FOM: f.o.m. and the concept of set
wtait@ix.netcom.com
wtait at ix.netcom.com
Sun Jan 25 10:14:50 EST 1998
A remark about the relationship between foundations and set theory: An
old-fashioned conception of foundations is, roughly, that it is concerned
with finding the right axioms. Set theory then is the locus of 2
problems in f.o.m.: CH and Transfinite numbers. In the case of
transfinite numbers, the task of finding the right axioms is never
completable, since whatever axioms S we accept, we should be willing to
take as a further axiom the existence of a model for S. (Zermelo 1930
states this principle.) This problem is tied to set theory in at least 2
ways: First, with the system of transfinite numbers is associated the
cumulative hierarchy of sets iterated along the system of transfinite
numbers. It is natural to think of the axioms that we might introduce for
the existence of new numbers as formulated in the language of this
hierarchy of sets. Second, the question of what numbers we admit is
equivalent to the question of what totalities of numbers we admit as sets
(since to admit it as a set is to admit its lub as a number and
conversely.)
I want to emphasize that this is not an argument for `set theoretic
foundations' over `category theoretical foundations'. I simply want to
recall a fact, of which everyone is aware, but which has sometimes been
lost in recent discussions, viz. that the concept of set is intimately
implicated in leading problems in (old-fashioned) f.o.m. The issue is NOT
whether the language of categories could replace the language of set
theory in formulating axioms e.g. about transfinite numbers.
I do wonder whether the very extensive debate on the list over set
theoretic vs category theoretic foundations is something more than a
debate about rhetoric, about which of equivalent languages one should use
to, e.g., write textbooks on analysis for school children or whomever.
Bill Tait
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