From: nguyen@drutx.ATT.COM (Christopher Chu)
Newsgroups: soc.culture.vietnamese
Subject: Re: [LOGIC]  Logic 101.
Summary: This is indeed logic 101 which I would preferably call "make believe."
Date: 30 Jul 92 09:02:26 GMT
Organization: AT&T Bell Laboratories - Denver, Colorado


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| Dear SCV readers,                                                          |
|                                                                            |
| I must say that the article on which I am commenting is indeed a           |
| representative example as how logic has been used by people who only know  |
| it on the surface. I welcome comments from interested readers on this      |
| article.                                                                   |
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| | From: longn@lauto.lmc.com (Long Nguyen)                          |       |
| | Newsgroups: soc.culture.vietnamese                               |       |
| | Subject: [LOGIC]  Logic 101.                                     |       |
| | Message-ID: <m0mDOIR-30CdGwC@lauto.lmc.com>                      |       |
| | Date: 30 Jul 92 01:23:00 GMT                                     |       |
| |                                                                  |       |
| | I found this exchange between two Americans on a net.            |       |
| | Posted without permission.                                       |       |
| |                                                                  |       |
| | Longan - the Logician                                            |       |
| |                                                                  |       |
| | P.S.  I wonder how many troops attempting the 2 logic puzzles?   |       |
| |                                                                  |       |
| | >   All murderers have human form                                |       |
| | >   You have human form                                          |       |
| | >                                                                |       |
| | >   You must be a murderer                                       |       |
| |                                                                  |       |
| | No offense intended, Tom, but this logic is flawed.              |       |
| | A -> B                                                           |       |
| | A                                                                |       |
| | therefore B is correct, or                                       |       |
| | A -> B                                                           |       |
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| ~B <-- We need this right here for what follows to make sense!!!           |
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| | therefore ~A                                                     |       |
| |                                                                  |       |
| | (All murderers have human form.                                  |       |
| | You are a murderer, therefore you have human form.               |       |
| | or                                                               |       |
| | All murderers have human form.                                   |       |
| | You do not have human form, therefore you are not a murderer...) |       |
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| First, at the subconscious level, we may attempt to show that there was,   |
| somehow, fallacy in Tom's reasoning by reminding him that there are        |
| non-murderers who also have human form!!! I think logician specially       |
| dedicate the term "counter example" for this kind of fallacy detection.    |
|                                                                            |
| Second, I must comment that the person who responded to Tom, sorry to say, |
| did not seemed to grasp the fallacy. His explanation using symbolic        |
| presentations indicated that he was not clear why Tom's argument was in    |
| fact invalid. He formulated Tom's reasoning as follows:                    |
|                                                                            |
|	A->B: If you are a murderer, then you have the human form.           |
| where                                                                      |
|	A: You are a murderer.                                               |
|	B: You have human form.                                              |
|                                                                            |
| and progressed to state that if A->B and A were true then B was true or if |
| ~B and ~B->~A were true then A was also true. What was stated is too true  |
| to be stated at all!!! Finally, the person did not explain say why Tom's   |
| reasoning was invalid!!! How confusing an unclear argument that was to be  |
| against another unclear argument could be!!!                               |
|                                                                            |
| In essence, the fallacy in Tom's reasoning was due to the fact that Tom    |
| thought the English statement "All murderers have human form" was in fact  |
| *logically equivalent* to the logical conditional predicate "If you have   |
| the human form, then you are murderer." That would be the only reason why  |
| he said "You have human form" [therefore,] "You must be a murderer."       |
|                                                                            |
| If Tom thought carefully, he might be able to realize that the conditional |
| predicate above is exactly what he wanted to prove. Unfortunately, Tom     |
| stated what he wanted to prove ambiguously with English and made believed  |
| that he had reasoned it. Tom's reasoning and the response from the other   |
| person are probably the two shortest articles that represent how abusively |
| logic has been used on this net. I think logician specially dedicate the   |
| term "begging the question" for Tom's kind of fallacy; this is, by and     |
| large, one among the two most common causes of logic abuse in the human    |
| reasoning process.                                                         |
|                                                                            |
| I think the lesson to be learned here is that logic is not only about the  |
| mechanics of symbolic manipulation itself (e.g., memorization of logic     |
| definitions and simple logical computation based on truth tables); I think |
| this is only logic on the surface. In my opinion, the other part of logic  |
| training should be about the human ability to translate English arguments  |
| into the appropriate and correct symbolic presentation of logic and vice   |
| versa. How? I guess that we have to really understand logic in order to    |
| make it right.                                                             |
|                                                                            |
| Finally, I thank you all for providing me with an appropriate opportunity  |
| to state my comments. I guess that my references are any undergraduate     |
| text books about techniques of formal reasoning. One among the authors     |
| that wrote one of the books I read for an introductory philosophy course   |
| at UCLA in 1983 was Dr. Donald Kalish. In case readers are interested about|
| logicians themselves, Dr. Kalish was a student of Dr. A. Church, who was   |
| the head of the philosophy department at UCLA in the 80's. Dr. Church is   |
| one among the all-times famous logicians born in this century. His famous  |
| thesis hypothesized that Turing computability is the exact mathematical    |
| model for the human intuitive notion of the computer.                      |
|                                                                            |
| Sincerely Yours,                                                           |
|                                                                            |
| Chris Chu, nguyen@drutx.ATT.COM (Internet), att!drutx!nguyen (UUCP)        |
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Newsgroups: soc.culture.vietnamese