Wikipedia 10K Redux by Reagle from Starling archive. Bugs abound!!!
Sherlock Holmes is depicted as both a supremely logical thinker and a supernaturally astute observer. What hidden advantage did he hold over his peers? Consider: Holmes observed the world around him in a manner which took into account the most minor details. Those around him seldom detected the same "clues" and when they did, the evidence in front of their eyes was empty to them. Conan Doyle may or may not have consciously given Holmes an unfair leg up over his compatriots - but regardless of intent, that advantage existed. It is unlikely that persons who have not undertaken one form or another of professional investigation will detect how the "Holmes" world view differed from others. It is equally unlikely that it would reveal itself to professional investigators (be they involved in science, law enforcement or private investigation) who have not also made a targeted study of the science of logic and its associated processes. Logic is commonly seen as a study involving datasets, relationships between them, belonging and not-belonging. This view will serve as well as any other to illustrate the synergy which exists between the three most basic elements of successful investigative technique: A) Perception B) Knowledge Base C) Logic One must needs be able to see the world in front of one's nose in order to succeed at an investigative endeavor. And by that, it is meant only to perceive - not to perceive and imbue with meaning and nuance, but merely perceive - to be accurate and complete in perception, to record accurately what is perceived, and to add or subtract nothing. The oft-overlooked fact is that things perceived do not have meaning inherent in them. That which is perceived must be compared to a knowledge base to determine what relationships exist between elements observed and other known data. The relationships that are available serve to establish what meaning or sets of meanings may be attributed to observed items, facts or circumstances. Take this example: A suspect leaves his house at 8:00 am and arrives in a neighboring town at 10:00 AM. What are we to make of this? In a vacuum of information, nothing. Now consider that the towns are 26 miles apart. Suddenly, the two hours seems excessive. But the highway between the towns was blocked by a toxic spill cleanup operation for a time. Time explained. But the suspect had foreknowledge of the spill and a helicopter at his disposal... and on and on until all data which would lend meaning to the evidence is gathered. Has the reader guessed by this time what important special advantage Holmes possessed? It was no more nor less than this: His knowledge base encompassed everything that was known about anything anywhere in the world in the Victorian Era. He knew how paralytic poison manufactured from the sap of a tree which grew only in the Amazon Basin smelled. Every single clue in every case he ever worked bore upon some knowledge which he possessed, no matter how remote the source of that knowledge might seem. 'Nuff said? The further, and less important advantage with which he was blessed by his creator was that each clue, on the whole, was subject to only a single interpetation. Multiple datasets with regard to a single clue generally did not exist. The above brings us to the subject of Holmes' logical facility, or "deductive powers." These were generally assumed to be a feature of unmatched native intelligence (Never mind that Watson was made to appear downright feeble-minded from time to time, in order to show Holmes as brilliant by comparison). In fact, anyone of average intelligence or better can be trained to utilize "deduction" on a par with Holmes'. Here's how: