Slant, the Purple Dragon only tells one side of the story, and will not consider counter evidence. The people of Single Side have one ear filled with purple wax scraped from the dragon's scales. The are incapable of considering any other point of view except the "official" version from Slant or her dragon soldiers.
Notice how the mailman tries to flatter High. "wise monkey" Why does he do this? Why did he choose High as the target of his flattery?
How do real rock quarries work?
How are real amethysts mined? Where are they found?
The discussion with the innkeeper
The inn keeper doggedly refuses to understand the dragon slayer's point of view.
First he takes it as a joke.
Then the innkeeper brings up six or seven lies he believes based on partial understandings, misunderstandings, and lies. The dragon slayers try to deal with the assertions one at a time:
Jay asserts that 50% tax is too much and the innkeeper just rolls his eyes. Appeal to Ridicule fallacy (Blue)
Trudy asks for evidence of Slant's intentions and the innkeeper begs the question, by assuming what is being disputed, is not in dispute. "He sent you, didn't he?" Presumption (Red)
High pulls a fact from history to disprove the innkeeper's claim that Slant is humble. The innkeeper ignores the evidence entirely. Missing the Point (Blue)
Jay asks for evidence of Slant's protective role. Again the innkeeper refers to the disputed idea that the dragon slayers are on Slant's side as evidence. Presumption (Red)
After High insults the innkeeper, the innkeeper claims to be unhurt and then retorts passionately defending his claim that his town is the most important. He makes several arguments.
(1) Geographic centrality
(2) Two main roads crossing and going towards the points of the compass.
(3) Two essential minerals are supplied in the region.
(4) All the houses are built of stone.
His first point could have some merit, but is hardly enough by itself. Wisely or luckily the dragon slayers attack the other points. If they can isolate his point number one, they have invalidated it.
High brings up that Low Check City is much bigger, but the innkeeper counters with a good example of the impertinence of size with regard to the importance of thinking beings. Since size does matter when considering the importance of towns, it is an irrelevant fallacious argument Irrelevant Conclusion: (blue)
Pass makes a good point about the relative value of the goods in the region, but steps on her own argument by becoming too involved with an irrelevant argument of her own concerning the relative beauty of various towns. The innkeeper correctly points out the irrelevancy of the second argument while ignoring the first. Missing the point. (Blue) Pretty disappointing for the logic expert of the group, but Pass is better academically, than in actual debate.
Finally Lug notices the wax which makes the whole project impossible. The difficult journey to see Slant in person becomes unavoidable.
Battle with Slant, The Purple Dragon
Slant seems to be taken by surprise that the dragon slayers are brought into his presence as the same time as his food, and without any dragon soldiers.
Jay opens the discussion by holding Slant responsible for the lies of the dragon soldiers and the people of Single Side. This is a fallacy of presumption (Red) but might have enough supporting evidence to justify bringing it up.
Slant simply denies Jay's assertion, which is a ordinary lie. (Black)
He offers the evidence that he has not moved from his location for many months, which while probably true, is one sided because it ignores the possibility of Slant acting through agents. (Purple)
Slant at the same time tries to change the subject to Jay's sword. (Blue)
Jay quickly dismisses the sword distraction and re-begins better by holding Slant accountable for what his soldiers are saying. This is a more valid accusation then the one Jay started with.
Slant's retort is actually very good rhetoric. He is validly changing the topic to making the dragon slayers give evidence that the consequences of his lies are in some way harmful. The argument may have lasted much longer, or even had a different outcome, if he had kept going in that direction, but he gets distracted by a rhetorical trick the dragon slayer's use, albeit innocently, of asking many questions and by the circumstances of the debate.
Jay, at least, addresses the question directly by pointing out that lies are unfair, but the others pile on with a bunch of other questions, and the dragon misses the obvious reply to Jay which is, "What is unfair about it?"
Trudy goes back to holding Slant accountable for the lies of the dragon soldiers by offering evidence that they have not been delivering the "conquered" east into Slant's hands.
High wants to bring up the assertion of the inn keeper about the importance of the town of Single Side.
Slant answers by saying that it is the direction of the roads not the number of roads that is the measure of importance. Irrelevant (Blue)
Jay points this irrelevancy out, and Trudy notices that in giving his evidence Slant has acknowledged he knew what the dragon soldiers have been saying. She follows up with an accusation that the reports that Slant is a good ruler are false. Jay calls the 50% tax unfair, and Trudy piles on with a question about how Slant's future plans for Single Side. All this addresses the one-sidedness of the information that Slant has been passing out to the people.
Purple propaganda by its nature must be answered by many questions. It works by piling on a lot of one sided information. It must be unraveled by asking many questions.
The many questions and the unfavorable circumstances have upset Slant, but when he realizes they have been intentionally arranged by Fibber, Slant loses his temper. Fibber is unprotected by the magic key and exits.
Slant realizes things are not going his way and tries to make friends by claiming he has always wanted to be friends. The dragon slayers will have none of this self-contradiction and unravel it, with Pass redeeming her earlier mistakes with a very pretty point.
Then Slant tries to change the subject by attacking the Magician Key's motives. This argument should be carefully noted, because it reappears at the climax of the book. Slant's argument is actually valid, (remember logically valid does not always mean true), but Trudy catches him in a slight inaccuracy in the evidene, which because he is already upset, pushes Slant over the edge.
Conclusion
The door lost amongst the sparkles is a metaphor for loud propaganda overwhelming and hiding a quiet truth.
The people of Single Side learn that the truth, while liberating, can be painful. They become so determined to never look at only one side of something again that they rename the town Double Side and look for the other side of everything, no matter how sleight.
Jay replied, "I guess everything does have more than one side to it, doesn't it?"
Lug said, "Most things. Not everything."