[74] Plato, Phædrus, p. 271 D-E; compare 258 A.
Contrast with the Treatise De Legibus — Plato assumes infallible authority — sets aside Dialectic.
Though Sokrates, and Plato so far forth as follower of Sokrates, employed a colloquial method based on the fundamental assumption of the Protagorean formula — autonomy of each individual mind — whether they accepted the formula in terms, or not; yet we shall find Plato at the end of his career, in his treatise De Legibus, constructing an imaginary city upon the attempted deliberate exclusion of this formula. We shall find him there monopolising all teaching and culture of his citizens from infancy upwards, barring out all freedom of speech or writing by a strict censorship, and severely punishing dissent from the prescribed orthodoxy. But then we shall also find that Plato in that last stage of his life — when he constitutes himself as lawgiver, the measure of truth or falsehood for all his citizens — has at the same time discontinued his early commerce with the Sokratic Dialectics.
Plato in denying the Protagorean formula, constitutes himself the measure for all. Counter-proposition to the formula.
On the whole then, looking at what Plato says about the Protagorean doctrine of Relativity — Homo Mensura — first, his statement what the doctrine really is, next his strictures upon it — we may see that he ascribes to it consequences which it will not fairly carry. He impugns it as if it excluded philosophy and argumentative scrutiny: whereas, on the contrary, it is the only basis upon which philosophy or “reasoned truth” can stand. Whoever denies the Protagorean autonomy of the individual judgment, must propound as his counter theory some heteronomy, such as he (the denier) approves. If I am not allowed to judge of truth and falsehood for myself, who is to judge for me? Plato, in the Treatise De Legibus, answers very unequivocally:— assuming to himself that infallibility which I have already characterised as the prerogative of King Nomos: “I, the lawgiver, am the judge for all my citizens: you must take my word for what is true or false: you shall hear nothing except what my censors approve — and if, nevertheless, any dissenters arise, there are stringent penalties in store for them”. Here is an explicit enunciation of the Counter-Proposition,[75] necessary to be maintained by those who deny the Protagorean doctrine. If you pronounce a man unfit to be the measure of truth for himself, you constitute yourself the measure, in his place: either directly as lawgiver — or by nominating censors according to your own judgment. As soon as he is declared a lunatic, some other person must be appointed to manage his property for him. You can only exchange one individual judgment for another. You cannot get out of the region of individual judgments, more or fewer in number: the King, the Pope, the Priest, the Judges or Censors, the author of some book, or the promulgator of such and such doctrine. The infallible measure which you undertake to provide, must be found in some person or persons — if it can be found at all: in some person selected by yourself — that is, in the last result, yourself.[76]
[75] Professor Ferrier’s Institutes of Metaphysic exhibit an excellent example of the advantages of setting forth explicitly the Counter-Proposition — that which an author intends to deny, as well as the Proposition which he intends to affirm and prove.
[76] Aristotle says (Ethic. Nikomach. x. 1176, a. 15) δοκεῖ δ’ ἐν ἅπασι τοῖς τοιούτοις εἶναι τὸ φαινόμενον τῷ σπουδαίῳ. “That is, which appears to be in the judgment of the wise or virtuous man.” The ultimate appeal is thus acknowledged to be, not to an abstraction, but to some one or more individual persons whom Aristotle recognises as wise. That is truth which this wise man declares to be truth. You cannot escape from the Relative by any twist of reasoning.
What Platonic critics call “Der Gegensatz des Seins und des Scheins“ (see Steinhart, Einleit. zum Theætêt. p. 37) is unattainable. All that is attainable is the antithesis between that which appears to one person, and that which appears to one or more others, choose them as you will: between that which appears at a first glance, or at a distance, or on careless inspection — and that which appears after close and multiplied observations and comparisons, after full discussion, &c. Das Sein is that which appears to the person or persons whom we judge to be wise, under these latter favourable circumstances.
Epiktetus, i. 28, 1. Τί ἔστιν αἴτιον τοῦ συγκατατίθεσθαί τινι; Τὸ φαίνεσθαι ὅτι ὑπάρχει. Τῷ οὖν φαινομένῳ ὅτι οὐχ ὑπάρχει, συγκατατίθεσθαι οὐχ οἷόν τε.
Import of the Protagorean formula is best seen when we state explicitly the counter-proposition.