Do we only know what Socrates taught thru the writings of Plato? If so… was Socrates real? Were the other speakers in the dialogues real?
We have no writings from Socrates, himself. The dialogues are all from Plato. Socrates is also written about by Xenophon and Aristophanes, so he was a real person. The other characters in Plato’s dialogues are probably a mixture of real and fictional people. It is hard to say for sure, though, what are the actual words of Socrates and what is Plato’s.
Probably many of the other characters in the dialogues (esp. the early ones) are real – Parmenidies certainly was, and I think we have independent evidence for the existence of some of the other students like Crito, IIRC.
It’s been many years since I studied Plato but my recollection is that scholars see three periods in his work. The early work is mostly Plato trying to illustrate the beliefs of his teacher. The middle dialogues show more of Plato’s own philosophical beliefs espoused by the character of “Socrates,” and the latest works are fully Plato’s own, although still in dialogue form.
–Cliffy