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Science Forum Index » Logic Forum » Liar's Paradox
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| Daryl McCullough |
Posted: Thu Apr 03, 2008 11:38 am |
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Marshall says...
Quote: On Apr 3, 5:58 am, stevendaryl3...@yahoo.com (Daryl McCullough) wrote:
But then what about
the sentence
This sentence cannot be assigned a truth value, since it
involves infinite regress.
Meh. It requires orders of magnitude more machinery to
formalize than the previous ones, and what would be the
lesson learned in doing so? That trying to model natural
language formally is a bad idea?
It doesn't have anything to do with natural language,
specifically. It has to do with the meaning of the
predicate "true".
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Daryl McCullough
Ithaca, NY |
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| Daryl McCullough |
Posted: Thu Apr 03, 2008 12:29 pm |
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Marshall says...
Quote: On Apr 3, 8:38 am, stevendaryl3...@yahoo.com (Daryl McCullough) wrote:
It doesn't have anything to do with natural language,
specifically. It has to do with the meaning of the
predicate "true".
I have no idea what you're driving at.
That the Liar Paradox has nothing to do with natural language,
specifically.
Quote: My default conception of "true" is that it is one of
two values in the boolean domain,
Well, a *sentence* is neither equal to the boolean
value true nor is it equal to the boolean value false.
So how does it make any sense to call a statement
true or false?
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Daryl McCullough
Ithaca, NY |
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| Daryl McCullough |
Posted: Thu Apr 03, 2008 12:37 pm |
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Marshall says...
Quote: My default conception of "true" is that it is one of
two values in the boolean domain, and my default
conception of evaluating expressions is within a
computational model.
Given any computational model M for evaluating sentences,
one can come up with a sentence G_M such that
G_M <-> M does not succeed in reducing G_M to "true"
That would seem to mean that you *can't* identify truth
with any particular computational model.
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Daryl McCullough
Ithaca, NY |
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| Daryl McCullough |
Posted: Thu Apr 03, 2008 12:41 pm |
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Marshall says...
Quote:
On Apr 3, 8:12 am, "Jesse F. Hughes" <je...@phiwumbda.org> wrote:
As usual, "This statement is not true" yields a paradox even with
Marshall's third possibility.
I suppose I see what you mean, but I have to point out that
under a wide range of evaluation models, "not true" and
"false" are exactly the same thing, so your above sentence
would be the same as the liar's paradox.
No, "false" and "not true" are not the same thing. A false
statement is one whose *negation* is true.
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Daryl McCullough
Ithaca, NY |
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| Daryl McCullough |
Posted: Thu Apr 03, 2008 12:43 pm |
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Marshall says...
Quote: I may just be overly pragmatic in my thinking, but I really
don't see the value to the logician of riddles.
Natural language has ambiguous, nondeterministic,
context-sensitive semantics by design and intent.
The Liar Paradox doesn't have anything specifically to do with
natural language.
--
Daryl McCullough
Ithaca, NY |
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| LauLuna |
Posted: Thu Apr 03, 2008 1:48 pm |
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On Apr 3, 3:58 pm, stevendaryl3...@yahoo.com (Daryl McCullough) wrote:
Quote: Marshall says...
I take the view that the paradoxical aspect isn't the real issue
with the Liar's Paradox; rather it's the infinite regress, which
is every bit as present in the Truth Teller as in Liar. Neither
statement can be assigned a truth-value because both
statements require that they be assigned a truth value
before they can be assigned a truth value.
Then we have three types of sentences, true, false, and
sentences involving infinite regress. But then what about
the sentence
This sentence cannot be assigned a truth value, since it
involves infinite regress.
But then what about
the sentence
This sentence cannot be assigned a truth value, since it
involves infinite regress.
Call it 'S'. If S says anything at all, it expresses the conjunction
of:
1. S cannot be assigned a truth value.
2. Trying to assign S a truth value involves infinite regress.
3. The cause of the said in 1. is the said in 2.
Or perhaps simply 2. would suffice.
It could be (provably) false without contradiction and it could be
unprovably true.
But if we are engaged in a process of comparing what S says with
reality in order to determine its truth value, we must ask at some
step of the process whether the process involves infinite regress.
This takes us back to the first step of the process.
So, we are in fact involved in an infinite regress when try to
ascertain S's truth value.
Then, according to the clause that such sentences lack any truth
value, S lacks any truth value. Note that lacking any truth value can
be no truth value.
This does not necessarily render S true since S can be unable to make
the unique statement it would be making in English if it could make
any. I think this could only happen if S fails in referring the way it
is required in order to possess a truth value.
As usual, this leads to a sort meta-paradox (the way the Strengthened
Liar does):
S1) Trying to assign a truth value to S1 involves infinite regress.
We are compelled to pronounce S1 untrue and still assert:
'Trying to assign a truth value to S1 involves infinite regress'
Tokenism is called for now. Some tokens of S1 express a proposition
and some others don't.
And now:
S2) Trying to assign a truth value to any token of S2 involves
infinite regress.
If all tokens of S2 are able to effectively refer to all tokens of S2,
then no token of S2 can be true and if some were false, there would
also be a true one. Then we could plausibly be at the same time
compelled to assert some token of S2.
So, plausibly not all tokens of S2 succeed in referring to all tokens
of S2.
But if you rather meant something like:
S3) Trying to ascertain whether S3 is true, false or involves
infinite regress, involves infinite regress
This is again the same story all along.
Regards |
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| LauLuna |
Posted: Thu Apr 03, 2008 2:00 pm |
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On Apr 3, 4:58 am, raydpratt <raydpr...@gmail.com> wrote:
Quote: When we call a statement true or false, we are saying that we have
compared that statement to a given fact or principle and either found
corraboration or contradiction. For example, if we say "All apples
are cubes that glow in the dark," we can only judge that statement as
being true or false by comparing the statement to what we know about
apples.
In the Liar's Paradox, we say "This very statement is false." The
alleged paradox is that if the statement is true, then it is false as
it claims, but if it is false as it claims, then it has stated the
truth and cannot be false, ad infinitum. Properly understood,
however, there is no paradox.
To judge the truth or falsity of "This very statement is false," we
must compare the statement not only to itself as explicitly required,
but also to what we know about finding the falsity of any general
statement. This is implied by the use of the term "false," much like
the term "apple" would require us to compare a statement to what we
know about apples. With the Liar's Paradox, the very fact of the
supposed paradox proves that the statement cannot be definitively
proven false. And as such, the statement is ultimately true because
it admits that it falsely asserts that it is provably false.
Similarly, in the Truth Teller, we say "This very statement is true."
Although there is no alleged paradox, the statement's self-reference
to its own veracity is not sufficient evidence for its truth. The
informal fallacy called petitio principii, or begging the question,
occurs where a questioned fact is called in as proof of that fact, and
such proofs are always illegitimate. However, we can go further here
and say that the statement is definately false because it falsely
claimed that it was provably true.
Very Respectfully,
Ray Donald Pratt
I find two doubtful points in your approach.
1. 'This very statement is true' does not claim it is PROVABLY true.
2. You wrote:
Quote: With the Liar's Paradox, the very fact of the
supposed paradox proves that the statement cannot be definitively
proven false. And as such, the statement is ultimately true because
it admits that it falsely asserts that it is provably false.
How can a statement be ultimately true on the grounds that it admits
that it FALSELY claims something? If it is true, then what it admits
is true, and then it falsely claims whatever it claims; thus it is
false.
3. What does the 'ultimately' in 'is ultimately true' mean? This
should be clarified.
I agree on your general approach but not on the conclusions you draw.
Regards |
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| Daryl McCullough |
Posted: Thu Apr 03, 2008 2:06 pm |
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Marshall says...
Quote:
On Apr 3, 9:29 am, stevendaryl3...@yahoo.com (Daryl McCullough) wrote:
Marshall says...
On Apr 3, 8:38 am, stevendaryl3...@yahoo.com (Daryl McCullough) wrote:
It doesn't have anything to do with natural language,
specifically. It has to do with the meaning of the
predicate "true".
I have no idea what you're driving at.
That the Liar Paradox has nothing to do with natural language,
specifically.
Okay, perhaps I wasn't explicit enough with my original reply.
My reaction to your statement, "The Liar Paradox has nothing to
do with natural language" is yes, the same issue shows up in
other contexts besides natural language ones, which can be
seen by translating Liar's from its natural language form into a
formal language. However I don't understand *why* you're saying
this particular sentence at this point.
Because you said
Quote: Meh. It requires orders of magnitude more machinery to
formalize than the previous ones, and what would be the
lesson learned in doing so? That trying to model natural
language formally is a bad idea?
That *seems* to be implying that there is a connection
between understanding the Liar Paradox and modeling
natural language formally.
Quote: Well, a *sentence* is neither equal to the boolean
value true nor is it equal to the boolean value false.
So how does it make any sense to call a statement
true or false?
Um, I'm guessing you're asking leading questions as
part of some sort of pedagogical technique.
Look, you made a post about the Liar Paradox. I don't
think that your post made very much sense. But if you're
not interested in defending it, I'll let it drop.
--
Daryl McCullough
Ithaca, NY |
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| Daryl McCullough |
Posted: Thu Apr 03, 2008 2:16 pm |
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In article <ccf1f7a9-3cd1-4212-9a36-b2793ffb6613@s8g2000prg.googlegroups.com>,
Marshall says...
Quote:
On Apr 3, 9:43 am, stevendaryl3...@yahoo.com (Daryl McCullough) wrote:
Marshall says...
I may just be overly pragmatic in my thinking, but I really
don't see the value to the logician of riddles.
Natural language has ambiguous, nondeterministic,
context-sensitive semantics by design and intent.
The Liar Paradox doesn't have anything specifically to do with
natural language.
Do you see your reply as having some relevance to what
I wrote?
Yes. You said: "Natural language has ambiguous, nondeterministic,
context-sensitive semantics by design and intent". I responded
by saying that that has nothing to do with the Liar Paradox
(the subject of this thread). Maybe you didn't intend for your
statement to have any relevance to this thread?
--
Daryl McCullough
Ithaca, NY |
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| Daryl McCullough |
Posted: Thu Apr 03, 2008 3:11 pm |
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Marshall says...
Quote:
On Apr 3, 11:16 am, stevendaryl3...@yahoo.com (Daryl McCullough)
wrote:
Do you see your reply as having some relevance to what
I wrote?
Yes. You said: "Natural language has ambiguous, nondeterministic,
context-sensitive semantics by design and intent". I responded
by saying that that has nothing to do with the Liar Paradox
(the subject of this thread). Maybe you didn't intend for your
statement to have any relevance to this thread?
Have you found success in the past with the technique of
repeating the same phrase over and over again in response
to requests for clarification?
Okay, I have no idea what your point is. You have no idea
what my point is. Let's drop it.
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Daryl McCullough
Ithaca, NY |
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| Daryl McCullough |
Posted: Thu Apr 03, 2008 3:13 pm |
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Marshall says...
Quote:
On Apr 3, 11:06 am, stevendaryl3...@yahoo.com (Daryl McCullough)
wrote:
Marshall says...
Um, I'm guessing you're asking leading questions as
part of some sort of pedagogical technique.
Look, you made a post about the Liar Paradox. I don't
think that your post made very much sense. But if you're
not interested in defending it, I'll let it drop.
If you think something I wrote didn't make much sense,
I'd invite you to point out what you object to specifically.
I don't think that would be very fruitful. Let's drop it.
--
Daryl McCullough
Ithaca, NY |
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| Newberry |
Posted: Thu Apr 03, 2008 6:51 pm |
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On Apr 2, 7:58 pm, raydpratt <raydpr...@gmail.com> wrote:
Quote: When we call a statement true or false, we are saying that we have
compared that statement to a given fact or principle and either found
corraboration or contradiction. For example, if we say "All apples
are cubes that glow in the dark," we can only judge that statement as
being true or false by comparing the statement to what we know about
apples.
In the Liar's Paradox, we say "This very statement is false." The
alleged paradox is that if the statement is true, then it is false as
it claims, but if it is false as it claims, then it has stated the
truth and cannot be false, ad infinitum. Properly understood,
however, there is no paradox.
To judge the truth or falsity of "This very statement is false," we
must compare the statement not only to itself as explicitly required,
but also to what we know about finding the falsity of any general
statement. This is implied by the use of the term "false," much like
the term "apple" would require us to compare a statement to what we
know about apples. With the Liar's Paradox, the very fact of the
supposed paradox proves that the statement cannot be definitively
proven false. And as such, the statement is ultimately true because
it admits that it falsely asserts that it is provably false.
No. Just like you compared "All apples are cubes that glow in the
dark" to reality, you have to compare "this sentence is false" to
reality. But it CANNOT be compared to reality, hence it is
meaningless. Since it cannot be compared to reality it is not a
picture of any possible state of affairs. It is as simple as that!
Quote:
Similarly, in the Truth Teller, we say "This very statement is true."
Although there is no alleged paradox, the statement's self-reference
to its own veracity is not sufficient evidence for its truth. The
informal fallacy called petitio principii, or begging the question,
occurs where a questioned fact is called in as proof of that fact, and
such proofs are always illegitimate. However, we can go further here
and say that the statement is definately false because it falsely
claimed that it was provably true.
Very Respectfully,
Ray Donald Pratt |
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| Jesse F. Hughes |
Posted: Fri Apr 04, 2008 6:09 am |
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Newberry <newberryxy@gmail.com> writes:
Quote: No. Just like you compared "All apples are cubes that glow in the
dark" to reality, you have to compare "this sentence is false" to
reality. But it CANNOT be compared to reality, hence it is
meaningless. Since it cannot be compared to reality it is not a
picture of any possible state of affairs. It is as simple as that!
How is it that I can't compare "This sentence is false" to reality,
but I *can* compare "This sentence has five words" to reality?
--
Jesse F. Hughes
"Leaving things always seems to fix me,
Running seems to ease my worried mind."
-- Bad Livers, "Honey, I've Found a Brand New Way" |
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| Newberry |
Posted: Fri Apr 04, 2008 4:30 pm |
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On Apr 4, 4:09 am, "Jesse F. Hughes" <je...@phiwumbda.org> wrote:
Quote: Newberry <newberr...@gmail.com> writes:
No. Just like you compared "All apples are cubes that glow in the
dark" to reality, you have to compare "this sentence is false" to
reality. But it CANNOT be compared to reality, hence it is
meaningless. Since it cannot be compared to reality it is not a
picture of any possible state of affairs. It is as simple as that!
How is it that I can't compare "This sentence is false" to reality,
but I *can* compare "This sentence has five words" to reality?
Did you try it? You can very easily compare the later to reality by
counting the number of words in it. You cannot compare the former to
reality because in order to that you have to compare it reality etc.
The semantic of "this sentence is false" is such that you get into an
infinite regress. |
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| Marshall |
Posted: Fri Apr 04, 2008 4:53 pm |
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On Apr 4, 3:09 am, "Jesse F. Hughes" <je...@phiwumbda.org> wrote:
Quote: Newberry <newberr...@gmail.com> writes:
No. Just like you compared "All apples are cubes that glow in the
dark" to reality, you have to compare "this sentence is false" to
reality. But it CANNOT be compared to reality, hence it is
meaningless. Since it cannot be compared to reality it is not a
picture of any possible state of affairs. It is as simple as that!
How is it that I can't compare "This sentence is false" to reality,
but I *can* compare "This sentence has five words" to reality?
Would you agree that the mapping from sentences to the
number of words in the sentence is total?
Would you suppose the mapping from sentences to the truth
value of the sentence would be partial or total?
Marshall |
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