On 10/23/2016 09:59 AM, George Greene wrote:
> On Sunday, October 23, 2016 at 9:19:59 AM UTC-4, mitch wrote:
>> The power set of a given set is the set of all of its subsets.
>
> Fine so far, but SEZ WHO? In the usual case, sez THE POWERSET
> *AXIOM*. Whenever you say "must", you need to be clear "on whose
> authority". WHO SAYS this or that "must" be the case,and whey need
> THEY be respected?
>
I believe this would still be the power set
axiom. What is problematic for the model
theory is "all".
>> To be a subset, an individual must first be a set. So, every subset
>> of a set is necessarily a set.
>
> Fine, natural-language grammar, re the usual working of prefixes in
> English.
>
>> To be a set, an individual must be an element of the universe.
>
> This is getting dangerous. You have to pick a paradigm here. In the
> FOL paradigm, to BE, PERIOD, you "must be" an element of the
> universe. THERE IS NO OTHER KIND of JUST *be*ing! The "set" thing
> is just irrelevant. The universe by definition is just the class of
> all&only "those things that exist" and EVERY such thing "must be an
> element of the universe", sets and non-sets both.
>
Thank you. You have just made the argument that
philosophical treatments of set theory have an
underlying metaphysical basis even when the use
of uninterpreted symbols keeps one from making
ontological commitment.
To admit this position, however, would require a
change to the accepted axioms for Zermelo-Fraenkel
set theory to include urelements. Jech calls this
ZFA where the "A" stands for atoms. Among the
changes to set theory which may be attributed to
Skolem, the idea that the theory of pure sets
sufficed as a foundation for mathematics arose.
So, the "set" thing is relevant in some literature
and not in other literature.
Unfortunately, Jech does not write the axioms
out formally. What he does say is this:
< begin quote >
"Set Theory With Atoms (ZFA)
In this modified set theory we have not only
sets, but also additional objects, *atoms*. These
atoms do not have any elements themselves but can
be collected into sets. Obviously, we have to
modify the axiom of extensionality, for any two atoms
have the same elements -- none.
The language of ZFA has, in addition to the
predicate "in", a constant "A". The elements of
A are called *atoms*, all other objects are called
*sets*.
Axiom A. If a in A, then there is no x such that
x in A
The axiom of extension takes this form:
(21.1) If two sets X and Y have the same elements,
then X=Y
All other axioms of ZF remain unchanged. In particular,
the axiom of regularity [foundation] states that every
nonempty set has an in-minimal element. This minimal
element may be an atom.
The effect of atoms is that the universe is no
longer obtained by iterated power set operation from
the empty set. In ZFA, the universe is built up from
atoms.
Ordinal numbers are defined as usual except that
one has to add that an ordinal does not contain any
atom."
< end quote >
Jech goes on to explain how a cumulative hierarchy
for an arbitrary set is generated and then defines
the universe to be the cumulative hierarchy generated
from A.
In a very real sense, Russell's paradox is what
makes the "set" thing irrelevant. Where you told
Mr. DiEgidio that first-order logic carries existential
import by virtue of definition, what had been required
for modern compositional logics to be accepted had
been a representation for the square of opposition
in the new logic. So, in the translations,
All A are B
Ax( A(x) -> B(x) )
Some A are B
Ex( A(x) /\ B(x) )
No A are B
Ax( A(x) -> ~B(x) )
Some A are not B
Ex( A(x) /\ ~B(x) )
the predicate "A(x)" is what names the universe of
discourse as "number" or "set" or "philosophers".
For example,
All men are animals.
But, Russell's paradox showed that one could not
name "sets" in this manner if, by set, one meant
sets for which "x in x" does not hold.
Now, I happen to agree with your statement concerning
the paradigm and understand why you said it. But,
that does not mean that it is applied that way
uniformly in the literature.
Although I found Jech last night, I have not yet
found "Set Theory and the Continuum Hypothesis".
From that book I can quote the author interpreting
a "bare quantification" as "meaning" what I have
just said.
For what this is worth, I am not the author of
these conflicting views.
>> The sets of the cumulative hierarchy do not have complements. So,
>> a power set need not be a system of complements.
>
> Again, this is in THE USUAL treratment. In the usual treatment OF
> the cumulative hierarchy, the cumulative hierarchy DOES NOT EXIST
> because IT cannot fit "inside" itself.
>
The problem then are all of the references in
the literature using the expression,
"the universe"
or
"the set universe"
Without knowledge of the history of foundations,
I simply applied the notion of definite description
to this expression. More precisely, I asked
how I might be able to apply that notion. In any
case, the "epistemic warrant" of definite description
goes immediately to a syntactic version of Leibniz'
identity of indiscernibles. And, this is what has
been excluded from the standard account of identity
in the received paradigm of first-order logic.
If one is supposed to surmise non-existence from
paradox, why is the literature replete with such
uses that ignore the problem?
I am not trying to account for reality. A problem
in which I am interested is bound up in a great
deal of "vague" literature. Presumably the problem
is mathematical. Mathematical does not mean
metaphysical. But influential authors like Quine
have pursued mathematics as if it is.
I have no problem with your statement that the
cumulative hierarchy cannot fit inside of itself.
I have explicitly stated that Russell's paradox
forces the cumulative hierarchy to be partial.
But, that does not mean that the axioms cannot
be altered to add a denotation to the language
that acts as a container for the cumulative
hierarchy. It then becomes, like Ord of Card,
a class that is not representable in the
theory.
>> Holding as close as possible to the usual formulation of set
>> theory, the only sets that can be in the power set of the universe
>
> No, No, NO! As soon as you say "holding as close as possible to the
> usual formulation of set theory", you GIVE UP the right to speak of
> "the power set of the universe"!
What I mean by "as close as possible" is that the sets
which are not elements of themselves still be recursively
generated with respect to the axiom of foundation.
> The universe IS NOT a set and DOES
> NOT HAVE a powerset! The question of whether the universe is CLOSED
> under powerset (or not) IS COMPLICATED!
The latter statement is a somewhat trivial
observation.
> EVERY set has MORE subsets
> than members!
Have you ever tried to prove the theorem for
strict subsets without first invoking the
power set axiom and removing one element?
Because there is an ambiguity between singletons
and elements, my original first two sentences have
parallel syntax,
AxAy( x psub y <-> ( Az( y psub z -> x psub z ) /\ Ez( x psub z /\ ~( y
psub z ) ) ) )
AxAy( x in y <-> ( Az( y psub z -> x in z ) /\ Ez( x in z /\ ~( y psub z
) )
When I first tried to normalize the relationship I
needed a power set axiom,
AxEyAz( z in y <-> z psub x )
My approach had been naive and followed what is described
in Quine using a defined identity. But, that naive approach
included an axiom that violated pairing. More precisely,
only one singleton could exist in any model. But, any limit
ordinal could model the axioms.
In effect, the two predicates were being taken to be
equivalent. The power set was fixed for every element
of any model. Yet, all three of these sentences are
"true" in set theory.
Syntactic forcing is based upon introducing "truths" in
a particular order. So, once a formula is introduced,
its negation is excluded. In looking at these sentences,
I am not doing anything extraordinary.
But, since what I am doing is based on "defining one's terms",
it is very different from "undefined language primitives".
> YOU CAN'T PUT ALL the subsets of the universe into the
> universe as individuals! Well, you can put all its subSETS there,
> but NOT all its subCOLLECTIONS or subclasses! ONLY the subSETS and
> NOT the sub-PROPER-classes CAN HAVE powersets!!
>
Since I found Jech last night, I now have access
to the definition about which I questioned Rupert.
It reads as follows:
< begin quote >
"We say that a class M is *almost universal* if every
subset X of M is included in some Y in M. (Note that
M has to be a proper class.)
Theorem 31. Let M be a transitive, closed, almost
universal class. Then M is a model of ZF"
< end quote >
My question to Rupert lies with the word "included".
It it means "included as a subset", then would it
mean "included as an element" by virtue of the
power set axiom. Otherwise, it must mean "included
as an element" in some other element Y of M.
So, an "almost universal" class is precisely one
which contains all of its subsets as elements.
Of course, in the typical language, it is a proper
class. What I am trying to do is to create a
denotation for such a class by describing it as
one that is an element of itself.
Unless it can be included as a subset which does
not then appear in a power set, you are holding
me responsible for what is already in accepted
literature.
mitch