Sherlock Holmes

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Sherlock Holmes is a famous, brilliant detective of the late 19th century, created by British author and physician Arthur Conan Doyle. Sherlock Holmes is described as a "consulting detective" who specialized in solving unusual cases using his extraordinary powers of observation and "deduction" (see below). Conan Doyle loosely based Holmes on the 19th century forensic detective, a teacher at medical school, Joseph Bell.

In many of the stories he is assisted by his companion, the practical Dr. John H. Watson, with whom Holmes shared rooms for some time, before Watson's marriage. Watson is portrayed as Holmes' friend and chronicler, i.e., Holmes' stories are actually told as reports, by Watson, of Holmes' solutions to actual crimes. He also has a brother Mycroft Holmes who appears in at least three stories: "The Adventure of the Greek Interpreter," "The Adventure of the Final Problem," and "The Adventure of the Bruce Partington Plans."

In the very first Holmes story, "A Study in Scarlet," something of Holmes' background is given. He is presented as an independent student of chemistry with a variety of very curious side-interests--which turn out all to be single-mindedly bent toward making Holmes superior at solving crimes. In another early Holmes story, "The Adventure of the 'Gloria Scott'," we get more background on what caused Holmes to become a detective: a college friend's father complimented him very highly on his deductive skills.

Holmes' arch-enemy, and popularly-supposed nemesis was Professor James Moriarty, who pushed Holmes over the Reichenbach Falls. Conan Doyle intended the story where Holmes is pushed over the cliff to be the last that he wrote about Holmes; however the mass of mailings he received demanding that he bring Holmes back convinced him to continue. The next Holmes story had Conan Doyle explaining that Holmes did not in fact die, but managed to grab hold of some vegetation on the side of the cliff; this explanation originated the term "cliffhanger." Notably, Moriarty does not appear directly in the stories; Watson never encounters Moriarty, and so the encounters between Holmes and his nemesis are described by Holmes.

Modern readers of the Holmes stories are apt to be surprised that he is an avid user of cocaine, though Watson describes this as Holmes' "only vice." Watson might not have considered vices Holmes' habit of smoking (usually a pipe) like a chimney, or his tendency to bend the truth and break the law when it suits his purposes (in Victorian England these were probably not considered vices as long as they were done by a gentleman for noble purposes). Holmes is not at all a stuffy straight-laced gentleman; in fact, he describes himself and his habits as "Bohemian."

Holmesian (or Sherlockian) deduction

"From a drop of water"--Holmes wrote in an essay described in "A Study in Scarlet"--"a logician could infer the possibility of an Atlantic or a Niagara without having seen or heard of one or the other." Holmes stories often begin with a bravura display of Holmes' talent for "deduction." It is of some interest to logicians and those interested in logic to try to analyze just what Holmes is doing when he performs his deduction. Holmesian (that's the British adjective; Americans say "Sherlockian") deduction appears to consist primarily of drawing inferences based on either straightforward practical principles--which are the result of careful inductive study, such as Holmes' study of different kind of cigar ashes--or inference to the best explanation. In many cases, the inference can be modelled either way.

Holmes' straightforward practical principles are generally of the form, "If p, then q," where 'p' is observed evidence and 'q' is what the evidence indicates. But there are also, as one may observe in the following example, often some intermediate principles. In "A Scandal in Bohemia," Holmes deduces that Watson had gotten very wet lately and that he had "a most clumsy and careless servant girl." When Watson, in amazement, asks how Holmes knows this, Holmes answers:

It is simplicity 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.

In this case, we might say Holmes employed several connected principles such as these:

  1. If leather on the side of a shoe is scored by several parallel cuts, they were caused by someone who scraped around the edges of the sole in order to remove crusted mud from it.
  2. If a nineteenth-century London doctor's shoes are scraped to remove crusted mud, the person who so scrapes them is the doctor's servant girl.
  3. If someone cuts a shoe while scraping it to remove encrusted mud, that person is clumsy and careless.
  4. If someone's shoes had encrusted mud on them, that person has been very wet lately and has been out in vile weather.

By applying such principles in an obvious way (using repeated applications of modus ponens), Holmes is able to infer from

p: The sides of Watson's shoes are scored by several parallel cuts.


q1: Watson's servant girl is clumsy and careless.


q2: Watson has been very wet lately and has been out in vile weather.

In other instances of Holmesian deduction, it is more difficult to model his inference as deduction using general principles, and logicians and scientists will readily recognize the method used, instead, as an inductive one--in particular, argument to the best explanation, or, in Charles S. Peirce's terminology, abduction. (That Holmes should have called this deduction is entirely plausible, however, because, in several stories, Holmes is said not to have known anything at all of philosophy.)

The instances in which Holmes uses abduction tend to be those where he has amassed a large body of evidence, produced a number of possible explanations of that evidence, and then proceeds to find one explanation that is clearly the best at explaining the evidence. For example, in "The Sign of Four," a certain man is found dead in his room, with a ghastly smile on his face, and with no immediately visible cause of death. From a whole body of background information as well as evidence gathered at and around the scene of the crime, Holmes is able to infer that the murderer is--not the various people that Scotland Yard has in custody (each of them being an alternative explanation)--but rather...well, we don't want to give away the story, but you get the idea. As Holmes says in the story, "How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth?"

In the latter example, in fact, Holmes' solution of the crime depends both on a series of applications of general principles and argument to the best explanation.

Holmes' success at his brand of deduction, therefore, is due to his mastery of both a huge body of particular knowledge of things like footprints, cigar ashes, and poisons, which he uses to make relatively simple deductive inferences, and the fine art of ordering and weighing different competing explanations of a body of evidence. Holmes is also particularly good at gathering evidence by observation, as well locating and tracking the movements of criminals through the streets of London and environs (in order to produce more evidence)--skills that have little to do with deduction per se, but everything to do with providing the premises for particular Holmesian deductions.

The Canon

Conan Doyle wrote four novels and fifty-six short stories about Sherlock Holmes. (Or, as some would have it: Dr. John H. Watson wrote four long accounts and fifty-two short accounts of Holmes's cases, while Holmes wrote two of his own and a third, unnamed person -- possibly Conan Doyle -- wrote two more.) The stories appeared in magazine serialization, notably in The Strand, over a period of forty years.


Short stories (organized by collection):

A Scandal in Bohemia
The Red-Headed League
A Case of Identity
The Boscombe Valley Mystery
The Five Orange Pips
The Man with the Twisted Lip
The Adventure of the Blue Carbuncle
The Adventure of the Speckled Band
The Adventure of the Engineer's Thumb
The Adventure of the Noble Bachelor
The Adventure of the Beryl Coronet
The Adventure of the Copper Beeches
The Adventure of Silver Blaze
The Adventure of the Cardboard Box
The Adventure of the Yellow Face
The Adventure of the Stockbroker's Clerk
The Adventure of the "Gloria Scott" (Holmes's first case, described to Watson)
The Adventure of the Musgrave Ritual (another early case, told by Holmes to Watson)
The Adventure of the Reigate Squire
The Adventure of the Crooked Man
The Adventure of the Resident Patient
The Adventure of the Greek Interpreter
The Adventure of the Naval Treaty
The Adventure of the Final Problem (Watson reports the death of Holmes)
Note: Frequently, "The Adventure of ..." is dropped from some story titles in current-day anthologies. However, in their original appearance in The Strand, this is how the titles were given.)
The Adventure of the Empty House (the return of Holmes)
The Adventure of the Norwood Builder
The Adventure of the Dancing Men
The Adventure of the Solitary Cyclist
The Adventure of the Priory School
The Adventure of Black Peter
The Adventure of Charles Augustus Milverton
The Adventure of the Six Napoleons
The Adventure of the Three Students
The Adventure of the Golden Pince-Nez
The Adventure of the Missing Three-Quarter
The Adventure of the Abbey Grange
The Adventure of the Second Stain
The Adventure of the Illustrious Client
The Adventure of the Blanched Soldier
The Adventure of the Mazarin Stone (told in third-person)
The Adventure of the Three Gables
The Adventure of the Sussex Vampire
The Adventure of the Three Garridebs
The Problem of Thor Bridge
The Adventure of the Creeping Man
The Adventure of the Lion's Mane (narrated by Holmes)
The Adventure of the Veiled Lodger
The Adventure of Shoscombe Old Place
The Adventure of the Retired Colourman
The Singular Experience of Mr. John Scott Eccles
The Tiger of San Pedro
(the above two stories are usually combined in the anthologies as "The Adventure of Wisteria Lodge", but their original appearance bore no such title)
The Adventure of the Cardboard Box
The Adventure of the Red Circle
The Adventure of the Bruce-Partington Plans (Mycroft appears)
The Adventure of the Dying Detective
The Disappearance of Lady Francis Carfax
The Adventure of the Devil's Foot
His Last Bow (Holmes's war-time service; told in third-person)

"The Hiatus"

Holmes fans refer to the period from 1891 to 1894 -- the time between Holmes's disappearance and presumed death in "The Final Problem" and his reappearance in "The Adventure of the Empty House" -- as "the Hiatus". It is notable, though, that one later story ("The Adventure of Wisteria Lodge") is described as taking place in 1892.

For Conan Doyle, writing the stories, the period is ten years. Conan Doyle, wanting to devote more time to his historical novels, killed off Holmes in "The Final Problem", which appeared in print in 1893. After resisting public pressure for eight years, Conan Doyle wrote "The Hound of the Baskervilles", which appeared in 1901. The public, while pleased with the story, were not satisfied with a posthumous Holmes, and so Conan Doyle resuscitated Holmes two years later. Many have speculated on Conan Doyle's motives for bringing Holmes back to life, notably writer-director Nicholas Meyer, who wrote an essay on the subject in the 1970s, but the actual motives are not known. For whatever reason, Conan Doyle continued to write Holmes stories for a quarter-century more (or, as some would have it, acted as Watson's agent for publication of Watson's memoirs for that period).

Text of some of the stories is available at 221B Baker Street

Perhaps see also Scotland Yard.