Cratylus (440)

Socrates. No, nor can it be known by anyone. For at the moment when he who seeks to know it approaches, it becomes something else and different, so that its nature and state can no longer be known; and surely there is no knowledge which knows that which is in no state.

Cratylus. It is as you say.

Socrates. But we cannot even say that there is any knowledge, if all things are changing and nothing remains fixed; for if knowledge itself does not change and cease to be knowledge, then knowledge would remain, and there would be knowledge; but if the very essence of knowledge changes, at the moment of the change to another essence of knowledge there would be no knowledge, and if it is always changing, there will always be no knowledge, and by this reasoning there will be neither anyone to know nor anything to be known. But if there is always that which knows and that which is known—if the beautiful, the good, and all the other verities exist—I do not see how there is any likeness between these conditions of which I am now speaking and flux or motion. Now whether this is the nature of things, or the doctrine of Heracleitus and many others is true, is another question; but surely no man of sense can put himself and his soul under the control of names, and trust in names and their makers to the point of affirming that he knows anything; nor will he condemn himself and all things and say that there is no health in them, but that all things are flowing like leaky pots, or believe that all things are just like people afflicted with catarrh, flowing and running all the time. Perhaps, Cratylus, this theory is true, but perhaps it is not. Therefore you must consider courageously and thoroughly and not accept anything carelessly—for you are still young and in your prime; then, if after investigation you find the truth, impart it to me.

Cratylus. I will do so. However, I assure you, Socrates, that I have already considered the matter, and after toilsome consideration I think the doctrine of Heracleitus is much more likely to be true.

Socrates. Some other time, then, my friend, you will teach me, when you come back; but now go into the country as you have made ready to do; and Hermogenes here will go with you a bit.

Cratylus. Very well, Socrates, and I hope you also will continue to think of these matters.