"I have a trade of my own. I suppose I am the only one in the world. I’m a consulting detective, if you can understand what that is."

"Our minds are like a blank sheet of paper, to be filled in with facts."

"Depend upon it, there is nothing so unnatural as the commonplace."

"Never trust to general impressions, my dear Watson, but concentrate yourself upon details."

"I have no doubt that there are other planets inhabited by intelligent beings."