Cratylus (426)

Socrates. All these are merely very clever evasions on the part of those who refuse to offer any rational theory of the correctness of the earliest names. And yet if anyone is, no matter why, ignorant of the correctness of the earliest names, he cannot know about that of the later, since they can be explained only by means of the earliest, about which he is ignorant. No, it is clear that anyone who claims to have scientific knowledge of names must be able first of all to explain the earliest names perfectly, or he can be sure that what he says about the later will be nonsense. Or do you disagree?

Hermogenes. No, Socrates, not in the least.

Socrates. Now I think my notions about the earliest names are quite outrageous and ridiculous. I will impart them to you, if you like; if you can find anything better, please try to impart it to me.

Hermogenes. I will do so. Go on, and do not be afraid.

Socrates. First, then, the letter rho seems to me to be an instrument expressing all motion. We have not as yet said why motion has the name κίνησις; but it evidently should be ἴεσις, for in old times we did not employ eta, but epsilon. And the beginning of κίνησις is from κίειν, a foreign word equivalent to ἰέναι (go). So we should find that the ancient word corresponding to our modern form would be ἴεσις; but now by the employment of the foreign word κίειν, change of epsilon to eta, and the insertion of nu it has become κίνησις, though it ought to be κιείνεσις or εἶσις. And στάσις (rest) signifies the negation of motion, but is called στάσις for euphony. Well, the letter rho, as I was saying, appeared to be a fine instrument expressive of motion to the name-giver who wished to imitate rapidity, and he often applies it to motion. In the first place, in the words ῥεῖν (flow) and ῥοή (current) he imitates their rapidity by this letter, then in τρόμος (trembling) and in τρέχειν (run), and also in such words as κρούειν (strike), θραύειν (break), ἐρείκειν (rend), θρύπτειν (crush),κερματίζειν (crumble), ῥυμβεῖν (whirl), he expresses the action of them all chiefly by means of the letter rho; for he observed, I suppose, that the tongue is least at rest and most agitated in pronouncing this letter, and that is probably the reason why he employed it for these words. Iota again, he employs for everything subtle, which can most readily pass through all things.