LW - Sherlockian Abduction Master List by Cole Wyeth

The Nonlinear Library: LessWrong

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Welcome to The Nonlinear Library, where we use Text-to-Speech software to convert the best writing from the Rationalist and EA communities into audio. This is: Sherlockian Abduction Master List, published by Cole Wyeth on July 13, 2024 on LessWrong.
[Radically updated with many new entries around 07/10/24]
Epistemic status: The List has been tested in the real world by me (with mixed results) and extensively checked for errors by many commenters. The Background section is mostly speculation and anecdotes, feel free to skip to The List once you understand its reason for existence.
tldr: This is a curated list of observable details about a person's appearance that indicate something useful/surprising about them. Ideally, studying this list will be an efficient way to cultivate more insightful observational/abductive abilities, approaching the fictional example of Sherlock Holmes. Please contribute in the comments section after reading the Rules.
Background
Is it possible to develop observational abilities comparable to Sherlock Holmes?
Sir Arthur Conan Doyle's fictional detective has many enviable skills, including mastery of disguise and some expertise at unarmed combat, as well as generally being a genius, but we will focus primarily on his more well known observational power. Though Holmes is often described as a master of logical "deduction," this power is better described as (possibly superhuman) abduction. That is, Holmes perceives tiny details that many people would miss, then constructs explanations for those details.
By reasoning through the interacting implications of these explanations, he is able to make inferences that seem impossible to those around him. The final step is actually deductive, but the first two are perhaps more interesting. Holmes' ability to perceive more than others does seem somewhat realistic; it is always possible to actively improve one's situational awareness, at least on a short term basis, simply by focusing on one's surroundings.
The trick seems to be the second step, where Holmes is able to work backwards from cause to effect, often leveraging slightly obscure knowledge about a wide variety of topics.
I spent several of my naive teenage years trying to become more like Holmes. I carefully examined people's shoes (often I actually requested that the shoes be handed over) for numerous features: mud and dirt from walking outside, the apparent price of the shoe, the level of wear and tear, and more specifically the distribution of wear between heel and toe (hoping to distinguish sprinters and joggers), etc. I "read palms," studying the subtle variations between biking and weightlifting calluses.
I looked for ink stains and such on sleeves (this works better in fiction than reality). I'm pretty sure I even smelled people.
None of this worked particularly well. I did come up with some impressive seeming "deductions," but I made so many mistakes that these may have been entirely chance.
There were various obstacles. First, it is time consuming and slightly awkward to stare at everyone you meet from head to toe. I think there are real tradeoffs here; you have only so much total attention, and by spending more on observing your surroundings, you have less left over to think. Certainly it is not possible to read a textbook at the same time, so practicing your observational techniques comes at a cost.
Perhaps it becomes more habitual and easier over time, but I am not convinced it ever comes for free.
Second, the reliability of inferences decays quickly with the number of steps involved. Many of Holmes' most impressive "deductions" come from combining his projected explanations for several details into one cohesive story (perhaps using some of them to rule out alternative explanations for the others) and drawing highly non-obvious, shocking conclusions from this story.
In practice, one of the explanations is usually wrong, the entire story is base on false premises, and the conclusions are only sh...