Observation is Knowledge
The old saying is that knowledge is power. What Sherlock Holmes teaches is that the power of observation creates knowledge that leads to more power. Every Holmes story is a recurring motif of the knowledge that can be gained about a person or situation by doing nothing more than actually looking rather than merely seeing.
All that Glitters is Too Good to be True
Many characters in the stories in this Holmes collection learn that the following proverb is true: if it seems too good to be true, it’s probably not worth the effort. Jabez Wilson falls for a wildly improbable opportunity to make an incredible sum of money on the basis of nothing more than having red hair and copying sections of the encyclopedia. Violet Hunter is appropriately worried about taking a job that pays beyond all reason for the sacrifice of her luxurious hair an hour a day sitting with her back to the window. The characters who are tempted by the glitter of a golden opportunity are taught a lesson on avoiding things that are probably way too good to be true.
Appearances are Deceiving
The nature of appearance and identity is a common theme running throughout this collection. “A Case of Identity” actually involves a plot in which the suspect tries to deceive his stepdaughter by disguising himself. The titular, filthy street beggar in rags that spouts Shakespeare in “The Man with the Twisted Lip” takes off his disguise, cleans himself up and goes back home to his nice house with his pretty young wife none the wiser. Meanwhile, in the ex-con arrested by the police for stealing in “The Blue Carbuncle” turns not to be the criminal after all, despite appearances to the contrary.
Mercy and Judgment
A motif that pops up throughout the entire Holmes canon is that of getting a second chance after making mistakes. The suspected thief of the carbuncle in “The Blue Carbuncle” is targeted by the police because of a previous criminal record, but proves to be an example of prisoner rehabilitation. In the same story, Holmes unilaterally allows the real thief to go free after sensing his genuine remorse and the probability that he has been scared straight for life. Holmes plays the same role of judge and jury in releasing John Turner after solving the “Bascombe Valley Mystery.” Mercy is shown toward the guilty who show repentance and conscience, whereas those who reveal as irredeemable sort of evil tend to get their just desserts, like the man who uses a trained snake as a murder weapon and the father who attempts to turn the Copper Beeches into a prison for his daughter.
Reputation and Its Maintenance
Although some of the more sensationalist of Holmes' cases involve grave dangers to life (e.g., "The Adventure of the Speckled Band") or murders already committed, many are quite dramatic without any sort of physical violence. The first story in the collection, "A Scandal in Bohemia," makes clear the dramatic tension that animates those stories: personages of high rank and repute fearing the compromise of their positions because of some foible of theirs and/or plot by others.
Fear versus Knowledge
One important reason that Watson, rather than Holmes, is the narrator of Holmes' adventures is that the difference between Watson's and Holmes' knowledge of the cases and particular situations allows for the building of the great suspense and then the highly satisfying explanations by Holmes. As a former officer with combat experience, Watson is also especially attuned to the psychology of stress, which allows for such scenes as his waiting in ambush along with Holmes for the bank robbers in "The Red-headed League."
Class Difference
The different adventures in the collection, while touching upon many different personalities, places, and types of problems, nevertheless take place in a single and very coherently understood milieu: British society (mostly in London) at the end of the 19th century. As such, the defining importance of social class at the time ends up functioning as a thread that links together many stories that are otherwise completely disparate; even Holmes himself notes these connections, such as when he tells Lord Saint-Simon that he has worked a case for a king before.
