2. The son of Ariston, and brother of Plato, who, besides mentioning him elsewhere, makes him one of the speakers in the republic. He is also introduced as a speaker in Xenophon's Memorabilia (3.6). Suidas (s. v. Πλάτων) calls him Glaucus. (See also D. L. 3.4; Plut. de Frat. Amor. p. 484e.) In Plato's Parmenides also, Glaucon is one of the speakers; but a doubt has been raised whether this is not a different person, on the ground of an anachronism which the passage contains. Considering, however, the frequency of anachronisms in Plato, it sees most probable that this Glaucon is his brother. (Comp. Heindorf. ad Plat. Parmen. p. 126.) There is, perhaps, more doubt about the Glaucon who is one of the speakers in the (p. 172c.).

It is universally believed that this Glaucon is the Athenian philosopher mentioned by Diogenes Laertius, as the author of a book containing nine dialogues, entitled, Φειδύλος, Εὐριπίδης, Ἀμύντιχος, Εὐθίας, Λυσιθειδης, Ἀριστοφάνης, Κέφαλος, Ἀναξίφημος, Μενέξενος. Thirty-two other dialogues, which were ascribed to him, are designated as spurious by Diogenes (2.124).

The following pedigree represents the relationships above referred to:--