Newsgroups: comp.ai.philosophy,sci.philosophy.tech
Path: cantaloupe.srv.cs.cmu.edu!rochester!udel!gatech!howland.reston.ans.net!EU.net!uknet!newsfeed.ed.ac.uk!edcogsci!peru
From: peru@cogsci.ed.ac.uk (Peter Ruhrberg)
Subject: Re: McCarthy, Leibnitz's Law & Intension
Message-ID: <DBK6FH.5xq@cogsci.ed.ac.uk>
Organization: Centre for Cognitive Science, Edinburgh, UK
References: <ydnrb3y70lu.fsf@tahoe> <805469150snz@longley.demon.co.uk> <805473042snz@longley.demon.co.uk>
Date: Tue, 11 Jul 1995 15:45:15 GMT
Lines: 35
Xref: glinda.oz.cs.cmu.edu comp.ai.philosophy:29929 sci.philosophy.tech:18723

In article <805473042snz@longley.demon.co.uk> David@longley.demon.co.uk writes:
>A Retrospective View: July 1995
(stuff deleted)
>
>    I  think  it is important to point  out  that  Quine  is 
>    arguing that it is not a matter of taste how one  settle 
>    Brentano's  Thesis, but one forced upon us by logic.  He 
>    is  (unless  I  am very much  mistaken)  saying  that  a 
>    SCIENCE of intension is logically impossible,  partially 
>    because  all  of the intensional idioms,  including  the 
>    modal  operators, flout the basic laws of the  Predicate 
>    Calculus,  which  Quine takes *to be*  the  language  of 
>    science. With idioms such as 'said that x', one  can not 
>    substitute y for x even if y is co-extensive with x, and 
>    preserve the truth value of what was said. The same goes 
>    for  all of the propositional attitudes of  course.  Now 
>    this is entirely different in the language  of   science 
>    where  substitutivity  of identify  is  essentially  the 
>    means  whereby  we make deductive inferences.
>
>David Longley

I think it is time to get rid of the idea, floating in this newsgroup,
that science of the intensional is impossible because of the
substitutivity problem in intensional contexts. The bookshelves are
full of consistent intensional logics. The key point is what you take
for denotations, so the issue is ontological really. If you're happy
with possible worlds, or properties, you may even - oh wonder - use
1st - or whatever order - *extensional* logic to talk about them. (for
example basic modal logic is a fragment of FOL, via Kripke's
semantics; Bealers Property Theory is fully expressed in FOL; etc...)
The question is whether we want to live in Quines cold universe of
particles, sets, and double standards. 

Peter
