Cratylus c. 460 BC – c. 380 BC

Cratylus was a Greek philosopher of late fifth and early fourth century BC Athens, an Heraclitean who carried the doctrine of universal flux to its extreme conclusion. According to Aristotle, whereas Heraclitus had said that one cannot step twice into the same river, Cratylus held that one cannot step into it even once, and in his old age he is said to have abandoned speech as a stable medium of meaning, communicating only by silently moving his finger. He gave his name to Plato's dialogue on the philosophy of language and is reported to have been Plato's first teacher.