Henry brought up a good point in the comment section of a post a couple of weeks ago. What do we know about the historical Socrates? Should he even be included on "greatest philosophers" lists independent of Plato?
As I said in a responsive comment at the time, we know there WAS a historical Socrates, that he wasn't simply a figment of Plato's imagination serving as mouthpiece. The other sources include: Xenophon, another of Socrates' students, who wrote his own account of Socrates' trial and condemnation; Aristophanes, the playwright who wrote a comedy with Socrates as its comic butt; and Aristotle, who referenced Socrates in ways that suggest that he was writing for an audience that still remembered the guy.
From all of this, scholars have tried to tease out what was S., what was merely the mouthpiece for P. of the same name.
The case of the Aristophanes/Socrates/Plato triangle fascinates me. If one reads THE CLOUDS, one gets a vivid picture of what Socrates looked like to those in the Athens of the day who adhered to traditional religious views and social mores. This combines nicely with Plato (and Xenophon) as one feels one is seeing the same historical figure, the center of a movement, from two sides, from both inside and outside that movement.
Make that THREE sides! A gives us Socrates from the outside. X gives us Socrates from an unimaginative admirer. P gives us the Socrates of a very imaginative admirer, who began his adult life within the movement but is going his own way.
One gets from this a sense of something Plato inherited from Socrates: the willingness to set aside customs and presumed divine commands and to ask about right and wrong, good and bad, as they reveal themselves (or fail to reveal themselves) to human reason. Philosophy until Socrates was an impersonal enterprise: what is the world made of? Water? Atoms-and-the-void?Numbers? Something else? Are time and motion realities or illusions? Socrates said: philosophy can be about ... us. The decisions we have to make, and the social context in which we make them.
Another point: why didn't Plato despise Aristophanes? The man's play may have stirred up the sentiments that led to the execution of his beloved master. What would you expect the former to think of the latter? Well, me too ... but.
But we have the SYMPOSIUM. This is Plato's great examination of the question of "love" in philosophy. The character "Aristophanes" (who seems straightforwardly drawn from life) plays a big part in this dialog and in fact many readers come away from it inclined to accept the view of love Plato attributes to Aristophanes rather than that he gives to Socrates. Plato would seem to respect Aristophanes. If he was giving us an account of actual views on love that were in fact congruent with Aristophanes' thinking, then he was also phrasing them moire-than-fairly, eloquently and persuasively.
One gets a sense here of three geniuses in a complicated triangular relationship. Hence the triangle above.
As for such questions as: did Socrates have a theory of abstract Form, and did he see that theory as a vindication of the possibility of knowledge? Would he have agreed with his semi-fictional alter ego that he was trying to encourage humanity to tear itself away from shadows on the cave wall so they can contemplate realities, both behind them within the cave and outside the cave altogether? I must leave such questions open. There isn't even a beginning of scholarly consensus on them. But I can see that many philosophers, committed to various views of Socrates' role, would naturally want him on such a list in his own right.