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Author: Don HDon H Date: Oct 9, 2006 14:32
> [T]he "deductions" of Sherlock Holmes: I have ... been interested in
> the discrepancy between "deduction" in detective mysteries and
> "deduction" in the logic books. Doyle's use of the word "deduction"
> only reflects how the word has been commonly used--not only by ordinary
> people, but also by educated people. To most people, any kind of
> inference is a "deduction."
>
> I don't see that it helps to say that the common usage is "wrong" and
> that the technical usage is "right." I would think that if one is
> knowledgeable on a certain subject and wants to convey that information
> to others, it would be best to point out that within that subject
> matter the use of a word differs from common usage.
>
> If I tell someone that I have "deduced" something, they think they know
> what I mean. If I talk to someone about "induction," I have lost them.
> They think they know what I mean if I talk about "learning from
> experience." As with so many difficult words, one problem with
> "induction" is that the word has been used in so many different ways. ...
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Author: TronTron Date: Oct 11, 2006 16:03
> [T]he "deductions" of Sherlock Holmes: I have ... been interested in
> the discrepancy between "deduction" in detective mysteries and
> "deduction" in the logic books. Doyle's use of the word "deduction"
> only reflects how the word has been commonly used--not only by ordinary
> people, but also by educated people. To most people, any kind of
> inference is a "deduction."
>
I think that says it all. To "deduce", and never mind if it is a de-, an ab-
or an induction - is used as a shorthand for the verbal phrase "arriving at
a conclusion by the use of logic"; or, IOW, as the verb to the noun "logic".
It is more of a metonymy - a pars pro toto - than an attempt to specify any
particular logical form. Tropical language - hard to avoid.
T
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Author: ImmortalistImmortalist Date: Oct 9, 2006 11:48
[T]he "deductions" of Sherlock Holmes: I have ... been interested in
the discrepancy between "deduction" in detective mysteries and
"deduction" in the logic books. Doyle's use of the word "deduction"
only reflects how the word has been commonly used--not only by ordinary
people, but also by educated people. To most people, any kind of
inference is a "deduction."
I don't see that it helps to say that the common usage is "wrong" and
that the technical usage is "right." I would think that if one is
knowledgeable on a certain subject and wants to convey that information
to others, it would be best to point out that within that subject
matter the use of a word differs from common usage.
If I tell someone that I have "deduced" something, they think they know
what I mean. If I talk to someone about "induction," I have lost them.
They think they know what I mean if I talk about "learning from
experience." As with so many difficult words, one problem with
"induction" is that the word has been used in so many different ways.
"Induction" might mean:
* To elicit a theory.
* To verify a theory.
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Author: extropy1extropy1 Date: Oct 9, 2006 11:51
Sherlock Holmes and Probabilistic Induction
(Q0) "From a drop of water," said the writer, "a logician could infer
the possibility of an Atlantic or a Niagara without having seen or
heard of one or the other. So all life is a great chain, the nature of
which is known whenever we are shown a single link of it. Like all
other arts, the Science of Deduction and Analysis is one which can only
be acquired by long and patient study, nor is life long enough to allow
any mortal to attain the highest possible perfection in it. " [A Study
in Scarlet, pt. 1, ch. 2] Sherlock Holmes.
We can find many words in Holmes stories which may be used as an
evidence for showing that he was a logician. First of all, he
frequently characterizes himself as a logician. Quotation Q0 is one of
such examples. Here, he speaks of what a logician can do, as well as of
what a logician should do. It is certainly a typical task of a logician
to do "deduction and analysis," and he or she should work hard in order
to be a good logician!
And secondly, many of his words clearly show his stance as a logician.
The following quotations are typical examples:
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Author: Arturo MagidinArturo Magidin Date: Oct 9, 2006 12:02
>[T]he "deductions" of Sherlock Holmes: I have ... been interested in
>the discrepancy between "deduction" in detective mysteries and
>"deduction" in the logic books. Doyle's use of the word "deduction"
>only reflects how the word has been commonly used--not only by ordinary
>people, but also by educated people. To most people, any kind of
>inference is a "deduction."
As I recall, "deduction" means reaching conclusions about particulars
given general principles. "Induction" means to reach conclusions about
generalities given particulars.
Holmes is using deduction, because he goes from general principles
(e.g., that wearing a certain kind of hat denotes frugality) to
deducing things about the specific person or situation in front of
him.
However, these are not the ways in which "deduction" and "deducing"
are used in everyday language. Mostly because people don't know the
technical meaning of the terms.
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Author: ImmortalistImmortalist Date: Oct 10, 2006 09:22
Peter_Smith wrote:
> Holmes's reasonings are usually "inferences to the best explanation".
> Here's some data (in the best sort of story, a very puzzling
> combination of data that "makes no sense"). Then here's an explanation
> (which makes everything fall into place).
>
> But it is (usually) at least logically possible that the explanation is
> false. (That logic point is exploited by post-Holmsian stories where an
> apparently convincing explanation of the murders is arrived at, only
> for another murder to happen when the initially accused has a cast-iron
> alibi.) If we use "deduction" in the logician's sense of absolutely
> watertight inference -- where if the premisses are true, it is simply
> impossible for the conclusion to be false -- then the detective's
> "deductions", i.e. his...
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Author: ImmortalistImmortalist Date: Oct 10, 2006 09:24
Arturo Magidin wrote:
>>[T]he "deductions" of Sherlock Holmes: I have ... been interested in
>>the discrepancy between "deduction" in detective mysteries and
>>"deduction" in the logic books. Doyle's use of the word "deduction"
>>only reflects how the word has been commonly used--not only by ordinary
>>people, but also by educated people. To most people, any kind of
>>inference is a "deduction."
>
>
> As I recall, "deduction" means reaching conclusions about particulars
> given general principles. "Induction" means to reach conclusions about
> generalities given particulars.
>
> Holmes is using deduction, because he goes from general principles
> (e.g., that wearing a certain kind of hat denotes frugality) to
> deducing things about the specific person or situation in front of
> him.
> ...
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Author: ImmortalistImmortalist Date: Oct 10, 2006 09:34
Don H wrote:
>> [T]he "deductions" of Sherlock Holmes: I have ... been interested in
>> the discrepancy between "deduction" in detective mysteries and
>> "deduction" in the logic books. Doyle's use of the word "deduction"
>> only reflects how the word has been commonly used--not only by ordinary
>> people, but also by educated people. To most people, any kind of
>> inference is a "deduction."
>>
.....>
>>
>
> # You could almost devote an entire chapter in a book on logic to "the art
> of detective reasoning".
> How does a "detect-ive" function?
> A "crime scene" involves a mystery...
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Author: Don HDon H Date: Oct 10, 2006 12:41
>
> Peter_Smith wrote:
>> Holmes's reasonings are usually "inferences to the best explanation".
>> Here's some data (in the best sort of story, a very puzzling
>> combination of data that "makes no sense"). Then here's an explanation
>> (which makes everything fall into place).
>>
>> But it is (usually) at least logically possible that the explanation is
>> false. (That logic point is exploited by post-Holmsian stories where an
>> apparently convincing explanation of the murders is arrived at, only
>> for another murder to happen when the initially accused has a cast-iron
>> alibi.) If we use "deduction" in the logician's sense of absolutely
>> watertight inference -- where if the premisses are true, it is simply
>> impossible for the conclusion to be false -- then the detective's
>> "deductions", i.e. his inferences to the best explanation, are not
>> deductions. (Of course, it's just by conventional stipulation that
>> logicians nowadays use "deduction" in the narrow sense: what matters is
>> the distinction that is thereby marked between inferences to tbe best ...
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Author: ImmortalistImmortalist Date: Oct 12, 2006 10:34
Don H wrote:
>>
>> Don H wrote:
>>>>
>>>> Peter_Smith wrote:
>>>>> Holmes's reasonings are usually "inferences to the best
> explanation".
>>>
>>>
>>> # Word, words, words - we humans are apes who like to monkey about with
>>> words, which are artefacts used to describe empirical reality.
>>> All of us go primarily by observed fact, and make deductions from it. ...
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