The best chess-player in Christendom may be little more than the best player of chess; but proficiency in whist implies a capacity for success in all these more important undertakings where mind struggles with mind. When I say proficiency, I mean that perfection in the game which includes a comprehension of all the sources whence legitimate advantage may be derived. These are not only manifold, but multiform, and lie frequently among recesses of thought altogether inaccessible to the ordinary understanding. (2)
The key to this ideal analytical/creative whist brain is that bit about the "[lying] frequently among recesses of thought altogether inaccessible to the ordinary understanding." What we have here is awe before the human mind itself, which can think, but which has trouble thinking about how it thinks. What makes Dupin so fabulous is that he is able (symbolically, at least) to meet and do battle with those "recesses of thought altogether inaccessible." After all, what is the Ourang-Outang if not a giant, ape-shaped symbol of our irrational, repressed instincts?
"Dupin," said I, gravely, "this is beyond my comprehension. I do not hesitate to say that I am amazed, and can scarcely credit my senses. How was it possible you should know I was thinking of -- -- ?" Here I paused, to ascertain beyond a doubt whether he really knew of whom I thought. (14)
Here it is, practically an engraved invitation to Dupin to spend about a page and a half on the amazing workings of his own mind. Without the encouragement of the narrator's astonishment and confusion, Dupin would have no plot-related reason to reveal his logic, and we'd have no story.
"But it is by these deviations from the plane of the ordinary, that reason feels its way, if at all, in its search for the true. In investigations such as we are now pursuing, it should not be so much asked `what has occurred,' as `what has occurred that has never occurred before.' In fact, the facility with which I shall arrive, or have arrived, at the solution of this mystery, is in the direct ration of its apparent insolubility in the eyes of the police." I stared at the speaker in mute astonishment." (59-60)
Not only are there two kinds of human mind according to Dupin, but there also appear to be two kinds of criminal cases: the obvious kind that the police are pretty good at, and the difficult kind that they can't seem to solve. It's exactly the irrationality of these murders that make Dupin so particularly suited to them. Which raises the question, what does Dupin do with the little questions of his everyday life? Does he stare fixedly at the narrator throughout the day trying to deduce, we don't know, what he had for breakfast?
"How was it possible," I asked, "that you should know the man to be a sailor, and belonging to a Maltese vessel?"
"I do not know it," said Dupin. "I am not sure of it. Here, however, is a small piece of ribbon, which from its form, and from its greasy appearance, has evidently been used in tying the hair in one of those long queues of which sailors are so fond. Moreover, this knot is one which few besides sailors can tie, and is peculiar to the Maltese. (97-98)
So it's not all just reasoning. The narrator's amazement draws out evidence that Dupin needs supplemental knowledge to make his claims, knowledge like this bit about Maltese knots. In the midst of the narrator's points about different kinds of human intelligence, where does sheer knowledge fit in?
"I don't mean that you should be at all this trouble for nothing, sir," said the man. "Couldn't expect it. Am very willing to pay a reward for the finding of the animal — that is to say, any thing in reason."
"Well," replied my friend, "that is all very fair, to be sure. Let me think! — what should I have? Oh! I will tell you. My reward shall be this. You shall give me all the information in your power about these murders in the Rue Morgue.
Dupin said the last words in a very low tone, and very quietly. Just as quietly, too, he walked toward the door, locked it, and put the key in his pocket. He then drew a pistol from his bosom and placed it, without the least flurry, upon the table. (111-113)
Here, we see the effect of Dupin's sudden flights of insight on someone who isn't familiar with his methods. Dupin's insight strikes him like a blow: the sailor's face "flushed up as if he were struggling with suffocation." How does this physical response on the part of the sailor affect our own feelings about Dupin's genius? Are you impressed? Impatient? What is your reaction?