12. The Republic - Plato

I'm not going to lie. This was incredibly difficult to read. Even more so than Shakespeare! I wish I had read this in a philosophy class, so I could have had a professor help me along with it. His style is sort of like Descartes' (more accurately, Descartes' is like his) in that he proposes different theories and eliminates the ones that don't work until whatever does work is remaining. It's written in the form of a dialog.
Part of this book was Plato's attempt at defining justice. As an attorney, I should have been really feeling that ... but for much of the book, although my eyes were moving, I had no idea what I was reading. He proposes the ideas of returning debts owed, and helping friends while harming enemies - but ultimately concludes that those definitions are inadequate in some situations.
He then moves into discussing justice in the city (i.e. government), which Socrates (remember, it's written as a dialog) suggests may help them see justice in the person, but on a larger scale.
Plato also asserts that the power of wisdom is possessed most abundantly in kings and philosophers, and that others should accept the authority of those wise and morally superior leaders.
Again - this is of course a classic, but it'd be best to read it with a philosophy professor (or maybe a "morally superior leader").