Here are three skills that Sherlock Holmes (and Patrick Jane) possess that guide their art of deduction.

1) Ability to read body language.
This is a recognized science. It's the ability to judge what someone is thinking/believing by observing how they sit, how they stand, how they move their face. People lie with their talk, but their gestures very rarely lie. For instance, someone telling a lie is likely to pull their ear or try to hide their mouth behind their hand. Someone may say "Oh yes I like this" but their facial expression (ie swallowed a lemon) shows what they really feeling about this. Sherlock and Jane watch for these expressions. They know how to read them. There is nothing feng shu (etc) in this; reading people's thoughts/feelings from their expressions (and body language) is perfectly legitimate. I believe anyone can learn to do it. Sherlock and Jane are masters at it. A useful book about learning to read/decipher body language is "Body Language" by Alan Pease - it has plenty of relevant illustrations and is written in 'layspeak' not scientificise.


2) Up to date knowledge of current affairs.
Holmes (and to a degree Jane) are fully aware of what is happening around them in the world. Remember Holmes' "commonplace books" where he keeps newspaper clippings from the 'personal' columns and so forth? And his own personal wikipedia in the form of a compendium of criminals ("my collection of Ms is a fine one; Moriarty is enough to make any letter illustrious")? Holmes can draw connections that lead to solutions BECAUSE he knows the whole story. And part of his particular skill is being able to see which incidents are related to which other incidents.

Remember the "Case of the Engineer's Thumb"? One engineer is nearly murdered and (via Watson) comes to Holmes for help. Holmes brings out his commonplace book and points to one of his newspaper clippings. Some time before, another engineer had gone missing. That disappearance (said Holmes in other words) was the last time the villains who kidnapped you needed their pressing machine serviced. But if Holmes hadn't read the personal column, and kept that notice, could he have drawn the connection? This is part of the art of deduction - not being ashamed to keep newspaper/current affairs clippings BECAUSE who knows quite what they will help you solve in future.


3) Ability to see patterns, of behavior, of circumstances etc AND not dismissing a deduction 'because it doesn't seem very nice'.
Sherlock Holmes (and to a degree Patrick Jane) CAN 'think the unthinkable' without 'turning into monsters/going to pieces' etc. They don't overlook the UNusual suspects. Also they don't dismiss someone as a suspect (etc) 'just because it isn't particularly nice to think THAT might be so'. Remember when Jane solved a series of murders in a country club, because he was prepared to 'think the unthinkable' - ie that one of the Respectable Members of the Club might be the culprit? Sherlock and Patrick know that part of the art of deduction is using one's intuition and using one's knowledge NOT BEING DICTATED BY ONE'S (OR SOCIETY'S) PREJUDICES.


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