can reasoning lead to overconfidence? -- 1/24/18

Today's selection -- from The Enigma of Reason by Hugo Mercier and Dan Sperber. France's infamous Dreyfus Affair of 1894 was the trial of a young Jewish military captain named Alfred Dreyfus for treason. It became a scandalous example of prejudice and miscarried justice in that the charges were based on falsified documents, and brought riots and divisions throughout France. An expert in criminal investigations, Alphonse Bertillon, was asked to determine if Dreyfus' handwriting matched that on a treasonous letter known thereafter as the bordereau. Though it clearly did not, he concocted an elaborate explanation of how that difference in handwriting actually proved the guilt of Dreyfus, since, he argued, Dreyfus had intentionally obfuscated his handwriting. A year later, further investigation uncovered a spy, Ferdinand Esterházy, whose handwriting did match that on the treasonous bordereau, but in the retrial, Bertillon was undeterred and the Dreyfus guilty verdict was upheld. In 1899, in another retrial, Bertillon went further in a 10-hour deposition. The more Bertillon defended his original conclusion, the more incapable he became of accepting the obvious explanation -- the handwriting on the treasonous document simply did not belong to Dreyfus. Among psychologists, that phenomenon, the use of reasoning to defend preexisting beliefs especially when one has previously defended those beliefs, is known as "belief persistence":

"In 1899, the orig­inal [guilty verdict] is quashed and a new trial is held in Rennes. Bertillon, again, is one of the expert witnesses. His task has become more difficult, as he must now prove that the bordereau is not an undisguised note left by the sloppy spy Esterházy but the carefully designed product of Dreyfus's devious mind. Bertillon is up to the task. Apotheosis of Bertillon's system, the deposition runs for more than fifty pages of dense text, plus pictures and exhibits.

Photograph of the bordereau dated Oct.
13 1894. The original disappeared in 1940

"Of that bordereau, Bertillon peruses every word, measures every letter, photographs every wrinkle. He sees patterns everywhere. When the thirteenth line of the bordereau is superimposed on the thirtieth, three letters are aligned. When the word intérêt is taken out and repeated and the two copies put end to end, they measure 12.5 millimeters, a unit size on military maps. Even more damning, a standard subdivision of this unit, 1.25 millimeters, is found every­where in the word: 'length of the t's cross: 3 [units of l.25 millimeters]; length of the acute accent: 1; width of the circumflex, one and a half, and height of the final t: 4, etc.' Coincidences? Impossible. The bordereau must be the work of a master craftsman who used several templates and a military-issue ruler to create one of the most complex forgeries of modern times.

"Such considerations can leave no place for doubt and so, after ten hours of deposition(!), Bertillon gives a forceful conclusion: 'In the set of observations and concordances that form my demonstration there is no place for doubt, and it is made strong by a certainty both theoretical and material that, with the feeling of responsibility born of such an absolute conviction, I affirm with all my soul, today as in 1894, under oath, that the bordereau is the work of the accused. I am done.'

"It is hard to tell how impressed the court is with Bertillon's arguments. In any case, the judges find Dreyfus guilty of treason once again, although with 'mitigating circumstances.' This nonsensical verdict reflects more the need to uphold the status quo than the merits (or lack thereof) of the case. Drey­fus's innocence is plain for anyone to see. Refusing to wait for yet a new trial that may never happen, Dreyfus consents to be pardoned by President Loubet on Septemher 19, 1899, at the cost of accepting the guilty verdict. He will have to wait seven more years for his final rehabilitation: being reinstated to his former rank in the army.

"Bertillon offers a fascinating study in the use of reasoning to defend preexisting beliefs. He seems to have been truly convinced by his own arguments. When three experts were tasked with evaluating his system, they found an 'incom­prehensible jumble' 'totally devoid of scientific value' whose absurdity was 'so blatant that one is hard put to explain the length of its exposition.' Yet they also concluded that the very 'naiveté with which [Bertillon] unveiled the secrets [of his system] would lead one to believe in his good faith.'

Alphonse Bertillon was not a handwriting expert,
but he invented the theory of "auto forgery"

"It would be easy to regard Bertillon as a madman -- many of his contempo­raries did. But that would overlook his otherwise successful professional career, how he rose through the ranks and devised new ways to catch criminals -- hardly what you would expect of a lunatic. And lest we feel too smug, every aspect of Bertillon's thinking has been reproduced in the labora­tory, showing how reasoning can lead everyone on the wrong track. These experiments have replicated -- on a smaller scale, fortunately -- the mental processes occurring in Bertillon's mind. Unambiguously, they point to rea­soning as the culprit.

"When Bertillon mentions the perfect comprehensiveness with which he embraces all the facts, he exhibits clear symptoms of overconfidence. According to the intellectualist approach, reasoning is supposed to make us doubt our own beliefs, especially when they rest on foundations as shaky as Bertillon's. How can reasoning lead to overconfidence instead?"



Hugo Mercier and Dan Sperber


The Enigma of Reason


Harvard University Press


Copyright 2017 Hugo Mercier and Dan Sperber


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