The Sign of the Four (Sherlock Holmes, #2)

by Arthur Conan Doyle

He possesses two out of the three qualities necessary for the ideal detective. He has the power of observation and that of deduction. He is only wanting in knowledge; and that may come in time.

Eliminate all other factors, and the one which remains must be the truth."

"How often have I said to you that when you have eliminated the impossible whatever remains, HOWEVER IMPROBABLE, must be the truth?