Ion

Ion is a rhapsode -- a professional reciter of poetry -- who specializes in Homer.  And he's portrayed as a bit dippy.  In this short dialog, Socrates doesn't engage in argument with him so much as simply tell him what to think.  Ion claims that Homer is the greatest poet.  Stop me if you've heard this question before but ... how is it that Ion is given to know that Homer is the greatest poet?  What is a rhapsode really a master of that would enable him to make this evaluation?  

The question is inconvenient for Ion because it turns out that he knows nothing about the contents of those subjects Homer discusses in the Iliad and the Odyssey.  Ion doesn't know whether Homer's description of how to drive a chariot is a good one, or whether the home remedies he shows characters taking would actually work, or whether the fishing techniques he depicts actually catch fish.  For these questions, you would need to consult a charioteer, a doctor, and a fisherman respectively.  In fact, Ion can't come up with any particular thing that the rhapsode knows.  Even his contention that, having memorized all of Homer, he at least knows how different people should speak, founders on an argument we saw in Gorgias -- to know if someone is speaking well, you have to know something of what they are speaking about.  Finally, Ion claims that since he knows so many speeches made by generals, he knows how to be a general.  Technically, this last contention goes unrefuted by Socrates, but is clearly meant as a reductio ad absurdum type of joke.

You might say that this argument seems to miss the point.  You don't need to be an expert on whales, after all, to appreciate that Moby Dick is a great novel.  So why can't we say that Ion's expertise is not related to the contents of poems, but to their forms?  The dialog doesn't really deal well with this question.  The closest it comes to explicitly treating the form of poetry is a brief early passage where we discover that while Ion recites other poetry, most of it bores him, and he only claims to really know how great Homer is.  Socrates takes this to indicate that the rhapsode is really not a master of anything like the evaluation of the form of poetry.  Have you ever heard of the master of a subject only being able to venture an opinion on one exemplar of it?  A master painter or sculptor would know whether any painting or sculpture was valuable, not just whether Picasso's qualified.  It's a fair argument, but I think we still come away from the dialog wondering if Socrates has addressed poetry itself as an art form over and above the mere contents of a poem.  

Or perhaps the lack of focus on the form of poetry is deliberate, and is meant to allow a special place for a 'formal' understanding, one that would be orthogonal to the type of argumentative understanding Socrates calls knowledge or mastery.  In a sense, this might fit with the glimpses we've seen of Plato's later works.  Phaedo and Gorgias (and I think we'll see many if not all of the later dialogs) end with a myth.  There's no myth in Ion, but perhaps Socrates is setting the stage.  Here, he says that while Ion is not a master of any profession, he can say all sorts of interesting things about Homer because he is divinely inspired.  Given how daft Ion seems, it's hard to read this as a compliment exactly, but Socrates doesn't seem to mean it in a derogatory sense either.  Divine inspiration may not be mastery, but it's not worthless either, so long as we understand what it is and is not.  Socrates illustrates his claim with a beautiful metaphor about magnets (which come from Magnesia, it turns out).

As I said earlier, that's not a subject you've mastered—speaking well about Homer; it's a divine power that moves you, as a "Magnetic" stone moves iron rings. (That's what Euripides called it; most people call it "Heraclean.") This stone not only pulls those rings, if they're iron, it also puts power in the rings, so that they in turn can do just what the stone does—pull other rings—so that there's sometimes a very long chain of iron pieces and rings hanging from one another. And the power in all of them depends on this stone. In the same way, the Muse makes some people inspired herself, and then through those who are inspired a chain of other enthusiasts is suspended. You know, none of the epic poets, if they're good, are masters of their subject; they are inspired, possessed, and that is how they utter all those beautiful poems. The same goes for lyric poets if they're good: just as the Corybantes are not in their right minds when they dance, lyric poets, too, are not in their right minds when they make those beautiful lyrics, but as soon as they sail into harmony and rhythm they are possessed by Bacchic frenzy. (533d)