(Κρατύλος), a Greek philosopher, and an elder contemporary of Plato. He professed the doctrines of Heracleitus, and made Plato acquainted with them. (Aristot. Met. 1.6 ; Appul. de Dogmat. Plat. p. 2, ed. Elm.; Olympiod. Vit. Plat. p. 79, ed. Fischer.) The time at which Plato was instructed by Cratylus, is stated by Diogenes Laertius (3.6) to have been after the death of Socrates; but there are several circumstances which prove that Plato must have been acquainted with the doctrines of Heracleitus at an earlier period, and K. F. Hermann has pointed out that it must have been in his youth that Plato acquired his knowledge of that philosophy. One among the dialogues of Plato is named after his master, Cratylus, who is the principal speaker in it, and maintains the doctrine, that things have received their names according to certain laws of nature (φύσει), and that consequently words correspond to the things which they designate. Hermogenes, the Eleatic, who had likewise been a teacher of Plato, asserts, on the other hand, that nature has nothing to do with giving things their suitable names, but that words are applied to certain things by the mere mutual consent (Δέσει) of men. Some critics are of opinion, that the Cratylus introduced by Plato in his dialogue is a different person from the Cratylus who taught Plato the doctrines of Heracleitus, but the arguments adduced in support of this opinion do not seem to be satisfactory. (Stallbaum, de Cratylo Platonico, p. 18, &c.; K. F. Hermann, System der Plat. Philos. i. pp. 46, 106, 492, &c.; Lersch, Sprachphilos. der Alten, i. p. 29, &c.)