[SnakePlissken]

It's an understandable mistake (if it was one), as Plato wrote most of his works as dialogues between Socrates and other Athenians (including Republic, where the Allegory of the Cave originates).

From another angle, the paragraph in reference is a summary of what the article's author believes the author of the book being reviewed alleges is the macro-narrative in regards to philosophy as presented today and understood by philosophy-averse intellectuals. As the article-author explicitly mentions Plato later in the article (in reference to an earlier work by the book-author extolling Ancient Greek philosophy) and distinguishes between the ideas of Plato and Aristotle, it seems impossible that either author doesn't realize the Cave isn't Socrates' idea. Although sloppy, it seems that the article-author is simply implying that there is so little familiarity with the full breadth and depth of philosophy that the average individual with passing knowledge of the ancients might know of the Allegory of the Cave/theory of the Forms/etc but would wrongly attribute it to Socrates as he is the mouthpiece in Republic.

[sverige]

Well, wait a minute. The Eleusinian mysteries were ancient by the time that Socrates was mentoring Plato. Plato was just the first to write this stuff down. How do we know that Plato wasn't reporting what Socrates taught him? And, if true, how can we be sure that Socrates didn't get the idea from someone else?

[1] https://en.m.wikipedia.org/wiki/Eleusinian_Mysteries

[hyperpape]

There is a lot of work that traces developments in Plato's ideas, and a rough consensus that some dialogues are more Socratic and others reflect Plato more (http://plato.stanford.edu/entries/plato/#HisSocEarMidLatDia). There's a mixture of stylometrics, contemporary accounts, and other arguments that are used to try and assign responsibility. It's an inherently imprecise project, and I didn't do much ancient philosophy so I can't tell you much about it, but it seemed sensible when I took courses on Plato.

[SnakePlissken]

>How do we know that Plato wasn't reporting what Socrates taught him? And, if true, how can we be sure that Socrates didn't get the idea from someone else?

Quite plainly, we don't know. It seems irrelevant, however, as the line of inquiry was about whether the article-author mistakenly attributed the Allegory of the Cave to Socrates when the 'correct' attribution is to Plato (that is, the established/agreed-upon/canonical attribution), not whether or not the Allegory is a wholly original, purely inspired, spontaneously birthed thought from Plato.

In regards to the ideas truly being Socrates' or those of a precedent, I'm aware of nothing that indicates that being the case (other than the standard A influences B influences C, etc, nature of philosophy). I'm no expert, but it seemed clear to me in reading Plato's work after the death of Socrates (e.g., Republic) that he is radically departing from the views of his teacher. If the counterpoint is that Plato received all of this wisdom from Socrates, then attributed the introductory bits to his teacher and kept the juiciest for himself, we know that's not the case: many other contemporaries wrote about the views of Socrates and some even recorded Socratic dialogues.

In Republic, Plato advocates things like an elite intellectual class that actively deceives the hoi polloi and prevents them from accessing philosophy, yet Socrates was put to death for his repeated attempts at engaging all Athenians who would listen in philosophical debates. Socrates warned against the youth of Athens losing their ability to think critically, while Plato advocates a utopian system predicated on the vast majority of its citizens not questioning things at all. In fact, it's frequently suggested that Plato's dramatic departure from the Socratic notion of "I know nothing" and the near-totalitarian features of his Republic are direct results of the Athenians turning on and executing Socrates. The entire idea of a Philosopher King and an enlightened ruling class micromanaging the lives of the producer/worker and guardian/soldier classes seems like a plan to ensure that no great thinker ever suffers the same fate as Socrates. With the rebellious and reactionary nature of the Republic established, it seems clear he didn't get the ideas contained within from Socrates. This seems especially true because Plato does not discuss them until ~380 BC, almost two decades after the death of Socrates. If he inherited or stole the ideas, why wait so long to talk about it? And why didn't anyone else know about it (Plato was one of several students who followed Socrates)?

I've glanced, very lightly, over the Wikipedia page for the Eleusinian Mysteries, and there's nothing specific leaping out at me as inspiration for the Allegory of the Cave (other than the idea of a layered underworld, but that's not unique to the Mysteries or particularly reflective of the Cave). I'm unfamiliar with these ideas; can you expound upon the connection, or is the argument just that because the Mysteries were ancient and once orally disseminated, there's a chance that the Allegory was too and merely reported by Plato as original?