Aristotle, Metaphysics 4.5.14 (1010a10-15)
I’m currently reading David Sedley’s fantastic book on Plato’s Cratylus. The same Cratylus who appears in this dialogue is mentioned by Aristotle, in a passage which will serve as a warning of the dangers that can result from taking philosophy to extremes! He’s rejecting Heraclitus’ famous dictum that, like a flowing river, the world is ever-changing; this seems to have led Cratylus to decide that one cannot even use words to communicate, because they too are in a constant state of flux.
ἐκ γὰρ ταύτης τῆς ὑπολήψεως ἐξήνθησεν ἡ ἀκροτάτη δόξα τῶν εἰρημένων, ἡ τῶν φασκόντων ἡρακλειτίζειν καὶ οἵαν Κρατύλος εἶχεν, ὃς τὸ τελευταῖον οὐθὲν ᾤετο δεῖν λέγειν ἀλλὰ τὸν δάκτυλον ἐκίνει μόνον, καὶ Ἡρακλείτῳ ἐπετίμα εἰπόντι ὅτι δὶς τῷ αὐτῷ ποταμῷ οὐκ ἔστιν ἐμβῆναι· αὐτὸς γὰρ ᾤετο οὐδ’ ἅπαξ.
From this notion there blossomed the most extreme maxim of the ones I have mentioned, namely the maxim of those who call themselves followers of Heraclitus. Cratylus also held an opinion of this sort; he ended up thinking that it was not necessary to say anything, and only moved his finger. He was also critical of Heraclitus for saying that it is not possible to walk in the same river twice. For Cratylus himself thought that once could not even do it once.