[hist-analytic] The "Analytic A Posteriori"
danny.frederick at tiscali.co.uk
Wed Sep 2 17:03:19 EDT 2009
Excuse me if I have got it wrong, but it seems to me that what you want to
say is that 'a=b' is empirical and 'if a=b, then Nec a=b' is a priori. When
you combine the two you get the conclusion 'Nec a=b,' which therefore
combines empirical and a priori.
A view of this kind is espoused by Peacocke here:
If my memory is correct (it might not be), Gareth Evans put forward a
similar view ('Varieties of Reference' I would guess - but I've not read it
for more than 20 years). I don't accept the view myself, of course.
I also do not accept the principle 'if a=b, then Nec a=b,' UNLESS a and b
are necessary existents. My assumption here is that 'a=b' is false (or, at
least, not true) if a or b does not exist. So if a or b is a contingent
existent, a=b must be contingent.
I think Bruce made a valid point. 'The cat is fat v ~the cat is fat' is
necessarily true, quite independently of the truth or falsity of 'the cat is
fat.' But 'Nec a=b' has no chance of being true if a=b is false (even
ignoring the issue about contingent existence).
I think you are mistaken in affirming that even if the designators are not
rigid 'Nec(a=b)' follows from a=b by first order logic by substitution of
predicates. Consider a specific example. The inventor of bifocals = the
first postmaster general. This says (according to Russell) that there is
just one person who both invented bifocals and was the first postmaster
general. Even supposing it is true, it does not follow that it is
necessarily true that just one person did these two things; in fact it seems
plainly possible that two different people might have invented bifocals and
been the first postmaster general, even if ion fact one person did both.
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