What Sherlock Holmes Got Wrong | Deduction, Induction, and Abduction

Sherlock Holmes is famous for his deductions. But what if they're not deductions at all?

00:00 Introduction
00:24 Deduction
00:57 Do deductions move from the general to the particular?
01:39 The key characteristic of deductions
02:21 Induction
02:45 Do inductions move from the particular to the general?
03:21 The key characteristic of inductions
04:26 A special kind of induction
05:35 Semantics?

Reference:

The best discussion of the distinction between the three kinds of reasoning I outlined here comes from "How We Reason" by Philip Johnson-Laird - cognitive scientist extraordinaire. Chapter 13 is on Sherlock and abductions. It's his model that I'm describing.

The clips are from the BBC series "Sherlock," starring Benedict Cumberbatch. Used here for educational purposes.

[loremipsum]

Your video reminded me of a statement on cognitive capabilities in the Sherlock Holmes novel "A Study in Scarlet". Holmes states that a brain's memory space is limited and he thus only remembers about stuff which he considers important for his detective work (and forgets everything else). I've pondered about the statement quite some time since it deviates from my personal experiences, and would be interested what you as an expert in this field say on it.

The original text is: "I consider that a man’s brain originally is like a little empty attic, and you have to stock it with such furniture as you choose. A fool takes in all the lumber of every sort that he comes across, so that the knowledge which might be useful to him gets crowded out, or at best is jumbled up with a lot of other things, so that he has a difficulty in laying his hands upon it. Now the skillful workman is very careful indeed as to what he takes into his brain-attic. He will have nothing but the tools which may help him in doing his work, but of these he has a large assortment, and all in the most perfect order. It is a mistake to think that that little room has elastic walls and can distend to any extent. Depend upon it there comes a time when for every addition of knowledge you forget something that you knew before. It is of the highest importance, therefore, not to have useless facts elbowing out the useful ones."

[GustavoSilva-nyjc]

2:21 This is actually MIND BLOWING in galactical proportions cause it makes so much sense!!!! Especially in the modern "tamed" world. Cause if you never saw any variation of something you will logically and intuitively believe, many times without consciously thinking, that you have figured it out and never will see something different. There's also our IRRITATING notion of separating things in "normal" and "not normal" even though it's totally arbitraty, it's what makes uncanny pictures go viral from time to time (momo was her name?) and horror genre exist. The swan analogy is really a wake up call, i like Dr. Stone approach to magic/superpowers, "it's not magic cause we dont understand and challenge our assumptions of the world!!! It's just how it is or always were and we're just learning now! We're touching a totally unknown field of science, isnt exhilirating?!" Magic is still science, we just discovered we were too overconfident.

That's why LOOOOVE lies, detectives, magic, conman and gambling cause that's what's human life is, we're experts at making idiots of ourselves and i think guys who make fooling people and exposing this for are living are better searchers of truth than scientists (extreme, i know, but there's something with things like death note that i dont see anywhere, and i think the use of machines and other disciplines is what give science an edge, as well more people doing and/cause it's more socially acceptable).

[felipetolomio]

Aduction? Thank you. Student nurse, makes me think of diagnosis where it would be helpful to learn about the process of aduction which would provide an explanation for a symptom rather than just a deduced statement about the condition. E.g. the patient is limping therefore he must have something wrong with his leg is a deduction but moving forward with that an aduction would be explaining why there is something wrong with the patient's leg bringing the nurse practitioner closer to a useful cause and eventually diagnosis.

[Bahamamos]

I have OCD and it typically is over topics and observations. Abductive reasoning similar to Sherlock, but not into a fantasy level like in the novel, of course. What I see in my head and what he's probably calculating is shortening the probability of what it couldn't be into what it could be, which is why it corrects himself mid-sentence sometimes. It's like math without math, and basing it off of people's region at times. I can even guess a person's accent and get the specific area of a country; the various areas of California (valley, bay, hollywood, the hood(s)) or other parts in America (Alabama and Tennessee sound different), China (Mandarin and Catonese), UK (birmmingham-hood, London, South London), etc. And it helps if I'm incorrect to build exp. My most precise was to someone at work: "You sound like you come from the bay area, but lived in the south for a bit later in life" and they said how did I know, and most think he sounds southern and was surprised he could hear the bay accent in his twang. I was diagnosed at age 3 of OCD, and it's a gift and a curse.

[jpegmfia]

Thank you for this video! I’ve been watching BBC Sherlock and every time they say “deduction” I want to rip my hair out lol

[GustavoSilva-nyjc]

The best story who avoids the phone scene is Akagi, especially though the perspective of washizu, akagi toys with his tendency for comfirmation so much that even when he tries to disconfirm he's toyed, apply calling akagi as the Devil after a point. "INSANE!!!! This is insane!!!! Even if i try to think or not to think i ended up ALWAYS giving what he wants!!! Why i always do that?!"

[alexandersen]

I have an exam next month in scientific theory. And this was useful. Thank you 👌🏼🧐☺️

[knw-seeker]

Could you make also a video about how with your experience as a learning scientist
would prepare for a school, college or university exam?

[Vacuous]

The only way to approach the deduction is by applying all the rules of inference, and replacement. Deduction also produces 2 kinds of arguments that is valid and ivalid if the deduction produces the argument with the conclusion follow the premises, the argument is valid if and only if the conclusion must be true if isn't true then the argument is invalid.Note that if argument is valid doesn't mean it sound but the invalid argument always unsound even if you apply modus ponen correctly that is
If P1 then P2
P1
Therefore P2
Doesn't guarantee you will ended up in sound and valid argumen here's an example:
(1) All wines are soft drink (Premise)
(2)Ginger ale is a wine(Premise)
(3)Therefore, Ginger ale are soft drink (1, 2 modus ponen)
Is this argument valid and sound?the answer it's valid and unsound since it has false premise eventhough the conclusion is true but if we change the premises however:
(1)All wines are beverage(Premises)
(2)Chardonnay is a wine (Premises)
(3)Therefore, Cahrdonnay is a beverage (1, 2 Modus Ponen)
This is a valid and sound argument by modus ponen yet the 'Deduction' that Holmes use even doesn't touch the most basic rules of inference nor single any of rules of inference and replacement, if the argument that use the rules of inference still have a big chance to have false premises and unsound what would you expect from the argument that doesn't use single of them?

[GustavoSilva-nyjc]

1:07 Funnily enough, this is also done by superforecasters, Tetlock stresses that they start with the broad statistics and then look at the particular details, people do the other way around, i mean, it isnt more logical???? Who cares if the difference in number from farmers to librarians is 9/1 THIS GUY SCREAMS LIBRARIAN!!!! And yet they dont, or are informed to, not think that way. I guess if you can/have time, it doesnt hurt to reason this way 1st and then go with your "intuition" if it still feels more accurate.

[NorikaKizawa]

Deduction: nothing to add
Induction :adding information, which might be wrong.

[ABC-jqve]

Is deduction basically axiom based reasoning? I don’t understand why they needed to invent a new term for this when math has been doing this forever.

[EsotericArnold]

Lol once you see it, you can't unsee it. I guess most problem solving shows follow the same pattern, then. Pass off abduction as deduction .

[panchofenix]

do you still hold your posture expressed on this video to this day?

[englishwithanes]

Ok I've got a biased deduction and you will tell me where I got it wrong 👍🏻

1- what is rare is expensive
2- a cheap horse is rare
3- thus, a cheap horse is expensive !!

Doesn't make sense 😜