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From: esot@troi.cc.rochester.edu (Eric Sotnak)
Subject: Re: Heliocentricism (Re: THE PURPOSE OF LIFE Defined & Gaia)
Message-ID: <1995Jan26.005142.21523@galileo.cc.rochester.edu>
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References: <ONEAL.95Jan19201224@trantor.astro.psu.edu> <D2uCDI.CoK@cogsci.ed.ac.uk> <3fvtr9$qdg@agate.berkeley.edu> <D2z330.3DM@cogsci.ed.ac.uk>
Date: Thu, 26 Jan 95 00:51:42 GMT
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In <D2z330.3DM@cogsci.ed.ac.uk> jeff@aiai.ed.ac.uk (Jeff Dalton) writes:

>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.

  Indeed he did not.  Rather, the arg. is roughly this:  "If the
Aristotelian view of the natures of celestial objects is correct, then Venus
is self-illuminating.  If venus is self-illuminating, then it does not show
phases.  Venus does show phases.  Therefore the Aristotelian view of the
natures of celestial objects is (at least in part) incorrect."

  For the most part, Galileo concerned himself more with showing the
inadequacy of the Aristotelian cum-Ptolemaic model of the heavens (and of
Aristotelian physics in general) than with advancing a positive case for
heliocentrism.  The latter was, rather, a default model (Galileo seems not
to have considered seriously anything like the Tychonic model).

-- 
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