====== Sherlock-Holmes Fallacy ======

An alternative name for the [[logic:induction:eliminative_induction|fallacy of eliminative induction]].

This name refers to [[wp>Arthur Conan Doyle|Arthur Conan Doyle]]’s literary detective [[wp>Sherlock Holmes|Sherlock Holmes]], who used the following description of his truth-finding strategy:

> <u questionable "Sherlock-Holmes fallacy">“Once you have ruled out the impossible, then whatever remains, no matter how improbable, must be the truth.”</u>((This idea is paraphrased with slight variations in multiple novels, notably in: “[[https://www.arthur-conan-doyle.com/index.php/The_Fate_of_the_Evangeline|The Fate of the Evangeline]]” (1885), multiple times in “[[wp>The Sign of the Four|The Sign of the Four]]” (1890), and finally in “[[wp>The Adventure of the Beryl Coronet|The Adventure of the Beryl Coronet]]” (1892).))

This approach actually describes an [[glossary:abduction|abductive]] method which – except in certain //very specific// situations – at best leads to a //probably// correct result, but never a //certain// one.

The underlying //fallacy// here is a confusion of the [[glossary:abduction|abductive]] method (specifically a method called “eliminative induction”) with a [[glossary:deduction|deduction]], and as a consequence, ignoring the level of //uncertainty// that this method entails.

The way that Sherlock-Homes’ method is stated, it can be paraphrased as follows:

> Either ''A'', or ''B'', etc. … or ''N''.
> ''A'' is //false//.
> ''B'' is //false//.
> … and so on.
> <span conclusio>Therefore: <u questionable>''N'' must be //true//</u>.</span>

This method, which //can be// a valid approach under //certain// circumstances, particularly within //formal systems// such as mathematics. However, comes up against its limits in more complex situations (such as in [[wp>Forensic science|forensics]]), where the number of //possible// explanations is practically //unlimited// and no option can ever be ruled out with //complete certainty//. 

And indeed, the hero of the aforementioned novels uses almost exclusively [[glossary:abduction|abductive]] reasoning to solve the cases, a form of reasoning that does not fulfil the formal requirements of such a rigid methodology.

However, as a //fictional// character in a novel, Sherlock Holmes has the advantage that his author can ensure that his findings always turn out to be //true//.

For more information, see: <b maniculus "See also:">[[logic:induction:eliminative_induction|Fallacy of eliminative induction]]</b>.

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