Editing Sherlock Holmes (section)

===Holmesian deduction===
[[File:Abbe-03.jpg|thumb|upright|alt=Colour illustration of Holmes bending over a dead man in front of a fireplace|Sidney Paget illustration of Holmes examining a corpse for "[[The Adventure of the Abbey Grange]]"]]

Holmes observes the dress and attitude of his clients and suspects, noting skin marks (such as tattoos), contamination (such as ink stains or clay on boots), emotional state, and physical condition in order to deduce their origins and recent history. The style and state of wear of a person's clothes and personal items are also commonly relied on; in the stories, Holmes is seen applying his method to items such as walking sticks,<ref>Klinger III, pp. 387-392—''The Hound of the Baskervilles''</ref> pipes,<ref>Klinger I, pp. 450-453—"The Yellow Face"</ref> and hats.<ref>Klinger I, pp. 201-203—"The Adventure of the Blue Carbuncle"</ref> For example, in "A Scandal in Bohemia", Holmes infers that Watson had got wet lately and had "a most clumsy and careless servant girl". When Watson asks how Holmes knows this, the detective answers:

{{Blockquote|It is simplicity itself&nbsp;... my eyes tell me that on the inside of your left shoe, just where the firelight strikes it, the leather is scored by six almost parallel cuts. Obviously they have been caused by someone who has very carelessly scraped round the edges of the sole in order to remove crusted mud from it. Hence, you see, my double deduction that you had been out in vile weather, and that you had a particularly malignant boot-slitting specimen of the London slavey.<ref>Klinger I, p. 9—"A Scandal in Bohemia"</ref>}}

In the first Holmes story, ''A Study in Scarlet'', Dr. Watson compares Holmes to [[C. Auguste Dupin]], Edgar Allan Poe's fictional detective, who employed a similar methodology. Alluding to an episode in "[[The Murders in the Rue Morgue]]", where Dupin determines what his friend is thinking despite their having walked together in silence for a quarter of an hour, Holmes remarks: "That trick of his breaking in on his friend's thoughts with an apropos remark&nbsp;... is really very showy and superficial."<ref>Klinger III, p. 42—''A Study in Scarlet''</ref> Nevertheless, Holmes later performs the same 'trick' on Watson in "[[The Adventure of the Cardboard Box|The Cardboard Box]]"<ref>Klinger I, pp. 423-426—"The Cardboard Box"</ref> and "[[The Adventure of the Dancing Men]]".<ref>Klinger II, pp. 864-865—"The Adventure of the Dancing Men"</ref>

Though the stories always refer to Holmes's intellectual detection method as "[[Deductive reasoning|deduction]]", Holmes primarily relies on [[abductive reasoning|abduction]]: [[Inference|inferring]] an explanation for observed details.<ref name="Bird">{{Cite book |url=https://books.google.com/books?id=yMDWLq2FdrIC|title=Oxford studies in epistemology|editor1=Tamar Szabo Gendler |editor-first2=John |editor-last2=Hawthorne |first=Alexander |last=Bird |chapter=Abductive Knowledge and Holmesian Inference |page=11 |isbn=978-0-19-928590-7 |date=27 June 2006|publisher=OUP Oxford }}</ref><ref>{{harvnb|Sebeok|Umiker-Sebeok|1984|pp=19–28, esp. p. 22}}</ref><ref>{{cite book |title=Fact and feeling: Baconian science and the nineteenth-century literary imagination |page=214 |first=Jonathan |last=Smith |year=1994 |publisher=Univ of Wisconsin Press |url=https://books.google.com/books?id=hFn1Zx_desIC |isbn=978-0-299-14354-1 |access-date=29 September 2020 |archive-date=19 February 2024 |archive-url=https://web.archive.org/web/20240219042335/https://books.google.com/books?id=hFn1Zx_desIC |url-status=live }}</ref> "From a drop of water," he writes, "a logician could infer the possibility of an [[Atlantic Ocean|Atlantic]] or a [[Niagara Falls|Niagara]] without having seen or heard of one or the other."<ref>Klinger III, p. 40—''A Study in Scarlet''</ref> However, Holmes does employ deductive reasoning as well. The detective's guiding principle, as he says in ''The Sign of Four'', is: "When you have eliminated the impossible, whatever remains, however improbable, must be the truth."<ref>{{cite web |last=Bennett|first=Bo|title=Pseudo-Logical Fallacies |url=https://www.logicallyfallacious.com/logicalfallacies/Pseudo-Logical-Fallacies |website=Logicallyfallacious.com |publisher=Logically Fallacious |access-date=31 July 2020 |archive-url=https://archive.today/20200731172256/https://www.logicallyfallacious.com/logicalfallacies/Pseudo-Logical-Fallacies |archive-date=31 July 2020 |url-status=live}}</ref>

Holmes follows [[Sir Isaac Newton]]'s rule of ''"hypotheses non fingo"'', for instance commenting in "[[A Scandal in Bohemia]]": "It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts." 

Despite Holmes's remarkable reasoning abilities, Conan Doyle still paints him as fallible in this regard (this being a central theme of "[[The Adventure of the Yellow Face|The Yellow Face]]").<ref>Klinger I, pp. 449-471—"The Yellow Face"</ref>