I was astounded. The Prefect appeared absolutely thunderstricken. For some minutes he remained speechless and motionless, less, looking incredulously at my friend with open mouth, and eyes that seemed starting from their sockets; then, apparently in some measure, he seized a pen, and after several pauses and vacant stares, finally filled up and signed a check for fifty thousand francs, and handed it across the table to Dupin. The latter examined it carefully and deposited it in his pocket-book; then, unlocking an escritoire, took thence a letter and gave it to the Prefect. This functionary grasped it in a perfect agony of joy, opened it with a trembling hand, cast a rapid glance at its contents, and then, scrambling and struggling to the door, rushed at length unceremoniously from the room and from the house, without having uttered a syllable since Dupin had requested him to fill up the check.
When he had gone, my friend entered into some explanations.
“The Parisian police,” he said, “are exceedingly able in their way. They are persevering, ingenious, cunning, and thoroughly versed in the knowledge which their duties seem chiefly to demand. Thus, when G— detailed to us his mode of searching the premises at the Hotel D — I felt entire confidence in his having made a satisfactory investigation — so far as his labors extended.”
“So far as his labors extended?” said I.
“Yes,” said Dupin. “The measures adopted were not only the best of their kind, but carried out to absolute perfection. Had the letter been deposited within the range of their search, these fellows would, beyond a question, have found it.”
I merely laughed — but he seemed quite serious in all that he said.
“The measures, then,” he continued, “were good in their kind, and well executed; their defect lay in their being inapplicable to the case, and to the man. A certain set of highly ingenious resources are, with the Prefect, a sort of Procrustean bed, to which he forcibly adapts his designs. But he perpetually errs by being too deep or too shallow, for the matter in hand; and many a schoolboy is a better reasoner than he. I knew one about eight years of age, whose success at guessing in the game of ‘even and odd’ attracted universal admiration. This game is simple, and is played with marbles. One player holds in his hand a number of these toys, and demands of another whether that number is even or odd. If the guess is right, the guesser wins one; if wrong, he loses one. The boy to whom I allude won all the marbles of the school. Of course he had some principle of guessing; and this lay in mere observation and admeasurement of the astuteness of his opponents. For example, an arrant simpleton is his opponent, and, holding up his closed hand, asks, ‘are they even or odd?’ Our schoolboy replies, ‘odd,’ and loses; but upon the second trial he wins, for he then says to himself, the simpleton had them even upon the first trial, and his amount of cunning is just sufficient to make him have them odd upon the second; I will therefore guess odd’; — he guesses odd, and wins. Now, with a simpleton a degree above the first, he would have reasoned thus: ‘This fellow finds that in the first instance I guessed odd, and, in the second, he will propose to himself upon the first impulse, a simple variation from even to odd, as did the first simpleton; but then a second thought will suggest that this is too simple a variation, and finally he will decide upon putting it even as before. I will therefore guess even’ guesses even, and wins. Now this mode of reasoning in the schoolboy, whom his fellows termed “lucky,"— what, in its last analysis, is it?”
“It is merely,” I said, “an identification of the reasoner’s intellect with that of his opponent.”
“It is,” said Dupin;” and, upon inquiring of the boy by what means he effected the thorough identification in which his success consisted, I received answer as follows: ‘When I wish to find out how wise, or how stupid, or how good, or how wicked is any one, or what are his thoughts at the moment, I fashion the expression of my face, as accurately as possible, in accordance with the expression of his, and then wait to see what thoughts or sentiments arise in my mind or heart, as if to match or correspond with the expression.’ This response of the schoolboy lies at the bottom of all the spurious profundity which has been attributed to Rochefoucauld, to La Bougive, to Machiavelli, and to Campanella.”
“And the identification,” I said, “of the reasoner’s intellect with that of his opponent, depends, if I understand you aright upon the accuracy with which the opponent’s intellect is admeasured.”
“For its practical value it depends upon this,” replied Dupin; and the Prefect and his cohort fall so frequently, first, by default of this identification, and, secondly, by ill-admeasurement, or rather through non-admeasurement, of the intellect with which they are engaged. They consider only their own ideas of ingenuity; and, in searching for anything hidden, advert only to the modes in which they would have hidden it. They are right in this much — that their own ingenuity is a faithful representative of that of the mass; but when the cunning of the individual felon is diverse in character from their own, the felon foils them, of course. This always happens when it is above their own, and very usually when it is below. They have no variation of principle in their investigations; at best, when urged by some unusual emergency — by some extraordinary reward — they extend or exaggerate their old modes of practice, without touching their principles. What, for example, in this case of D — has been done to vary the principle of action? What is all this boring, and probing, and sounding, and scrutinizing with the microscope, and dividing the surface of the building into registered square inches — what is it all but an exaggeration of the application of the one principle or set of principles of search, which are based upon the one set of notions regarding human ingenuity, to which the Prefect, in the long routine of his duty, has been accustomed? Do you not see he has taken it for granted that all men proceed to conceal a letter — not exactly in a gimlet-hole bored in a chair-leg — but, at least, in some hole or corner suggested by the same tenor of thought which would urge a man to secrete a letter in a gimlet-hole bored in a chair-leg? And do you not see also, that such recherches nooks for concealment are adapted only for ordinary occasions, and would be adopted only by ordinary intellects; for, in all cases of concealment, a disposal of the article concealed — a disposal of it in this recherche manner — is, in the very first instance, presumable and presumed; and thus its discovery depends, not at all upon the acumen, but altogether upon the mere care, patience, and determination of the seekers; and where the case is of importance — or, what amounts to the same thing in the policial eyes, when the reward is of magnitude — the qualities in question have never been known to fall. You will now understand what I meant in suggesting that, had the purloined letter been hidden anywhere within the limits of the Prefect’s examination — in other words, had the principle of its concealment been comprehended within the principles of the Prefect — its discovery would have been a matter altogether beyond question. This functionary, however, has been thoroughly mystified; and the remote source of his defeat lies in the supposition that the Minister is a fool, because he has acquired renown as a poet. All fools are poets; this the Prefect feels; and he is merely guilty of a non distributio medii in thence inferring that all poets are fools.”
“But is this really the poet?” I asked. “There are two brothers, I know; and both have attained reputation in letters. The Minister I believe has written learnedly on the Differential Calculus. He is a mathematician, and no poet.”
“You are mistaken; I know him well; he is both. As poet and mathematician, he would reason well; as mere mathematician, he could not have reasoned at all, and thus would have been at the mercy of the Prefect.”
“You surprise me,” I said, “by these opinions, which have been contradicted by the voice of the world. You do not mean to set at naught the well-digested idea of centuries. The mathematical reason has long been regarded as the reason par excellence.
“‘Il y a a parier,’” replied Dupin, quoting from Chamfort, “‘que toute idee publique, toute convention recue, est une sottise, car elle a convenu au plus grand nombre.’ The mathematicians, I grant you, have done their best to promulgate the popular error to which you allude, and which is none the less an error for its promulgation as truth. With an art worthy a better cause, for example, they have insinuated the