[74] Plato, Krat. pp. 438-439. 438 E:— δι’ ἀλλήλων γε, εἴ πῃ ξυγγενῆ ἐστί, καὶ αὐτὰ δι’ αὑτῶν.
Unchangeable Platonic Forms — opposed to the Herakleitean flux, which is true only respecting sensible particulars.
Sokrates then concludes the dialogue by opposing the Platonic ideas to the Herakleitean theory. I often dream or imagine the Beautiful per se, the Good per se, and such like existences or Entia.[75] Are not such existences real? Are they not eternal, unchangeable and stationary? Particular beautiful things — particular good things — are in perpetual change or flux: but The Beautiful, The Good — The Ideas or Forms of these and such like — remain always what they are, always the same.
[75] Plato, Krat. p. 439 C-D. σκέψαι ὁ ἔγωγε πολλάκις ὀνειρώττω, πότερον φῶμέν τι εἶναι αὐτὸ καλὸν καὶ ἀγαθὸν καὶ ἓν ἕκαστον τῶν ὄντων οὕτως, ἢ μή; …
μὴ εἰ πρόσωπόν τί ἐστι καλὸν ἤ τι τῶν τοιοῦτων, καὶ δοκεῖ ταῦτα πάντα ῥεῖν· ἀλλ’ αὐτὸ τὸ καλὸν οὐ τοιοῦτον ἀεί ἐστιν οἷόν ἐστιν;
The Herakleitean theory of constant and universal flux is true respecting particular things, but not true respecting these Ideas or Forms. It is the latter alone which know or are known: it is they alone which admit of being rightly named. For that which is in perpetual flux and change can neither know, nor be known, nor be rightly named.[76] Being an ever-changing subject, it is never in any determinate condition: and nothing can be known which is not in a determinate condition. The Form of the knowing subject, as well as the Form of the known object, must both remain fixed and eternal, otherwise there can be no knowledge at all.
[76] Plato, Kratyl. p. 439 D — 440 A. Ἆρ’ οὖν οἷόν τε προσειπεῖν αὐτὸ ὀρθως, εἰ ἀεὶ ὑπεξέρχεται, πρῶτον μὲν ὅτι, ἐκεινό ἐστιν, ἔπειτα ὅτι τοιοῦτων; ἢ ἀνάγκη ἄμα ἡμῶν λεγόντων ἄλλο αὐτὸ εὐθὺς γίγνεσθαι καὶ ὑπεξιέναι, καὶ μηκέτι οὕτως ἔχειν; …
Ἀλλὰ μὴν οὐδ’ ἂν γνωσθείη γε ὑπ’ οὐδενός.…
Ἀλλ’ οὐδὲ γνωσιν εἶναι φάναι εἰκός, εἰ μεταπίπτει πάντα χρήματα καὶ μηδὲν μένει.
Herakleitean theory must not be assumed as certain. We must not put implicit faith in names.