Here are some quotes from The Sign of Four:
"My mind," he said, "rebels at stagnation. Give me problems, give me work, give me the most abstruse cryptogram or the most intricate analysis, and I am in my own proper atmosphere. I can dispense then with artificial stimulants. But I abhor the dull routine of existence. I crave for mental exaltation. That is why I have chosen my own particular profession,—or rather created it, for I am the only one in the world."
Sherlock Holmes says this to Dr. Watson at the beginning of the book. Holmes craves the excitement of cracking cases through the process he calls "deduction"—using a mass of evidence to solve a mystery. He is, in fact, the only detective in the world to use this process, and he is in a class by himself. However, when in between cases, he feels at loose ends. He takes cocaine to soothe himself at these times, and Dr. Watson finds this practice both intriguing and revolting. Watson himself does not use cocaine.
"Detection is, or ought to be, an exact science, and should be treated in the same cold and unemotional manner. You have attempted to tinge it with romanticism, which produces much the same effect as if you worked a love-story or an elopement into the fifth proposition of Euclid."
This is Holmes's pronouncement on the science of detection. He treats it as a science, and he is cold and rational in his decision-making. Watson, however, is more romantic, and Holmes criticizes this tendency in Watson. Holmes says it's like introducing a love story into the geometry developed by Euclid. Holmes is successful because he is so rational and detached.
"You really are an automaton,—a calculating-machine!" I cried. "There is something positively inhuman in you at times."
Watson says this to Holmes when Watson observes that Miss Morstan is quite attractive. Holmes replies that he did not notice her looks at all, which shocks Watson. In Watson's mind, Holmes is strange and almost inhuman. However, it is Holmes's detachment and scientific mind that make him a superlative detective, because he is not misled by emotions and is an excellent observer of facts.
"In the left-hand...
(The entire section is 570 words.)