In Part 1, Chapter 2, Sherlock Holmes uses a simile to describe the way he views the mind, comparing it to an attic. Watson is shocked to learn that someone as brilliant as Holmes is supposedly ignorant of the Copernican model of the solar system (the idea that planets revolve around the sun). Holmes claims that he has simply never thought about the position of the sun in the solar system because it isn’t relevant to his goals:
“You see,” he explained, “I consider that a man’s brain originally is like a little empty attic, and you have to stock it with such furniture as you choose. A fool takes in all the lumber of every sort that he comes across […] Now the skillful workman is very careful indeed as to what he takes into his brain-attic. He will have nothing but the tools which may help him in doing his work […] It is a mistake to think that the little room has elastic walls and can distend to any extent.”
While the truth of Holmes’s simile for the human mind is certainly debatable, it reveals a lot of important information about his character. Much of Holmes’s skill as a detective comes from his extraordinary focus and attention to detail. He assures Watson that his ability to deduce people’s occupations within moments of meeting them isn’t due to some particular, inherent genius of his, but rather to the way he has trained himself to pay close attention to observable clues, like what someone is wearing, their appearance, their posture, and their body language. In his article “The Book of Life,” he encourages readers to train these observational abilities in themselves, allowing them to make their own deductions about the people around them.
This simile also reveals how much Holmes values his own mind. Although it may be unfair to call someone who has gathered a lot of knowledge in many different fields “a fool,” this opinion nonetheless shows that Holmes values his intellectual abilities enough to make sure his brain isn’t crowded with useless information, distracting him from pursuing his true passions and interests, like chemistry and detective work.