Book I is a play.

Which translation? It matters more here than for almost anything else on this site, and the person who tells you it doesn't has read one. I've taught from Grube and Reeve for years and I'd send anyone there first: the Greek is served plainly, the notes are short, and Thrasymachus swears properly. Jowett is beautiful and Victorian and quietly makes Socrates sound like a bishop. Bloom is accurate, unreadable, and arrives with an interpretive essay longer than several of the books it interprets.

So. Seven.

Book I is astonishing and everybody knows it. It's a genuine drama: a dinner party going wrong, an old man edging out of the room, a bully shouting, an argument won on a technicality that Socrates himself doesn't seem entirely happy about. Had Plato written twenty of those he'd be a dramatist and we would read him for pleasure.

Then Book II happens, Glaucon and Adeimantus hand Socrates the floor, and he does not give it back until Book X. What follows is one of the two or three most consequential arguments ever set down and it is also, page by page, a man agreeing with himself. "Certainly, Socrates." "It seems so." "How could it be otherwise?" The interlocutors stop being people somewhere in Book IV and become punctuation.

I don't hold the totalitarian charge against it the way Popper did. Popper was writing in 1945 and reading a fifth-century text as though it were a manifesto submitted to a committee, and there's a category error buried in that. What I do hold against it is the tone: the calm with which the poets are expelled, the calm with which children are removed from parents, the calm with which the noble lie is proposed and nobody at the table blinks. That calm is the thing worth arguing about, and students always want to argue instead about whether the ideal city would be pleasant to live in, which is not the question.

The cave is in Book VII and it is as good as its reputation, which is rare. The divided line just before it is not, or rather it is good but so compressed that no undergraduate of mine has ever got it from the text alone, and I include myself at twenty.

A practical note. Buy an edition that prints the Stephanus numbers in the margin, because every piece of scholarship you will ever read cites them, and an edition without them makes you useless in a seminar. Oxford World's Classics does this. Several cheaper reprints don't, and one of them, which I won't name because I've thrown it out, silently drops a chunk of Book X.

I go back about every four years, usually because somebody has said something confident about justice at a dinner and I've realised I can't actually reconstruct the argument. Then I read Book I with pleasure and Books V through VII with effort and I stop somewhere in VIII, having got what I came for.