Little is known of Cratylus beyond his status as a disciple of Heraclitus of Ephesus, Asia Minor. The modern biographical tradition has not reached consensus on his approximate date of birth, arguing alternately for an age comparable roughly either to Plato or Socrates. Cratylus is mentioned in Aristotle's Metaphysics in a passage which seems to imply that Cratylus was an established and active philosopher in Athens during the mid-late 5th century, and that Plato himself became briefly interested in his work prior to aligning with Socrates.
In Cratylus' eponymous Platonic dialogue, the character of Socrates states Heraclitus' proclamation that one cannot step twice into the same stream. According to Aristotle, Cratylus went a step beyond his master's doctrine and proclaimed that it cannot even be done once. The contemporary philosophy Cratylism is based on a reconstructed version of Cratylus' theories of flux and language as they appear in Plato's dialogue and has been influential to Eastern thinkers, including Buddhistsemioticians.