Cratylus

Cratylus (ancient Greek: Κρατύλος, Kratylos) was an ancient Athenian philosopher from late 5th century BC, mostly known through his portrayal in Plato's dialogue Cratylus. Little is known of Cratylus or his mentor Heraclitus (of Ephesus, Asia Minor). According to Cratylus at 402a, Heraclitus proclaimed that one cannot step twice into the same stream. According to Aristotle (Metaphysics, 4.5 1010a10-15), his disciple Cratylus went a step further to proclaim that it cannot even be done once. Such was his thorough-going skepticism.

If the world was in such constant flux that streams could change instantaneously, then so could words. Thus, Cratylus found communication to be impossible. As a result of this realization, Cratylus renounced his power of speech and limited his communication to moving his finger. He was an advocate of the idea that language is natural rather than conventional. The little known philosophy of Cratylism is based on "reconstituted" teachings, owing mostly to Cratylus's and Heraclitus's inclusion in the Dialogues of Plato.