Don Quixote is about who decides what a scene is, and what one pays for disagreeing. A gentleman sees giants where there are windmills and a castle where there is an inn, and for every refutation he has an enemy magician who explains the defeat without correcting the vision. The book does not ask whether he has gone mad, which the first chapters already say; it asks who sustains, denies, or fabricates what he sees.
In Part One, the price appears on stage, and the one who pays, generally, is not him. Andrés pays, who is beaten again after his liberator goes away; the muleteer pays, with his head split open on the night of the arms; Sancho pays, tossed into the air in a blanket. Sancho is the measure of the real: when his master explains the beating as the work of an enchanted Moor, he replies that what cannot be seen can be felt, and that his back should be the judge.
Part Two changes the question. Ten years later, everyone has read Part One: the bachelor, the dukes, the inn guests, and even a false Don Quixote. It is no longer enough to know whether the gentleman sees what exists; one must know who fabricates what he expects to see. Sancho, who was the measure of the real, becomes the author of the illusion, for it is he who invents the enchantment of Dulcinea.
Around this, the book fits in other subjects: the freedom of Marcela, who says she was born free, the justice of the galley slaves and that of Sancho's governorship, the love the gentleman feels for a lady he knows only by hearsay, and the question of how a story is told, with an Arab historian of doubtful authority and an author who quarrels, within the book, with his false continuator.