On 25/08/2012 11:16 AM, Frederick Williams wrote:
> Nam Nguyen wrote:
>>
>> On 24/08/2012 12:50 PM, MoeBlee wrote:
>
>>> Then what is your technical definition of "impossible"?
>>
>> OK. Here is it, regarding to a _meta assertion_ P.
>>
>> Def1a. "It's possible to know, to assert the (meta level) truth value
>> of P" <=> "The truth value P _is in_ the collection of valid
>
> Is that meant to be "The truth value of P..."?
Right. It was a ridiculous kind of typo that somehow escapes
my attention from time to time. (And I really hate it!).
>
>> meta inference outcomes, using only FOL valid definitions,
>> assumptions, inferences (first order level or otherwise),
>> or otherwise valid, non-contradicting reasoning tools,
>> available within FOL reasoning framework".
>
> Because if it is, the truth value of P (supposing that it has one) is in
> {true,false};
Right,
> it is not in "the collection of valid meta inference
> outcomes". Surely the latter is just the set of meta theorems, isn't
> it?
Right. There's always a degree of _glossing_ when we condense into one
sentence what would take a few paragraphs to detail in full. What I
intended to say there, however, could be symbolized as TRUE(P);
FALSE(P) or, using ordered pair notation, (P,TRUE); (P,FALSE).
(Please see more below).
>
> Do you mean
>
> It is possible to know P.
>
> means
>
> P has a truth value (true or false) and that truth value is to be
> (or has been?) found by reasoning in the meta theory.
>
> ?
We're virtually in agreement here. However, I'd like to stress that
clarity of terminologies (in details) have to be absolutely clear
so as we could know for certain whether or not we'd finally have
agreement.
So, first of all, let's reserve the lower case 'true', 'false'
for FOL model-theoretical truth and falsehood, while the Upper
case 'TRUE', 'FALSE', for meta level reasoning truth and falsehood.
For examples:
- true(0 < S0) is a model-theoretical truth.
- false(S0 < 0) is a model-theoretical falsehood.
While:
- TRUE(true(0 < S0)) is a meta level reasoning truth.
- TRUE(false(S0 < 0)) is a meta level reasoning truth.
- FALSE(false(0 < S0)) is a meta level reasoning falsehood.
- TRUE(FALSE(false(0 < S0))) is a meta level reasoning truth.
- TRUE(If T is a first order formal system => T |- (x=x))
is a meta level reasoning truth.
- FALSE(NEG(PA |- (x=x)) is a meta level reasoning falsehood.
- TRUE(FALSE(NEG(PA |- (x=x))) is a meta level reasoning truth.
where NEG(P) <=> The negation of P (as a meta statement).
Convention: where the context is clear, TRUE and true are
interchangeable and so are FALSE and false.
But _only when the context is clear_ .
In brief, TRUE(P) isn't just the binary value TRUE (ditto for
FALSE(P)): it's an ordered pair (P, TRUE) as mentioned above.
Secondly, in your "found by reasoning in the meta theory", we can
discard "meta theory" since all that's required here is just
meta inference, meta reasoning, based on:
- Boolean algebra of TRUE and FALSE values of the meta predicates
(P0, P1, P2, ....). For example:
TRUE(P) and TRUE(P') => TRUE(P and P')
- MP rule of inference on meta predicates. For instance:
TRUE(If T is a first order formal system => T |- (x=x)) [Meta "axiom"]
TRUE(PA is a formal system) [Meta knowledge/stipulation/theorem]
---------------------------
TRUE(PA |- (x=x)) [Meta conclusion].
- etc..
The "etc..." signifies we're not going to list all the meta inference
rules, or all the meta "axioms" or foundational assumed knowledge about
FOL reasoning. It's sufficient to note that (a) in this and related
threads only the familiar ones would be needed, and (b) at any rate,
the collection of these meta rules and "axioms" is _finite_ so there's
no danger that we wouldn't know/agree what they be.
Now then, TRUE(P), is actually an conclusion (I used "outcome" as
an alias) of a meta inference. In a bit more detail TRUE(P) is
actually the triplet:
TRUE(P) df= (TRUE, meta-proof-or-inference-of-P, P).
Hence my "the collection of valid meta inference outcomes"
is K:
K = {(TRUE, meta-proof-or-inference-of-P, P)'s}.
So Def1a is really:
Def1a. "It's possible to know, to assert the (meta level) truth value
of P" <=>
"There is in K a triplet:
(TRUE, meta-proof-or-inference-of-P, P)
or
There is in K a triplet:
(TRUE, meta-proof-or-inference-of-NEG(P), NEG(P))
"
>
>> Def1b. "It's impossible possible to know, to assert the (meta level)
>> truth value of P" <=> "It's _NOT_ possible to know, to assert
>> the (meta level) truth value of P".
>>
>> Where "possible" is in the sense of Def1a.
So, per the above, my Def1b. stills stand as is.
>
> If so, then
>
> It is impossible to know P.
>
> means
>
> Either P has no truth value, or, if it has a truth value
> that truth value will not be (or hasn't yet been?) found
> by reasoning in the meta theory.
No. Logical reasoning is _time agnostic_ (as well as non-psychological)
hence "will not be" and "hasn't yet been" can't be used to qualify
a technical definition.
As just mentioned, my Def1b. stills stand as is.
>
> Maybe.
>
Agree that it may be. But in the final analysis, No.