[34] Ibid. p. 1009, a. 8-20. ἀνάγκη πάντα ἅμα ἀληθῆ καὶ ψευδῆ εἶναι. — p. 1011, a. 30.
I have already in another work,[35] while analysing the Platonic dialogues Theætêtus and Kratylus, criticized at some length the doctrine here laid down by Plato and Aristotle. I have endeavoured to show that the capital tenet of Protagoras is essentially distinct from the other tenets with which these two philosophers would identify it: distinct both from the dogma of Herakleitus, That everything is in unceasing flux and process, each particular moment thereof being an implication of contradictions both alike true; and distinct also from the other dogma held by others, That all cognition is sensible perception. The Protagorean tenet “Homo Mensura� is something essentially distinct from either of these two; though possibly Protagoras himself may have held the second of the two, besides his own. His tenet is nothing more than a clear and general declaration of the principle of universal Relativity. True belief and affirmation have no meaning except in relation to some believer, real or supposed; true disbelief and negation have no meaning except in relation to some disbeliever, real or supposed. When a man affirms any proposition as true, he affirms only what he (perhaps with some other persons also) believes to be true, while others may perhaps disbelieve it as falsehood. Object and Subject are inseparably implicated: we may separate them by abstraction, and reason about each apart from the other; but, as reality, they exist only locked up one with the other.
[35] ‘Plato and the Other Companions of Sokrates,’ Vol. II. [c. xxvi.] pp. 325-363: “The Protagorean doctrine — Man is the measure of all things — is simply the presentation in complete view of a common fact; uncovering an aspect of it which the received phraseology hides. Truth and Falsehood have reference to some believing subject — and the words have no meaning except in that relation. Protagoras brings to view this subjective side of the same complex fact, of which Truth and Falsehood denote the objective side. He refuses to admit the object absolute — the pretended thing in itself — Truth without a believer. His doctrine maintains the indefeasible and necessary involution of the percipient mind in every perception — of the concipient mind in every conception — of the cognizant mind in every cognition. Farther, Protagoras acknowledges many distinct believing or knowing Subjects: and affirms that every object known must be relative to (or in his language, measured by) the knowing Subject: that every cognitum must have its cognoscens, and every cognoscibile its cognitionis capax; that the words have no meaning unless this be supposed; that these two names designate two opposite poles or aspects of the indivisible fact of cognition — actual or potential — not two factors, which are in themselves separate or separable, and which come together to make a compound product. A man cannot in any case get clear of or discard his own mind as a Subject. Self is necessarily omnipresent, concerned in every moment of consciousness, &c.� Compare also [c. xxiv. p. 261.]
That such is and always has been the state of the fact, in regard to truth and falsehood, belief and disbelief, is matter of notoriety: Protagoras not only accepts it as a fact, but formulates it as a theory. Instead of declaring that what he (or the oracle which he consults and follows) believes to be true, is absolute truth, while that which others believe, is truth relatively to them, — he lowers his own pretensions to a level with theirs. He professes to be a measure of truth only for himself, and for such as may be satisfied with the reasons that satisfy him. Aristotle complains that this theory discourages the search for truth as hopeless, not less than the chase after flying birds.[36] But, however serious such discouragement may be, we do not escape the real difficulty of the search by setting up an abstract idol and calling it Absolute Truth, without either relativity or referee; while, if we enter, as sincere and bonâ fide enquirers, on the search for reasoned truth or philosophy, we shall find ourselves not departing from the Protagorean canon, but involuntarily conforming to it. Aristotle, after having declared that the Maxim of Contradiction was true beyond the possibility of deception,[37] but yet that there were several eminent philosophers who disallowed it, is forced to produce the best reasons in his power to remove their doubts and bring them round to his opinion. His reasons must be such as to satisfy not his own mind only, but the minds of opponents and indifferent auditors as referees. This is an appeal to other men, as judges each for himself and in his own case: it is a tacit recognition of the autonomy of each individual enquirer as a measure of truth to himself. In other words, it is a recognition of the Protagorean canon.
[36] Aristot. Metaph. Γ. v. p. 1009, b. 38.
[37] Ibid. Γ. iii. p. 1005, b. 11: βεβαιοτάτη δ’ ἀρχὴ πασῶν, περὶ ἣν διαψευσθῆναι ἀδύνατον.
We know little about the opinions of Protagoras; but there was nothing in this canon necessarily at variance either with the Maxim of Contradiction or with that of Excluded Middle. Both Aristotle and Plato would have us believe that Protagoras was bound by his canon to declare every opinion to be alike false and true, because every opinion was believed by some and disbelieved by others.[38] But herein they misstate his theory. He did not declare any thing to be absolutely true, or to be absolutely false. Truth and Falsehood were considered by him as always relative to some referee, and he recognized no universal or infallible referee. In his theory the necessity of some referee was distinctly enunciated, instead of being put out of sight under an ellipsis, as in the received theories and practice. And this is exactly what Plato and Aristotle omit, when they refute him. He proclaimed that each man was a measure for himself alone, and that every opinion was true to the believer, false to the disbeliever; while they criticize him as if he had said — Every opinion is alike true and false; thus leaving out the very qualification which forms the characteristic feature of his theory. They commit that fallacy which Plato shows up in the Euthydêmus, and which Aristotle[39] numbers in his list of Fallaciæ Extra Dictionem, imputing it as a vice to the Sophists: they slide à dicto secundum quid ad dictum simpliciter. And it is remarkable that Aristotle, in one portion of his argument against “Homo Mensura,� expressly admonishes the Protagoreans that they must take care to adhere constantly to this qualified mode of enunciation;[40] that they must not talk of apparent truth generally, but of truth as it appears to themselves or to some other persons, now or at a different time. Protagoras hardly needed such an admonition to keep to what is the key-note and characteristic peculiarity of his own theory; since it is only by suppressing this peculiarity that his opponents make the theory seem absurd. He would by no means have disclaimed that consequence of his theory, which Aristotle urges against it as an irrefragable objection; viz., that it makes every thing relative, and recognizes nothing as absolute. This is perfectly true, and constitutes its merit in the eyes of its supporters.
[38] Plato, Theætêt. pp. 171-179. Aristot. Met. Γ. iv. p. 1007, b. 21: εἰ κατὰ παντός τι ἢ καταφῆσαι ἢ ἀποφῆσαι ἐνδέχεται, καθάπερ ἀνάγκη τοῖς τὸν Πρωταγόρου λέγουσι λόγον. Compare v. p. 1009, a. 6; viii. p. 1012, b. 15.
[39] Aristot. Soph. El. p. 167, a. 3; Rhetoric. II. xxiv. p. 1402, a. 2-15. ὥσπερ καὶ ἐπὶ τῶν ἐριστικῶν τὸ κατά τι καὶ πρός τι καὶ πῇ οὐ προστιθέμενα ποιεῖ τὴν συκοφαντίαν.
[40] Aristot. Metaph. Γ. vi. p. 1011, a. 21: διὸ καὶ φυλακτέον τοῖς τὴν βίαν ἐν τῷ λόγῳ ζητοῦσιν, ἅμα δὲ καὶ ὑπέχειν λόγον ἀξιοῦσιν, ὅτι οὐ τὸ φαινόμενον ἔστιν, ἀλλὰ τὸ φαινόμενον ᾧ φαίνεται καὶ ὅτε φαίνεται καὶ ᾗ καὶ ὥς. — b. 1: ἀλλ’ ἴσως διὰ τοῦτ’ ἀνάγκη λέγειν τοῖς μὴ δι’ ἀπορίαν ἀλλὰ λόγου χάριν λέγουσιν, ὅτι οὐκ ἔστιν ἀληθὲς τοῦτο, ἀλλὰ τούτῳ ἀληθές.