The two principal interlocutors are Simmias and Cebes, the disciples of Philolaus the Pythagorean philosopher of Thebes. Simmias is described in the Phaedrus as fonder of an argument than any man living; and Cebes, although finally persuaded by Socrates, is said to be the most incredulous of human beings.
It is Cebes who at the commencement of the Dialogue asks why 'suicide is held to be unlawful,' and who first supplies the doctrine of recollection in confirmation of the pre-existence of the soul. It is Cebes who urges that the pre-existence does not necessarily involve the future existence of the soul, as is shown by the illustration of the weaver and his coat.
Simmias, on the other hand, raises the question about harmony and the lyre, which is naturally put into the mouth of a Pythagorean disciple. It is Simmias, too, who first remarks on the uncertainty of human knowledge, and only at last concedes to the argument such a qualified approval as is consistent with the feebleness of the human faculties.
Cebes is the deeper and more consecutive thinker, Simmias more superficial and rhetorical; they are distinguished in much the same manner as Adeimantus and Glaucon in the Republic.
Other persons, Menexenus, Ctesippus, Lysis, are old friends; Evenus has been already satirized in the Apology; Aeschines and Epigenes were present at the trial; Euclid and Terpsion will reappear in the Introduction to the Theaetetus, Hermogenes has already appeared in the Cratylus. No inference can fairly be drawn from the absence of Aristippus, nor from the omission of Xenophon, who at the time of Socrates' death was in Asia. The mention of Plato's own absence seems like an expression of sorrow, and may, perhaps, be an indication that the report of the conversation is not to be taken literally.