When considering the character of Sherlock Holmes, almost as ubiquitous as deductive reasoning and pipe smoking is the presence of the violin, an instrument of which Watson claims Holmes is a master.
To this reader, the most fascinating purpose served by giving Holmes an instrument, especially a hand-held one that is easily produced whenever desired, is that it allowed Conan Doyle to show a side of Holmes not seen during cases.
Very early in the canon, Watson begins to understand Holmes as both a logician and a musician, and throughout the stories, both sides of the detective continue to coexist. The scientific side is at the fore during interactions with criminals and law enforcement, as well as the gathering of clues and reasoning through their implications.
To see the detective as a logical machine, however, is to limit him more than his creator did. Almost from the beginning, Watson also chronicles another side of Holmes, a dreamy, excitable, passionate side that is awakened by music and also produces it. To fail to recall Watson’s vivid descriptions of this state is to lose a large and valuable part of Holmes’s personality.
Sherlock Holmes is a far from one-dimensional character, and his violin is a symbol of the fact that the scientist, however cold he seems at times, also possesses a passionate nature.