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Six methods of detection in Sherlock Holmes

Between Edgar Allan Poe’s invention of the detective story with The Murders in the Rue Morgue in 1841 and Sir Arthur Conan Doyle’s first Sherlock Holmes story A Study in Scarlet in 1887, chance and coincidence played a large part in crime fiction. Nevertheless, Conan Doyle resolved that his detective would solve his cases using reason. He modeled Holmes on Poe’s Dupin and made Sherlock Holmes a man of science and an innovator of forensic methods. Holmes is so much at the forefront of detection that he has authored several monographs on crime-solving techniques. In most cases the well-read Conan Doyle has Holmes use methods years before the official police forces in both Britain and America get around to them. The result was 60 stories in which logic, deduction, and science dominate the scene.

Finger Prints

Sherlock Holmes was quick to realize the value of fingerprint evidence. The first case in which fingerprints are mentioned is The Sign of Four, published in 1890, and he’s still using them 36 years later in the 55th story, The Three Gables (1926). Scotland Yard did not begin to use fingerprints until 1901.

It is interesting to note that Conan Doyle chose to have Holmes use fingerprints but not bertillonage (also called anthropometry), the system of identification by measuring twelve characteristics of the body. That system was originated by Alphonse Bertillon in Paris. The two methods competed for forensic ascendancy for many years. The astute Conan Doyle picked the eventual winner.

Typewritten Documents

Sherlock Holmes
Image Credit: Sherlock Holmes in “The Red-Headed League”, which appeared in The Strand Magazine in August, 1891; Public Domain via Wikimedia Commons.

As the author of a monograph entitled “The Typewriter and its Relation to Crime,” Holmes was of course an innovator in the analysis of typewritten documents. In the one case involving a typewriter, A Case of Identity (1891), only Holmes realized the importance of the fact that all the letters received by Mary Sutherland from Hosmer Angel were typewritten — even his name is typed and no signature is applied. This observation leads Holmes to the culprit. By obtaining a typewritten note from his suspect, Holmes brilliantly analyses the idiosyncrasies of the man’s typewriter. In the United States, the Federal Bureau of Investigation (FBI) started a Document Section soon after its crime lab opened in 1932. Holmes’s work preceded this by forty years.


Conan Doyle, a true believer in handwriting analysis, exaggerates Holmes’s abilities to interpret documents. Holmes is able to tell gender, make deductions about the character of the writer, and even compare two samples of writing and deduce whether the persons are related. This is another area where Holmes has written a monograph (on the dating of documents). Handwritten documents figure in nine stories. In The Reigate Squires, Holmes observes that two related people wrote the incriminating note jointly. This allows him to quickly deduce that the Cunninghams, father and son, are the guilty parties. In The Norwood Builder, Holmes can tell that Jonas Oldacre has written his will while riding on a train. Reasoning that no one would write such an important document on a train, Holmes is persuaded that the will is fraudulent. So immediately at the beginning of the case he is hot on the trail of the culprit.


Holmes also uses footprint analysis to identify culprits throughout his fictional career, from the very first story to the 57th story (The Lion’s Mane published in 1926). Fully 29 of the 60 stories include footprint evidence. The Boscombe Valley Mystery is solved almost entirely by footprint analysis. Holmes analyses footprints on quite a variety of surfaces: clay soil, snow, carpet, dust, mud, blood, ashes, and even a curtain. Yet another one of Sherlock Holmes’s monographs is on the topic (“The tracing of footsteps, with some remarks upon the uses of Plaster of Paris as a preserver of impresses”).


Sherlock Holmes solves a variety of ciphers. In The “Gloria Scott” he deduces that in the message that frightens Old Trevor every third word is to be read. A similar system was used in the American Civil War. It was also how young listeners of the Captain Midnight radio show in the 1940s used their decoder rings to get information about upcoming programs. In The Valley of Fear Holmes has a man planted inside Professor Moriarty’s organization. When he receives an encoded message Holmes must first realize that the cipher uses a book. After deducing which book, he is able to retrieve the message.

sherlock holmes
Image Credit: Sherlock Holmes in “The Man with the Twisted Lip”, which appeared in The Strand Magazine in December, 1891; Public Domain, via Wikimedia Commons.

This is exactly how Benedict Arnold sent information to the British about General George Washington’s troop movements. Holmes’s most successful use of cryptology occurs in The Dancing Men. His analysis of the stick figure men left as messages is done by frequency analysis, starting with “e” as the most common letter. Conan Doyle is again following Poe who earlier used the same idea in The Gold Bug (1843). Holmes’s monograph on cryptology analyses 160 separate ciphers.


Conan Doyle provides us with an interesting array of dog stories and analyses. The most famous line in all the sixty stories, spoken by Inspector Gregory in Silver Blaze, is “The dog did nothing in the night-time.” When Holmes directs Gregory’s attention to “the curious incident of the dog in the night-time,” Gregory is puzzled by this enigmatic clue. Only Holmes seems to realize that the dog should have done something. Why did the dog make no noise when the horse, Silver Blaze, was led out of the stable in the dead of night? Inspector Gregory may be slow to catch on, but Sherlock Holmes is immediately suspicious of the horse’s trainer, John Straker.

In Shoscombe Old Place we find exactly the opposite behavior by a dog. Lady Beatrice Falder’s dog snarled when he should not have. This time the dog doing something was the key to the solution. When Holmes took the dog near his mistress’s carriage, the dog knew that someone was impersonating his mistress. In two other cases Holmes employs dogs to follow the movements of people. In The Sign of Four, Toby initially fails to follow the odor of creosote to find Tonga, the pygmy from the Andaman Islands. In The Missing Three Quarter the dog Pompey successfully tracks Godfrey Staunton by the smell of aniseed. And of course, Holmes mentions yet another monograph on the use of dogs in detective work.

Featured Image Credit: ‘Basil Rathbone, Nigel Bruce; Sherlock Holmes’, Image by skeeze, CC0 Public Domain, via pixabay.

Recent Comments

  1. Brett Sidaway

    Great blog. I love the Sherlock Holmes stories ( as well as many of the films, TV series and ‘reboots’.) However, I think James may be a bit wide-eyed in believing the stories are a triumph of “logic, deduction, and science” – these are certainly the terms in which SH would like to see his methods triumph but any close reading of many of the stories reveal often flawed or even partial solutions – and often as much a reliance on chance, luck and fate as other narratives from the era. But I will go back to the classic stories once again with a renewed interest after this blog.

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  4. Pratyusha

    Nothing about the adventure of the crooked man….

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  6. tali

    OBSERVATION was Holmes’ #1 method. From there he then employed logic, reason, and forensic science. I am reading a giant anthology of Holmes’ adventures at the moment, so I am up-to-date. Holmes didn’t just see; he observed. He didn’t hear; he listened. I have found minor flaws in the stories, but they were few and far between. What is mysterious is that Sidney Paget, who illustrated the adventures, nailed the person of actor Basil Rathbone to the ‘T” in his sketches. Rathbone was born in 1892, far before these sketches were drawn and publicized in The Strand Magazine in England. Now, solve that one :)

  7. Lee Knights

    I watched an episode of a telly programme on the latest forensic techniques used in crime solving. This detailed the first case when mud on a shoe (aquatic evidence) was used to identify perpetrators. Wow. Conan Doyle and Sherlock Holmes way ahead of their time when the game was afoot.

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