FOM: corresponding?
Randall Holmes
holmes at catseye.idbsu.edu
Tue Mar 23 12:14:18 EST 1999
I didn't notice the following aspect of Kanovei's note.
He said:
Apparently, the only mathematical point here is that
some properties of mathematical structures S,
not expressible in the *corresponding* 1st-order
language,
become expressible if quantification
over P(S) is allowed.
I reply:
No, not expressible in _any_ first-order language. The property of
being a model of true arithmetic is not expressible at all in any
first-order theory, however strong. (In the following sense: any
first-order theory which describes a certain structure S in its domain
in terms compatible with S being a model of true arithmetic has models
in which S is in fact not a model of true arithmetic).
The issue here is entirely one of what one can define or express;
one gains nothing in terms of proof machinery which cannot be gained
by working in a stronger first-order theory. The point which is
being belabored is that the reference of mathematical language is
an important foundational issue.
And God posted an angel with a flaming sword at | Sincerely, M. Randall Holmes
the gates of Cantor's paradise, that the | Boise State U. (disavows all)
slow-witted and the deliberately obtuse might | holmes at math.idbsu.edu
not glimpse the wonders therein. | http://math.idbsu.edu/~holmes
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