Answer:
The "Purloined Letter" demonstrates that reality can be manipulated through lies and deceit to the extent that "reality" ceases to have a stable meaning. Dupin's dark, smoky library hints at the impenetrable nature of reality.
Step-by-step explanation:
Whereas Dupin's investigation in "The Murders in the Rue Morgue" established the basic form for a classic whodunit mystery, "The Purloined Letter" takes an entirely different route to highlight Dupin's methods of ratiocination and use of creativity to place himself in the mind of the criminal. The case is clear in that the thief and the details of the crime are perfectly obvious, but what is not clear is how to outwit the thief and return the letter to its rightful owner. The story shows much more of the character of the Prefect, who merely appeared in order to act disgruntled and embarrassed at the end of the first Dupin story. As a result, the narrative includes two characters, the narrator and the Prefect, who serve as obvious foils to Dupin, while the Minister's similarities to Dupin advance the concept of double selves that is prevalent in so many of Poe's stories.
With his energy, obvious emotions, and lack of insight, the Prefect stands in direct opposition to Dupin's calmer, more analytical approach to solving cases. His major fault is that he does not understand that the key to solving a case is to think in a way that successfully approximates the mindset of the criminal; instead, he resorts to trying to find more and more clever ways that he would personally have chosen to hide the letter while chasing answers that are increasingly further away from the correct solution. Whether the case is grisly and bizarre as in "The Murders in the Rue Morgue" or simple and clever as in this instance, Monsieur G. requires the assistance of Dupin because of his consistent inability to imagine the psyches of others. The narrator is less removed from Dupin's point of view and is more inclined to think as Dupin would, but he lacks the perception that allows him to reason out the case himself and becomes a surrogate for the reader. Because the narrator writes in the first person, he takes on the role of conveying and interpreting Dupin's brilliance for the average individual.