Plato's Republic, Shortened

  So there's this guy named Thrasymachus. He's disgusting, odious, always stuffing his face and belching, because that's what sophists do. He's like, "Socrates, you think you're so clever. But you know what I think? I think morality is just a social construct determined by whoever holds power in a given society." And Socrates is like, "Oh, you do, do you? Well, I'm just a humble teacher, what do I know about anything? But first, how do you define morality? How are you defining virtue? How are you defining vice? And by following through the logical consequences of those terms, haven't you just said that vice is a virtue and virtue a vice and thereby lost yourself in a welter of contradictions?" "Alright, you win this round, Socrates," says Thrasymachus. He exits stage left, in tears. 

Glaucon and a bunch of other people are like, "Ha ha, good one, Socrates. You sure showed him. But seriously. Trolling the sophists is always good fun. Owning Thrasymachus is always good sport. But can you tell us: what's the actual answer? How do we know morality isn't just a social construct again? Do you have an argument that isn't just based on semantics, tautologies, and definitions?" Then Socrates is like: "Well, I'm just a humble teacher. What do I know about anything? But, we can definitely say this much: the human soul must be a lot like a city." 

Glaucon and others: "Of course!" "Naturally." "That follows." "How could it be otherwise?"

Then Socrates is like: "And a city would need to be ruled by its smartest people. That's us. Of course, we'll have to put one over on the rubes so that they'll do what we say. We'll tell them they were born this way. Also, we need to take away everyone's children and raise them collectively so they are loyal only to the state and not to their parents. Also, we need to suppress the arts."

Glaucon and others: "Of course!" "Naturally." "That follows." "How could it be otherwise?"

Socrates: "Also, many people will not understand you, because you have glimpsed the higher truths. You're like somebody who's seen the sun trying to explain what it's like to a bunch of people who have been trapped in darkness their whole lives."

Glaucon et al.: "Quite so." "Naturally." 

Socrates: "Also, this cool thing will happen when we die where we will be reincarnated and we will be lined up in front of this thing and there will be a whole decision process about what our next lives will be like and it will be awesome. And so, in short, we know that tyrannical and immoral people are ruled by their baser appetites, just like how poorly-governed cities are run by stupid and poor people. Therefore, morality has an objective basis that is not just socially defined. QED."