In Part 1, Chapter 2, Doyle uses situational irony to underscore Sherlock Holmes’s uncanny abilities of deduction. Although Holmes is immediately able to guess that Watson was an army doctor upon meeting him, Watson is at a loss for what Holmes might do for a living, even after he has been living with him for several weeks. Watson becomes increasingly fascinated by the mystery surrounding his new roommate. When Holmes tells him that “he would not acquire knowledge” that isn’t directly relevant to his particular occupation, Watson writes down a list of everything Holmes possesses knowledge about in an attempt to solve the mystery:
1. Knowledge of Literature: Nil
2. Knowledge of Philosophy: Nil
3. Knowledge of Astronomy: Nil
4. Knowledge of Politics: Feeble
5. Knowledge of Botany: Well up on […] poisons […]
6. Knowledge of Geology: Practical, but limited […] has shown me splashes [of dirt] upon his trousers, and told me by their colour […] in what part of London he received them
7. Knowledge of Chemistry: Profound
8. Knowledge of Anatomy: Accurate, but unsystematic
9. Knowledge of Sensational Literature: Immense. He appears to know every detail of every horror perpetrated in the century
10. Plays the violin well
11. Is in expert singlestick player […]
12. Has a good practical knowledge of British law
However, even with all the evidence laid out before him in this way, Watson is unable to piece together that Holmes is a detective—even when this conclusion is staring him right in the face. Holmes, on the other hand, takes a similar stock of all the evidence available to him about Watson and is immediately able to piece together his former occupation, as he explains in Part 1, Chapter 2:
“I knew you came from Afghanistan. From long habit the train of thoughts ran so swiftly through my mind, that I arrived at the conclusion without being conscious of intermediate steps. There were such steps, however. The train of reasoning ran, ‘Here is a gentleman of a medical type, but with the air of a military man. Clearly an army doctor, then. He has just come from the tropics, for his face is dark […] He has undergone hardship and sickness, as his haggard face says clearly. His left arm has been injured. He holds it in a stiff and unnatural manner.”
Watson’s inability to deduce Holmes’s occupation as a detective from the available evidence underscores Holmes’s own powerful skills of deduction. As Holmes explains in the above passage, he is able to arrive at such conclusions instantly, without effort, while Watson laboriously writes out a list and remains stumped.
This section of the novel also highlights an irony within Holmes’s own personality: that although he is able to solve any mystery with ease, the people around him are unable to solve the mystery of him. It isn’t just Watson who is stumped—at the beginning of the novel, their mutual friend Stamford tells Watson that Holmes is eccentric and something of a mystery, and that he has no idea what Holmes might be studying at the chemical laboratory because “his studies are very desultory and eccentric.” Since Holmes himself is extremely reticent about his studies and his detective work, it is no surprise that other people see him as a mystery. Ironically, Holmes knows a lot about other people just from looking at them, but he makes sure that other people know very little about him by keeping his personal information secret.
