“If it is any point requiring reflection,” observed Dupin, as he forebore to enkindle the wick, “we shall examine it to better purpose in the dark.”

Dupin makes this comment when the prefect first visits him and the Narrator to talk about the case. Dupin and the Narrator have been sitting in the dark, but Dupin opts not to light any candles once he learns that the prefect is visiting to ask for advice. Dupin’s preference to think in the dark ties into his larger beliefs on problem-solving. Dupin doesn’t like to get bogged down in details, that is, see too much, and instead focus only on the larger facts of a case. Thus, thinking in the dark quite literally keeps him from seeing, from focusing on anything other than the facts before him.

In the present instance I have no sympathy — at least no pity — for him who descends. He is that monstrum horrendum, an unprincipled man of genius.

Dupin has this comment to say about Minister D––’s inevitable downfall once the letter is returned to the Queen. Over the course of the story, it has become clear that Dupin and Minister D–– share similar minds. Here, Dupin draws a firm line between the two of them, distinguishing himself from Minister D–– because he has principles, implicitly using his genius for good, or at least, not evil. Furthermore, Dupin has no pity for someone who uses their genius for nefarious purposes. This comment cements that while Dupin may be eccentric and strange, he has moral boundaries that he will not cross.