"Miracles, upon my soul!" rejoined Gringoire. "Here the blind see, and the lame run." (II.VI.25)
The Cour des Miracles, or the Court of Miracles, is a bit of a tongue-in-cheek name. Gringoire is pointing to that here: it's a "miracle" that the blind should suddenly be able to see, but the reason they do is that they're all criminals faking blindness in the first place. The suggestion is that deception, or rational misunderstanding, underlies many (all?) "miracles." But "Court of Misconceptions" somehow just doesn't have the same ring to it.
The people held much the same opinion; all who possessed any wisdom regarded Quasimodo as the demon and Claude Frollo as the conjurer. It was obvious that the bell ringer had been engaged to serve the Archdeacon for a specific time, at the expiration of which he would be sure to steal his soul by way of payment. (IV.V.9)
The best part of this passage is the narrator's statement that "it was obvious…" You know why? Because it's not obvious at all. This is Hugo at his most bitingly sarcastic. Naturally "all who possessed any wisdom" would come to the conclusion that Frollo called forth a deformed demon to be his servant in exchange for his soul, right? It makes perfect sense. Hugo is trying to give you a sense of the superstitious mentality of this society. These people love accounting for things with weird supernatural logic.
"The next day, which was Sunday, they found on a heath between Gueux and Tilloy, about two leagues from Reims, the remains of a large fire, a few ribbons that belonged to Paquette's child, and several drops of blood and goat droppings. There could be no further doubt that the gypsies had Saturday night held their Sabbath on this heath and devoured the child in the company of their master, Beelzebub, as is the custom among Mahometans." (VI.III.52)
Like the passage above, Hugo doesn't literally believe that based on this evidence, "there could be no doubt" about the child being eaten. He's taking on the voice of the superstitious people. In their minds, there can be no other explanation, but we, as readers, are meant to see what a ridiculous leap in logic this is. The people's lack of logic gets reinforced by their other misunderstandings about gypsies, as well, and those are on full display all through the novel. For example, did you know that gypsies worship the demon Beelzebub? Or that they are Muslims? Or that they come from Egypt? Nice try, Parisians, but we're so not buying it.
"Oh!" she stuttered, in a tone of anguish, covering her face with both her fair hands. "She is a sorceress!" All the while a voice cried bitterly in the depth of her heart—"She is a rival!" She sank fainting to the floor. (VII.I.118)
This is a perfect example of how the characters in the novel use sorcery as an excuse to hate on people they just don't like—usually for totally unrelated reasons. We're not saying that Fleur-de-Lis doesn't actually believe that Esmeralda is a sorceress, but we are saying that her accusations are motivated by a deeper desire to eliminate Esmeralda as a competitor for Phœbus's affection. Unfortunately, she's not alone in using accusations of witchcraft as an excuse to mask another desire: Frollo does the same thing.
"Pure magic, Master Jacques!" he exclaimed. "Emen-Hétan—that is the cry of the witches on their arrival at their Sabbath meetings. Per ipsum, et cum ipso, et in ipso—that is the command that chains down the devil in hell. Hax, pax, max—that belongs to medicine, a remedy for the bite of rabid dogs." (VII.V.13)
If only rabies could be cured with a chant. This passage shows us where Frollo falls on the superstitious scale: pretty high up there. As readers, we're supposed to see his earnestness as ignorance, but we're also supposed to get a sense of what sort of guy we're dealing with. Hint: a hot mess (except not actually hot). Frollo takes this stuff seriously, and he's part of a society that also takes it seriously. That means that rather than being some crazy guy muttering spells to himself up in a tower, he's able to wield some major clout when it comes to the justice system. Yeah. We smell trouble brewing.
"The specter, the goat, and all that, look very much like sorcery," said Gringoire to a neighbor. "Oh yes, and the withered leaf," added another. "No doubt," observed a third, "it was a witch working with the goblin-monk to rob the officer." Gringoire himself could scarcely help thinking that there was some probability in the conjecture. (VIII.I.30)
It's important to recognize that this scene is meant to be funny. It's partly because we have seen how the whole affair with the leaf actually went down, but it's also partly because everyone is so willing to see sorcery as an explanation for everything.
Nothing was more common in those days than to indict animals for sorcery. (VIII.I.53)
This little tidbit might just seem like a ridiculous aside at first, but it actually shows us how convenient is to accuse people of sorcery: people accused of sorcery can't really prove otherwise, can they? This is doubly true for animals, who literally can't argue in their defense—or even understand that they are being indicted, for that matter.
Jacques Charmolue, by shifting the tambourine in various ways, made the goat exhibit several other tricks with regard to the day of the month, month of the year, and so forth, which the reader has already witnessed; and, from an optical delusion peculiar to judicial proceedings, the very same spectators, who had perhaps many a time applauded the innocent pranks of Djali in the streets, were horrified by them within the walls of the Palace of Justice. The goat was decidedly a devil. (VIII.I.57)
There is definitely some hypocrisy involved when it comes to the mob mentality of a witch hunt. Basically, you can attach a supernatural explanation to just about anything if you feel like it. That's exactly the point: it's a matter of perspective. Without the accusation of sorcery, it's easy to see Djali's tricks as… tricks. The crowd, however, is more concerned with seeing the workings of the devil. It makes things more exciting that way. It also makes all of them feel safe. None of them has a trick-playing goat like that, so if a trick-playing goat is a sign of sorcery, then they're safe.
"At the moment when these thoughts were crossing my brain I saw near her a goat, a beast that one associates with witches. It looked at me and laughed. The noontide sun tipped the goat's horns with flame. Then I perceived the demon's trap, and had no further doubt that you were from hell, and had come for my perdition. I believed it." (VIII.IV.50)
It's convenient for Frollo that Esmeralda has a pet that tends to be associated with the devil (for its horns and hooves and whatnot; the devil was often imagined as being part goat). Maybe a dog or a pot-bellied pig would have been a safer option.
He imagined that more magic than love was mixed up in it, and there was probably a sorceress, perhaps the devil who had gotten involved. (VIII.VI.3)
It's so easy to just use sorcery as an excuse for everything, isn't it? That's certainly true for someone like Phœbus, who doesn't like to hurt his pretty head with too much thinking. Otherwise, he might have to find an explanation for the weird stuff that happened, and that's just too much trouble. Sorcery's a nice quick fix of an explanation. Maybe that's why the justice system loves it so much.