The reply to the second part of MM MacKenzie's argument is easiest.
Now it is true that Heraclitus could have proposed a thesis of indeterminacy without recognizing its consequences for the proposal itself, and without realizing that this commits him to self-refutation as soon as he opens his mouth; so that this is only indirect evidence against this interpretation of the paradoxical arguments.But isn't this, rather, indirect evidence for the interpretation? No mistake is more common among philosophers than to propose a theory that cannot account for their own philosophizing. They do this repeatedly, even when they echo theories which have already been refuted in that way. When Hume said: "Pay no attention to statements belonging neither to mathematics nor to experimental science", he committed himself to self-refutation as soon as he opened his mouth, yet that didn't stop the Wiener Kreis from doing exactly the same thing 150 years later.
Plato refutes Protagoras in that way; he refutes Parmenides likewise. In fact, it's something of a special technique of Plato--isn't it?--to bring the theorist into his own picture and point out that the resulting complex is incoherent. (Hence the especial sting when in the dialogue Parmenides points out that the theory of Forms is exposed to exactly the same sort of objection!) That Plato thinks this way about the 'flux' interpretation of Heraclitus, I think, makes it more likely that that interpretation is correct.
Okay, let's turn to the first paragraph:
In the first place, the surviving evidence does not support it.But doesn't that claim beg the question? If one accepts that Plato's report of the river utterance is genuine, one needs to explain why, by parity, one doesn't accept a saying along the lines of "Everything gives way; nothing remains"(see post below).
His cosmology has internal problems, as we shall see; none the less, it does not present us with a flux-ridden view of the world, but rather one in which the elements change in a regular cycle (cf. e.g. 31).Perhaps that is Heraclitus' view, but even so, change in a regular cycle is still change! (I believe it's one of Guthrie's key arguments that a system oscillating between two extremes is nonetheless constantly changing.) --"But the cycle is regular." --Is it? Exactly regular? Why should we say that?
It is of course begging the question to say that the river paradox is an analogy for the flux of the world...I'm not sure that relying on the interpretation that Plato supplies when he introduces Heraclitus' river image is precisely begging the question; also, it's certain that Heraclitus is not talking only about rivers. But, again, the question-- to be begged or not--is not whether the river fragment itself demonstrates that Heraclitus held to 'universal flux', but rather why we shouldn't ascribe this view to him.
... and even if it were, the river is conceded to remain stable and determinate ('the same river') even while the waters change.But this consideration needn't move the flux advocate, as James Warren aptly points out.
Z Z Z Z Z z z z z z z z z z z z z z z z z z z z..... (I've lapsed back into my Guthrian slumbers).