Bruno Marchal wrote: > On 02 Jul 2009, at 21:37, Brent Meeker wrote: > > >> John Mikes wrote: >> >>> Brian, >>> I started to read the text and found the 1st sentence: >>> >>> /"In modern cosmology, a / >>> >>> /multiverse is defined to be a collection of possible physical >>> universes"/ >>> >>> that pissed me off: 'possible' in our today's sense includes many >>> 'impossibilities' in the sense of a mindset of 1000 years ago and I >>> assume does NOT include lots of 'possibles' in the scientific(?) >>> mindset >>> 1000 years hence. >>> >>> I find the position a 'present-day restricted' reductionist approach >>> adjusted into our 2009(or earlier?) cognitive inventory of physics. >>> >>> In rigorous science I could not do better, but is it a position you >>> would really deem a "a very interesting read"? >>> >>> JohnM >>> >> I agree with JM. Whenever I read the word "possible" I feel the >> intellectual >> ground shift and I look for a hand hold in case it turns to quicksand. >> > > > That is why we are invited to dig a bit in modal logic, which is a > tool for making the reasoning on possibilities more solid. > But then, with the comp hyp, we are lead to the arithmetical > possibilities, which can be made transparently clear. > > Like George Boolos explains in his 1979, and 1993 books, the critics > by Quine and Marcus on modal logics, just does not work for the > arithmetical possibility, which is consistency (or the arithmetical > necessity, which is provability). > > Bruno > > http://iridia.ulb.ac.be/~marchal/ Right. I have no problem with arithmetical possibilities, provability, etc. But without some defined scope the use of "possible" makes me uneasy. In modal logic "possible" and "necessary" are just operators that must be interpreted in some domain; just like "some" and "for all".
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