His ignorance was as remarkable as his knowledge. Of contemporary literature, philosophy and politics he appeared to know next to nothing. Upon my quoting Thomas Carlyle, he inquired in the naivest way who he might be and what he had done. My surprise reached a climax, however, when I found incidentally that he was ignorant of the Copernican Theory and of the composition of the Solar System. That any civilized human being in this nineteenth century should not be aware that the earth travelled round the sun appeared to be to me such an extraordinary fact that I could hardly realize it.
“You appear to be astonished,” he said, smiling at my expression of surprise. “Now that I do know it I shall do my best to forget it.”
“To forget it!”
“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, so that the knowledge which might be useful to him gets crowded out, or at best is jumbled up with a lot of other things so that he has a difficulty in laying his hands upon it. Now the skilful 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, but of these he has a large assortment, and all in the most perfect order. It is a mistake to think that that little room has elastic walls and can distend to any extent. Depend upon it there comes a time when for every addition of knowledge you forget something that you knew before. It is of the highest importance, therefore, not to have useless facts elbowing out the useful ones.”
“But the Solar System!” I protested.
“What the deuce is it to me?” he interrupted impatiently; “you say that we go round the sun. If we went round the moon it would not make a pennyworth of difference to me or to my work.”
I was on the point of asking him what that work might be, but something in his manner showed me that the question would be an unwelcome one. I pondered over our short conversation, however, and endeavoured to draw my deductions from it. He said that he would acquire no knowledge which did not bear upon his object. Therefore all the knowledge which he possessed was such as would be useful to him. I enumerated in my own mind all the various points upon which he had shown me that he was exceptionally well-informed. I even took a pencil and jotted them down. I could not help smiling at the document when I had completed it. It ran in this way—
SHERLOCK HOLMES—his limits.
1. Knowledge of Literature.—Nil. 2. Philosophy.—Nil. 3. Astronomy.—Nil. 4. Politics.—Feeble. 5. Botany.—Variable. Well up in belladonna, opium, and poisons generally. Knows nothing of practical gardening. 6. Geology.—Practical, but limited. Tells at a glance different soils from each other. After walks has shown me splashes upon his trousers, and told me by their colour and consistence in what part of London he had received them. 7. Chemistry.—Profound. 8. Anatomy.—Accurate, but unsystematic. 9. Sensational Literature.—Immense. He appears to know every detail of every horror perpetrated in the century. 10. Plays the violin well. 11. Is an expert singlestick player, boxer, and swordsman. 12. Has a good practical knowledge of British law.
When I had got so far in my list I threw it into the fire in despair. “If I can only find what the fellow is driving at by reconciling all these accomplishments, and discovering a calling which needs them all,” I said to myself, “I may as well give up the attempt at once.”
— Sir Arthur Conan Doyle, A Study in Scarlet, Chapter II: The Science of Deduction.