Re: The Logic of "if" and "if and only if"
From: LookinBob (rbb2_at_att.net)
Date: 11/17/04
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Date: Wed, 17 Nov 2004 07:23:58 GMT
The statement "Mary will eat pudding today if it's custard" gives Mary
a bit more personality and freedom of will than "Mary will eat custard
today," which could be said to imply that Mary has no choice in the
matter.
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On Sun, 07 Nov 2004 21:27:15 GMT, Mike Bluett <protected@vapour.net>
wrote:
>I am trying to get get to a basic level of understanding with regard to
>Numerical Analysis and keep running into perception obstacles (or
>possibly poorly phrased or improperly argued obstacles).
>
>For example, there is a "logic" example on www.wikipedia.org as follows:
>
>"Mary will eat pudding today if it's custard."
>
>The analysis for this statement, at Wikipedia, is as follows:
>
>"Sentence (1) only states that Mary will eat custard pudding. It does
>not however preclude the possibility that Mary might also be prepared to
>eat bread pudding. Maybe she will, maybe she won't. The sentence does
>not tell us. All it tells us is that we can safely assume that she won't
>refuse custard pudding today."
>
>It seems to me this argument is flawed.
>
>The only reason for making such a statement as "Mary will eat pudding
>today if it's custard." is to tell someone that "custard" is the only
>pudding Mary is prepared to eat today. Therefore, it must be implied
>that all other puddings must be excluded as possibilities.
>
>If I wanted to create a statement that aligns itself to the argument, as
>stated on the Wikipedia site, it would be "Mary will eat custard today."
>(ie, there is no point in adding "if").
>
>Is the Wikipedia statement "Mary will eat pudding today if it's
>custard." just a bad example of when to use "if" as opposed to "if and
>only if"? If so, please provide me with a good example of why "if and
>only if" is required.
>
>OR, if it is a good example, then I don't see the necessity of using "if
>and only if" as I have tried to suggest.
>
>Comments?
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