A son of Hipponicus, and a brother of the wealthy Callias, is introduced by Plato in his dialogue Cratylus as one of the interlocutors, and maintains that all the words of a language were formed by an agreement of men among themselves. Diogenes Laërtius (iii. 6) states that he was one of the teachers of Plato, but no other writer has mentioned this, although there was no want of opportunities; and it is further clear from the Cratylus, that Hermogenes was not a man either of talent or learning, and that he scarcely knew the elements of philosophy. Although he belonged to the great family of Callias, he is mentioned by Xenophon as a man of very little property: this is accounted by some by the supposition that Hermogenes was not a legitimate son of Hipponicus, but only a nothos. Plato (Cratyl. p. 391, c.), on the other hand, suggests that he was unjustly deprived of his property by Callias, his brother. (Comp. Xenoph. Memor. ii. 10. § 3, Conviv. i. 3, Apol. 2; Groen van Prinsterer, Prosopogr. Plat. p. 225; C. F. Hermann, Gesch. u. System der Plat. Philos. i. pp. 47, 654.)