸν ἢ ἄλλο χρῶμα, ἀλλ’ ἄχρων ἦν ἐξ ἀνάγκης· ὁμοίως δὲ καὶ ἄχυμον τῷ αὐτῷ λόγῳ τούτῳ, οὐδὲ ἄλλο τῶν ὁμοίων οὐθέν· οὔτε γὰρ ποιόν τι οἷόν τε αὐτὸ εἶναι οὔτε ποσὸν οὔτε τί. — Γ. iv. b. 1007, b. 25: καὶ γίγνεται δὴ τὸ τοῦ Ἀναξαγόρου, ὁμοῦ πάντα χρήματα· ὥστε μηθὲν ἀληθῶς ὑπάρχειν. — Γ. viii. p. 1012, a. 24: ἔοικε δ’ ὁ μὲν Ἡρακλείτου λόγος, λέγων πάντα εἶναι καὶ μὴ εἶναι, ἅπαντα ἀληθῆ ποιεῖν, ὁ δ’ Ἀναξαγόρου εἶναί τι μεταξὺ τῆς ἀντιφάσεως, ὥστε πάντα ψευδῆ· ὅταν γὰρ μιχθῇ, οὔτ’ ἀγαθὸν οὔτ’ οὐκ ἀγαθὸν τὸ μῖγμα, ὥστ’ οὐθὲν εἰπεῖν ἀληθές.
Having thus refuted these dogmas to his own satisfaction, Aristotle proceeds to impugn a third doctrine which he declares to be analogous to these two and to be equally in conflict with the two syllogistic principia which he is undertaking to vindicate. This third doctrine is the “Homo Mensura� of Protagoras: Man is the measure of all things — the measure of things existent as well as of things non-existent: To each individual that is true or false which he believes to be such, and for as long as he believes it. Aristotle contends that this doctrine is homogeneous with those of Herakleitus and Anaxagoras, and must stand or fall along with them; all three being alike adverse to the Maxim of Contradiction.[32] Herein he follows partially the example of Plato, who (in his Theætêtus[33]), though not formally enunciating the Maxim of Contradiction, had declared the tenets of Protagoras to be coincident with or analogous to those of Herakleitus, and had impugned both one and the other by the same line of arguments. Protagoras agreed with Herakleitus (so Plato and Aristotle tell us) in declaring both affirmative and negative (in the contradictory alternative) to be at once and alike true; for he maintained that what any person believed was true, and that what any person disbelieved was false. Accordingly, since opinions altogether opposite and contradictory are held by different persons or by the same person at different times, both the affirmative and the negative of every Antiphasis must be held as true alike;[34] in other words, all affirmations and all negations were at once true and false. Such co-existence or implication of contradictions is the main doctrine of Herakleitus.
[32] Aristot. Met Γ. v. p. 1009, a. 6: ἔστι δ’ ἀπὸ τῆς αὐτῆς δόξης καὶ ὁ Πρωταγόρου λόγος, καὶ ἀνάγκη ὁμοίως ἄμφω αὐτοὺς ἢ εἶναι ἢ μὴ εἶναι.
[33] Aristotle refers here to Plato by name, Metaphys. Γ. v. p. 1010, b. 12.