... I'm not finished with Kahn's book, but I find the central thesis fascinating. I had not considered it before. Almost everyone seems to believe that Plato's philosophy developed over time. It seems possible to construct a time line of dialogues with the "early" ones representing Socrates more than the later ones.
Who before Kahn has ever suggested an "ingressive" approach, where Plato's philosphy is fully-formed, but only revealed in pieces? Perhaps others, I do not know. But I think the model Kahn suggests opens up a whole line of thinking about Plato. So Plato didn't discuss "recollection" in the Meno without having the fully fledged idea of Forms in mind. I've always had the impression that scholars were saying that Plato's doctrine of "recollection" was the most advanced position he had at that time, as if "Forms" hadn't occured to him yet.
Anyway, I like where Kahn is going. He may not be expressing the "common opinion," but he is correct to tie the literary qualities in with the philosophy. ... I could be wrong.
I had written a lengthy review of this work but, since it has never appeared on this site, I will attempt to reprise it in a more condensed version. Charles Kahn is a highly respected scholar of ancient philosophy at the University of Pennsylvania. Unfortunately, this book does him no credit and actually calls into question his very ability to read Plato. Put as broadly as possible, Kahn sees the platonic corpus as an attempt by Plato to gradually educate his readers in his doctrines. The progress he traces is from the "earliest" works (eg. the Apology) to the Republic, which he regards as the fullest revelation of Plato's teachings. To that end he proceeds to ransack every dialogue within this period for indications of a "developmental" approach by Plato. Differences between dialogues are papered over or fobbed off on the vague assertion that Plato wasn't engaged in a coherent discussion of the topic-in-question at this point in his writings because he didn't believe that his readership could understand it. Essentially Kahn has inverted the usual "developmental" approach to Plato (ala Gregory Vlastos) by assuming that Plato's writings evolved while his philosophy did not. While this assumption is preferable it does not aid Kahn in his interpretation.
This book is a classic example of a scholar letting his critical apparatus (and prejudices) get in the way of the necessary task of sustained, careful exegesis. Kahn has absolutely no "feel" for the "literary" elements of the dialogues and he cannot give any reasons for the fact that Socrates's discussions are different when he is speaking with different interlocutors. Kahn ignores very important details for the sake of his pet thesis and it is invariably those details which disprove Kahn's readings. Why does Diotima lecture Socrates about eros in the "Symposium" but it is Socrates who does the lecturing in the "Phaedrus?" Kahn is incapable of asking or answering this question. Plato was a writer of considerable comedic talents but Kahn pays little or no attention to this. He is also enamored of making embarassing statements about Plato being a "mystic" and a "metaphysician" who is not interested in the everyday world. As Kahn never defines what a "mystic" would be it is very difficult to know whether he is referring to Madame Blavatsky or Plotinus. In addition, Plato's consistent engagement with politics and its relationship to philosophy disproves such assertions. Furthermore, Kahn's dismissal of Xenophon as "unphilosophical" raises the question of whether the ivy-league professor is being careless or just incompetent. Recent work on Xenophon has revealed a thinker of subtle complexity who was well regarded by men such as Cicero, Machiavelli, and Sir Philip Sidney. Kahn's inability to understand Xenophon is one in a series of grave flaws which capsize this work. Put as baldly as possible, this is a bad book--perhaps the worst I have read in several years--which should never have been published. The hypothesis is absurd and the analysis very shoddy. What other readers seem to interpret as "boldness" is really just zealous belief in a questionable interpretation (ie. monomania). Plato is far too subtle a thinker and writer for Kahn to grasp so the professor decided to construct an effigy of Plato which he then sets alight, believing that it is the real thing. Avoid this work at all costs and, instead, spend your money on Sayre's "Plato's Literary Garden" or Sallis's "Being and Logos" where you will be treated to a wonderfully complex discussion about the ancient sage and his writings.