“Beyond the obvious facts that he has at some time done manual labour, that he takes snuff, that he is a Freemason, that he has been in China, and that he has done a considerable amount of writing lately, I can deduce nothing else.”

― Arthur Conan Doyle, The Red Headed League

The great detective was wrong. Or, to be fair, Arthur Conan Doyle was wrong.

Sherlock Holmes is known for a few things: his deerstalker cap, his various addictions, his saying “Elementary, my dear Watson” (which actually never appeared in this form in the Conan Doyle stories), and his superhuman deductive skills.

Scratch that.

Sherlock Holmes did not practice deduction.

A deduction is a logical process by which one reaches a conclusion which is absolutely certain in the face of a set of facts. It starts from the general and moves to the particular.

Here is a classic deduction: