[13] Plato, Repub. i. p. 337 C. Εἰ δ’ οὖν καὶ μὴ ἔστιν ὅμοιον, φαίνεται δὲ τῷ ἐρωτηθέντι τοιοῦτον, ἧττόν τι αὐτὸν οἴει ἀποκρινεῖσθαι τὸ φαινόμενον ἑαυτῷ, ἐάν τε ἡμεῖς ἀπαγορεύωμεν, ἐάν τε μή; Ἄλλο τι οὖν, ἔφη, καὶ σὺ οὕτω ποιήσεις; ὧν ἐγὼ ἀπεῖπον, τούτων τι ἀποκρινεῖ; Οὐκ ἂν θαυμάσαιμι, ἦν δ’ ἐγώ, εἴ μοι σκεψαμένῳ οὕτω δόξειεν.
This passage deserves notice, inasmuch as Plato here affirms, in very plain language, the Protagorean doctrine, which we have seen him trying to refute in the Theætêtus and Kratylus, — “Homo Mensura, — Every man is a measure to himself. That is true or false to every man which appears to him so.”
Most of Plato’s dialogues indeed imply this truth; for no man makes more constant appeal to the internal assent or dissent of the individual interlocutor. But it is seldom that he declares it in such express terms.
[14] Plato, Republic, i. p. 337 D.
Definition given by Thrasymachus — Justice is that which is advantageous to the more powerful. Comments by Sokrates. What if the powerful man mistakes his own advantage?
After a few more words, in the same offensive and insolent tone ascribed to him from the beginning, Thrasymachus produces his definition of Justice:— “Justice is that which is advantageous to the more powerful”. Some comments from Sokrates bring out a fuller explanation, whereby the definition stands amended:— “Justice is that which is advantageous to the constituted authority, or to that which holds power, in each different community: monarchy, oligarchy, or democracy, as the case may be. Each of these authorities makes laws and ordinances for its own interest: declares what is just and unjust: and punishes all citizens who infringe its commands. Justice consists in obeying these commands. In this sense, justice is everywhere that which is for the interest or advantage of the more powerful.”[15] “I too believe” (says Sokrates) “that justice is something advantageous, in a certain sense. But whether you are right in adding these words — ‘to the more powerful’ — is a point for investigation.[16] Assuming that the authorities in each state make ordinances for their own advantage, you will admit that they sometimes mistake, and enact ordinances tending to their own disadvantage. In so far as they do this, justice is not that which is advantageous, but that which is disadvantageous, to the more powerful.[17] Your definition therefore will not hold.”
[15] Plato, Republic, i. pp. 338-339.
[16] Plato, Republic, i. p. 339 B. ἐπειδὴ γὰρ ξυμφέρον γέ τι εἶναι καὶ ἐγὼ ὁμολογῶ τὸ δίκαιον, σὺ δὲ προστίθης καὶ αὐτὸ φὴς εἶναι τὸ τοῦ κρείττονος, ἐγὼ δὲ ἀγνοῶ, σκεπτέον δή.
[17] Plato, Republic, i. p. 339 E.
Correction by Thrasymachus — if the Ruler mistakes, he is pro tanto no Ruler — The Ruler, quâ Ruler — quâ Craftsman — is infallible.