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From: jeff@aiai.ed.ac.uk (Jeff Dalton)
Subject: Re: Heliocentricism (Re: THE PURPOSE OF LIFE Defined & Gaia)
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Date: Fri, 27 Jan 1995 20:30:12 GMT
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In article <3g6utr$gcr@agate.berkeley.edu> <jerrybro@uclink2.berkeley.edu> writes:
>jeff@aiai.ed.ac.uk (Jeff Dalton) wrote:
>
>> Now, I don't think Galileo confined himself to the following (formally
>> invalid) argument: 
>> 
>>   "If the solar system is heliocentric, Venus will show moon-like
>>   phases".  Galileo observed that Venus shows moon-like phases;
>>   therefore, the solar system is heliocentric.
>
>I agree, Galileo in fact did not confine himself even to the
>argument which the above badly expresses.  But his
>arguments would be no more formally valid if he argued:
>
>If P then Q1, Q2, etc.
>
>Q1, Q2, etc.
>
>Therefore P.
>
>This is formally invalid.  And yet, the argument which this badly
>expresses can easily be a strong, persuasive one, given a suitably
>elegant P, and given the importance of Qi, and given that P does
>not conflict with much else.
>
>So the formal invalidity of the expressed argument is quite beside
>the point; it is a bad expression of an argument which can be quite
>strong.

The formal invalidity of the expressed arguement is quite beside
some points, sure; but it's not beside the points I was making.
(For instance, that it's not just benighted theologians "and others"
who find something wrong with affirming the consequent.)

Moreover, such arguements are not always poor expressions of
different good arguments.  Sometimes they're just fallacious
arguments that fail to justify their conclusions.

Note too that the theologians and others might well have found such
different, better arguments persuasive.  Of course, they probably
thought that Galileo's P did conflict with much else.  But what I was
answering was the idea that the theologians were rejecting Galileo's
argument because it was (by their lights) invalid.  They may well have
thought is was invalid (just as we would, if the argument were the one
given), but for them (just as for us) invalidity may not have been
the whole story.
